Table of contents

''NanoSPD'' means Nano–material by Severe Plastic Deformation (SPD), which is an efficient way to obtain bulk nano–structured materials. During SPD, the microstructure of the material is transformed into a very fine structure consisting of ultra fine grains (UFG) approaching even the nano–scale. SPD is different from classical large strain forming processes in two aspects: 1. The sample undergoes extremely large strains without significant change in its dimensions, 2. In most SPD processes high hydrostatic stress is applied which makes it possible to deform difficult–to–form materials.

This conference is part of a series of conferences taking place every third year; the history of NanoSPD conferences began in 1999 in Moscow (Russia), followed by Vienna in 2002 (Austria), Fukuoka in 2005 (Japan), Goslar in 2008 (Germany), Nanjing in 2011 (China), and Metz in 2014 (France).

The preface continues in the pdf.

Abstract. The Université de Lorraine in Metz, France, is the selected site for the 6th International Conference on Nanomaterials by Severe Plastic Deformation (NanoSPD6) following a series of five earlier conferences. This introductory paper reports on several major developments in NanoSPD activities as well as on very recent NanoSPD citation data which confirm the continued growth and expansion of this important research area. Close attention is given to the topics of workshops, conferences and seminars organized during these last three years as well as on books and reviews published prior to the NanoSPD6 conference. A special concern of the committee is in introducing and discussing the appropriate terminology to be applied in this new field of materials science and engineering.

All papers published in this volume of IOP Conference Series: Materials Science and Engineering have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The accumulative press bonding (APB) process used as a novel technique in this study provides an effective alternative method for manufacturing Al/10 vol.% WC_p metal matrix composites (MMCs). The results revealed that by increasing the number of APB cycles (a) the uniformity of WC particles in aluminum matrix improved, (b) the porosity of the composite eliminated, (c) the particle free zones decreased. The X-ray diffraction results also showed that nanostructured Al/WC_p composite with the average crystallite size of 58.4 nm was successfully achieved by employing 14 cycles of APB technique. The tensile strength of the composites enhanced by increasing the number of APB cycles, and reached to a maximum value of 216 MPa at the end of 14th cycle, which is 2.45 and 1.2 times higher than obtained values for annealed (raw material, 88 MPa) and 14 cycles APB-ed monolithic aluminum (180 MPa), respectively

In the present work, a novel technique is introduced called CAPB (continual annealing and press bonding) for the manufacturing of a bulk aluminum matrix composite dispersed with 10 vol.% WC particles (Al/WC_p). The microstructure of the fabricated composite after fourteen cycles of CAPB showed an excellent and homogenous distribution of the WC particles in the aluminum matrix and strong bonding between the various layers. The results indicated that the tensile strength of the composites increased with the number of CAPB cycles, and reached a maximum value of 140 MPa at the end of fourteenth cycle, which was 1.6 time higher than the obtained value for annealed aluminum (raw material, 88 MPa). Even though the elongation of the Al/WC_p composite was reduced during the initial cycles of CAPB-ing, it increased significantly during the final cycles.

The innovative forming processes Linear Flow Splitting (LFS) and Linear Bend Splitting (LBS) were developed to facilitate the continuous production of branched profiles with tailored sheet thickness by inducing severe plastic strain. In contrast to most SPD processes the stress state in LFS and LBS is very complex and plastic deformation is confined to limited volumes which results in steep strain gradients and consequently ultrafine grained (UFG) gradient microstructures. Even though the processes have been commercialized, the increased lightweight potential that originates from the local grain refinement remains mostly idle since it is neither fully understood nor easily assessable yet.

The present work shows the state of the art for the LFS and LBS processes and compares the microstructures and distribution of mechanical properties for different steels processed with different LFS parameters. The data is used to identify characteristic manufacturing induced properties that are insensitive to processing parameters. Based on the experimental results a material flow model for the processing zone is proposed which is discussed with respect to the current understanding of plasticity at severe strains.

Conventional equal channel angular pressing is an efficient technique to obtain bulk ultrafine grained materials (UFG) with extraordinary mechanical properties in the form of rods. In this work, an incremental method of ECAP process which allows to obtain thick sheets with UFG structure is presented. Using this method square plates (62 × 62 mm) were obtained. In this case, a combined route – A+ specific B – with 90 degree rotation along plate normal after each pass keeping other planes in the same positions relatively to the channel – has been applied. The efficiency of this methods was proved for technically pure 1050 aluminium. It was processed by incremental ECAP using 8 passes of A+B route. To characterize microstructure visible light microscopy and transmission electron microscopy were used. Mechanical properties were measured by microhardness test. The results obtained showed that the microstructure and mechanical properties of 1050 aluminium alloy processed by incremental ECAP are comparable to conventional ECAP. However, the new processing method broaden the potential applications of UFG materials.

We have proposed a new extrusion process combined with torsion. Extrusion-torsion simultaneous processing is a very attractive technique for fabricating a rod-shape material with high strength and excellent workability. The grain size of AZ91D magnesium alloy was gradually decreased with increasing the torsion speed in as extrusion-twisted conditions. Grain refinement under 2um was achieved by the optimized extrusion-torsion condition. Hardness was increased by the addition of torsion speed comparing with as solution-treated and as extruded samples. Hardness change was dependent on the extrusion-torsion temperature.

The paper proposes a new variation of the application of SPD methods. For the suggested TCMAP (twist channel multi angular pressing) technology a larger strain is imposed more effectively while homogeneity of material is increased. The number of passes needed to obtain the ultra-fine to nano-scale grains in bulk materials can be significantly reduced. Commercially pure Al (99.97%) was used for the experimental verification of the suggested process. The deformation parameters of the process were also described using a numerical simulation based on a FE analysis. The predicted value of imposed strain after a single pass reached approximately 2.7. Deformation homogeneity was confirmed by micro-hardness tests. Due to the designed shape of the channel both ends of the processed sample are defined by a higher imposed strain and vertical faces.

Nanostructured materials are known to exhibit attractive properties, especially in the mechanical field where high hardness is of great interest. The friction stir process (FSP) is a recent surface engineering technique derived from the friction stir welding method (FSW). In this study, the FSP of an 316L austenitic stainless steel has been evaluated. The treated layers have been characterized in terms of hardness and microstructure and these results have been related to the FSP operational parameters. The process has been analysed using a Response Surface Method (RSM) to enable the stirred layer thickness prediction.

The techniques of severe deformation of steel samples have been investigated – drawing and shear drawing in eccentric dies implemented at room temperature. The paper considers the features of structural changes occurring in low-carbon steel at different types of deformation treatment – conventional drawing and shear drawing of samples made of steel 10. The structural parameters and the nature of distribution of the plastic deformation intensity were investigated. Higher efficiency of the drawing process with shear was revealed in terms of strain intensity accumulation. A comparative analysis of structural changes and microhardness distribution over the bulk of samples produced by the investigated methods was conducted. The repeatability of the stress-strain state parameters obtained through physical and mathematical modeling was shown. The analysis of the obtained results leads to the conclusion that the use of drawing with shear is advanced for the production of samples and billets with high strength and sufficiently high ductility by creating a gradient structure.

The most considerable factors influencing flow uniformity and a strained state of billets, respectively, structure formation processes and ECAP techniques with industrial potential have been studied. It is shown that the industrial potential of ECAP techniques largely depends on the intensity of strain accumulation per a processing cycle. Enhancement of this value considerably reduces the labor intensity of manufacturing of semi-products with an ultrafinegrained (UFG) structure.

Incremental ECAP (I-ECAP) can be used for SPD of continuous bars, plates and sheets. This paper describes design, construction and preliminary trials of a prototype machine capable of processing thick continuous plates. To increase productivity, a two-turn I-ECAP is used, which is equivalent to route C in conventional one-turn ECAP. The machine has a reciprocating punch inclined at 45°, a clamp holding the plate in the die during deformation and a feeder incrementally feeding the plate when it is not deformed; all these devices are driven by hydraulic actuators controlled by a PLC. The machine is capable of deforming materials at room temperature as well as elevated temperatures. The die is heated with electric heaters. The machine has also an integrated cooling system and a lubrication system. The material used for the initial trials was Al 1050 plate (10×50×1000) conversion coated with calcium aluminate and lubricated with dry soap. The process was carried out at room temperature using 1.6 mm feeding stroke and a low cycle frequency of approximately 0.2 Hz. The UFG structure after the first pass of the process revealed by STEM confirms process feasibility.

A major problem in Equal Channel Angular Pressing is die design. Friction plays an important role in the extrusion process. In the present work, Aluminium 6082 alloy was processed through a modified ECAP die originally proposed by Mathieu et al. in 2004 [1] and the performance of the die was analyzed. The channel angle was ϕ=90° and corner angle ψ=20°. Mechanical properties, micro hardness measurement and crystalline size (D) were measured from the extruded specimen for both the conventional and new die designs. It has been found that the new die samples displayed better results than the conventional ones. The newly designed die reduced the effect of friction on the work piece, it increased the tensile strength, the hardness of the material and achieved better grain refinement.

The principal KoBo device is a press with a forward-backward rotating die, enabling the extrusion of ingots under conditions of constant destabilization of their substructure. Polycrystalline grade 2 titanium was subjected to warm KoBo type extrusion. Microstructure of the material was investigated by means of Electron Backscatter Diffraction (EBSD) in the scanning electron microscope. It clearly shows deformation-induced grain fragmentation. The EBSD maps reveal heterogeneous microstructure built of ribbons curled about the extrusion direction (ED) and some equiaxed or cigar-like grains. Sizes of grains vary in the range 70 – 1500 nm for the minor axis and 350 – 20000 nm for the major axis. The material has a relatively sharp nearly axial texture with the <0001> axis perpendicular to ED. In misorientation angle distribution, besides the peak at low angle boundaries, there are three other peaks at about: 29.7deg, 89.7deg and 93.2deg. They do not correspond to any twin boundaries or low Σ coincidence site lattice misorientations.

In order to produce ultrafine grained structures, interstitial-free steel sheets have been processed using a novel severe plastic deformation technique semi continuous equal channel angular extrusion (SC-ECAE) which is based on equal channel angular extrusion (ECAE) in an incremental way. The deformation was carried out at room temperature and individual specimen was repeatedly processed to various passes. An overall grain size which is 0.55 μm was achieved after 10 passes (or an equivalent total strain of 4.8). The present paper reports the evolution of microstructures during deformation, which were examined and characterized using high resolution EBSD in a field emission gun SEM. The mechanisms of grain refinement are discussed.

In this paper, the effects of Surface Mechanical Attrition Treatment on the high- temperature oxidation of AISI 316L austenitic stainless steel are investigated. Samples treated with different conditions were oxidized at 750°C in order to study the effect of this type of nanocrystallisation on the oxidation resistance of the alloy concerned. X-ray diffraction and in- situ Raman spectroscopy were used to identify the oxides formed at the surface. The results indicate the presence of hematite, magnetite and chromium oxides. Experimental results obtained by Raman spectroscopy were also used to study the stress evolution in Cr₂O₃ films during isothermal conditions.

75%Al-25%Nb powder composites, fabricated by square shape cold extrusion, were subject to shot peening treatment with full coverage. Shot peening results in a high number of intense local deformations, with a surface roughness in our case of about l6gm. Due to the high local deformation down to nano-scale surface grain refinement and strain accumulation was generated. Previous texture characterization was performed by neutron diffraction and laboratory X-rays (Cu K_α radiation). The first method took advantage of the high penetration power and averaging capabilities and the second method was further used taking advantage of the low penetration to characterize surface microstructure modification. Peak broadening, before and after shot peening, was analyzed by MAUD software and domain sizes and microstrains were calculated for both phases. Simultaneous EBSD and EDS scans, on 30 nm step sizes, were performed on a FESEM Quanta 200 + TSL-EDAX, showing the highly heterogeneous microstructure developed because of shot peening. Protrusions, due to particle impacts, are clearly seen on EBSD maps. Results mainly revealed that, for Al phase, domain sizes decrease, while microstrains and dislocation densities consistently increase after the materials have been subjected to SP. For Nb phase the visible effect of SP is an increment of microstrains, and related dislocation densities, but keeping the domain sizes almost constant.

An in situ study of flow in severe plastic deformation (SPD) of surfaces by sliding is described. The model system – a hard wedge sliding against a metal surface – is representative of surface conditioning processes typical of manufacturing, and sliding wear. By combining high speed imaging and image analysis, important characteristics of unconstrained plastic flow inherent to this system are highlighted. These characteristics include development of large plastic strains on the surface and in the subsurface by laminar type flow, unusual fluid-like flow with vortex formation and surface folding, and defect and particle generation. Preferred conditions, as well as undesirable regimes, for surface SPD are demarcated. Implications for surface conditioning in manufacturing, modeling of surface deformation and wear are discussed.

Aluminium alloy 2014 is an important age hardening alloy for aerospace industries. Effect of ultrasonic shot peening (USSP) in peak aged condition of this alloy was studied on its surface microstructure, tensile properties and low cycle fatigue behavior. The structure of the USSP treated specimens, close to surface was characterized by X-ray diffraction and transmission electron microscopy. The top surface region was found to contain nanosize grains of ~30 nm. Both yield as well as tensile strength was found to increase progressively with increasing duration of shot peening for 10, 15 and 20 minutes. LCF behavior was studied following ultrasonic shot peening for 10 minutes, at three total strain amplitudes (Δε_t/2) of ±0.4%, ±0.5% and ±0.6%.

When ductile alloys are subject to sliding wear, small increments of plastic strain accumulate into severe plastic deformation and mechanical alloying of the surface layer. The authors constructed a simple coaxial tribometer, which was used to study this phenomenon in wrought Al-Sn and cast Cu-Mg-Sn alloys. The first class of materials is ductile and consists of two immiscible phases. Tribological modification is observed in the form of a transition zone from virgin material to severely deformed grains. At the surface, mechanical mixing of both phases competes with diffusional unmixing. Vortex flow patterns are typically observed. The experimental Cu-Mg-Sn alloys are ductile for Mg-contents up to 2 wt% and consist of a- dendrites with a eutectic consisting of a brittle Cu₂Mg-matrix with α-particles. In these, the observations are similar to the Al-Sn Alloys. Alloys with 5 wt% Mg are brittle due to the contiguity of the eutectic compound. Nonetheless, under sliding contact, this compound behaves in a ductile manner, showing mechanical mixing of a and Cu₂Mg in the top layers and a remarkable transition from a eutectic to cellular microstructure just below, due to severe shear deformation. AFM-observations allow identifying the mechanically homogenized surface layers as a nanocrystalline material with a cell structure associated to the sliding direction.

Under repeated impact loadings that are encountered during peening process, surface mechanical attrition treatment or erosive wear, metals undergo severe plastic deformation which may lead to a local refinement of their microstructure in the near-surface. These mechanically-induced surface nano-structures exhibit very interesting physical properties such as high hardness and better tribological properties, ... Strong research efforts have been undertaken during the last years to understand the mechanism explaining how these nanostructures are created and grow under such loadings. It is commonly accepted that the shear stress induced by oblique impacts is the driving force for such mechanical transformations. Nevertheless, we have recently observed that normal impacts may also lead to such grain refinement. In this paper, this mechanism is investigated on a AISI1045 steel submitted to different heat treatments. A phenomenological mechanism based on a previous work is presented and shows a good efficiency on the air cooled sample. Nevertheless it failed to explain the differences observed between the different samples, showing the necessity to take into account both the material stress-strain curve and the microstructural state.

The Surface Mechanical Attrition Treatment is a recent technique leading to the formation of nanostructured layers by the repeated action of impacting balls. While several communications have revealed possible contamination of the SMATed surfaces, the nature of this surface contamination was analyzed in the present contribution for the treatment of an AISI 316L stainless steel. It is shown, by a combination of Transmission Electron Microscopy and Glow Discharge – Optical Emission Spectrometry, that the surface was alloyed with Ti, Al and V coming from the sonotrode that is used to move the balls as well as Zr coming from the zirshot® balls themselves.

This work deals with the influence of surface mechanical attrition treatment (SMAT) on fatigue properties of a medical grade 316L stainless steel. Metallurgical parameters governed by SMAT such as micro-hardness and nanocrystalline layer are characterized using different techniques. Low cycle fatigue tests are performed to investigate the fatigue properties of untreated and SMAT-processed samples. The results show that the stress amplitude of SMAT- processed samples with two different treatment intensities is significantly enhanced compared to untreated samples, while the fatigue strength represented by the number of cycles to failure is not improved in the investigated strain range. The enhancement in the stress amplitude of treated samples can be attributed to the influence of the SMAT affected layer.

A bimodal grain structure comprising of ultrafine-grained (UFG) and coarse-grained (CG) regions was produced in Al6063 by means of powder metallurgy route. Nanocrystalline Al alloy powder was synthesized by high energy mechanical milling using a planetary ball mill under Ar atmosphere for 22.5 h. The as-milled powder was mixed with 30 vol.% unmilled powder and consolidated by extrusion at 450 °C with an extrusion ratio of 9:1. UFG and CG billets were also fabricated at the same condition by using milled and unmilled AI6063 powders, respectively. The grain structure was studied by scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) techniques. The deformation behavior under uniaxial tension was investigated. The bimodal Al6o63 showed balanced mechanical properties, including enhanced yield and ultimate strength comparable UFG alloy with reasonable ductility analogous CG material. The fracture surfaces demonstrated a ductile fracture mode, in which the dimple size was related to the grain structure. The ductility enhancement mechanisms in nanostructured Al6o63 with bimodal grain structure were discussed.

The application of High-Pressure Torsion (HPT) to two different Co-Cu alloys permits the generation of materials with nanocrystalline grain sizes. The evolution of the microstructure with increasing strain and the resulting microstructure are investigated by scanning electron microscopy. The final attainable grain sizes are significantly smaller than in corresponding pure metals deformed by HPT. Special attention is given on microstructural evolution and deformation behavior of the Cu and Co phases revealing the importance of nature, morphology and deformation behavior of the single phases on the formation of nanocrystalline structures during HPT processing.

In this paper iron powders with two oxygen content (0.2 and 0.6% wt.) have been mechanically milled and consolidated by hot static pressing at different temperatures to obtain different grain sizes. At lower temperatures the grain size was in the nanostructured and ultrafine range and with increasing temperature abnormal grain growth was observed for both compositions. This led to the development of bimodal grain size distributions. In the samples with lower oxygen content the grain size and the percentage of coarse grain areas were larger than in the case of high oxygen content.

The strength and ductility have been determined by tensile tests. For low oxygen content, the presence of large coarse grains allowed plastic strain in some cases, and for the samples consolidated at higher temperatures, yield strength of 865 MPa with a 8% total strain were obtained. For the samples with high oxygen content plastic deformation was no possible in any case.

The observed stress for both compositions was analysed by two approaches, one based exclusively in grain boundary strengthening and the other one based in two effects acting at the same time: grain boundary and particle strengthening. Whereas grain boundary strengthening seems to fit with the strength of the samples in the nanostructured range, when coarse ferrite grains appear the addition of particle strengthening help to get better results. This indicates that the presence of oxides dissolved inside the large grains reinforce the structure of ball-milled iron.

Mechanical Attrition of metallic powders induces severe plastic deformation and consequently reduces the average grain size. Powders of 99.7 Al (45μm particle size), cryomilled for 7 hrs having a crystal size of ~ 20 nm, were consolidated by high frequency induction sintering under a constant pressure of 50 MPa and at two temperatures of 500 and 550 °C for two sintering dwell times of 1 and 3 minutes at a constant heating rate of 400 °C/min. The bright field TEM image and X-ray line broadening technique, for the cryomilled powders, were used to measure-the crystallite size. Simple compression at an initial strain rate of 10⁻⁴ s⁻¹ was conducted at room temperature, 373 and 473 K, and the yield strength was documented and correlated with the sintering parameters. The as-received 99.7 Al powders-consolidated using one of the sintering parameters was used as a reference material to compare the mechanical properties. Hardness, density and crystal size of the consolidated sample, that gave the highest yield and fracture strength, were measured.

Deformation behavior of two phase materials with High-Pressure Torsion (HPT) was investigated on the basis of Cu-composites. As second phases Fe, W and yttria were used. The deformation behavior in the HPT-process differs due to their different mechanical properties and the ratio of Cu and the second phase. A large benefit of deforming two-phase materials is the homogenous nanocrystalline microstructure with smaller achievable grain sizes than in single phase materials subjected to HPT. Attention is given to development of hardness as a function of the applied strain, the chemical composition at different radii and the obtained microstructure. Tensile tests provide additional information about strength.

In the present work the harmonic structure design has been successfully applied for achieving a combination of high strength and high ductility, simultaneously, in a two-phase steel. The compacts of two-phase stainless steels with harmonic structure were prepared by controlling mechanical milling (MM) of pre-alloyed stainless steel powders followed by spark plasma sintering. The controlled MM leads to the formation of severely deformed "shell" region, wherein the subsurface region in the immediate vicinity of the powder surface consists of a nanocrystalline structure followed by the inner region consisting of dislocation cell structure. These severely deformed regions form fine-grained network during subsequent sintering, resulting in Harmonic structure. This networked structure displayed high strength, high ductility, and better uniform plastic deformation as compared to the homogeneous fine/coarse grained structure. Such a unique combination of properties in the two-phase stainless steel powder compacts was found to be associated with the ability of the harmonic structure to evenly distribute the strain during plastic deformation.

Fe₄₀Co₆₀ powders were produced by mechanical Alloying (MA) route. Structural and microwave dielectric properties were investigated. Discussion of obtained results is conducted according to milling time. X-Ray powder Diffraction (XRD) shows that disordered α (Fe₄₀Co₆₀) solid solution of substitution with body centered cubic (bcc) lattice is formed after 2h milling. Halder Wagner analysis reveals that least grain size of 15.59 nm and residual strain up to 0.8% are reached after 60h milling. The evolution of the Voigtian mixing factors according to milling progression confirms that structural properties are governed by residual strain accumulated during high- energy mechanical alloying (Gaussian profiles). Scanning Electron Microscopy (SEM) indicates that obtained powders adopt flattened angular shapes with high surface area. Microwave measurements are undertaken on bulk samples. High values of the dielectric permittivity depicting the conductive behavior of Fe-Co powders are measured. Dielectric permittivity spectra according to milling time shift towards higher values. Enhancement of the dielectric properties is related to the developed structure after milling.

The harmonic-structured composite that consists of a network fine grain region with a high speed steel and a dispersed coarse grain region with a low carbon steel was fabricated prepared using a mechanical milling, which is one of the severe plastic deformation method, and spark plasma sintering process. The microstructure and mechanical properties harmonic- structured composite compact were evaluated by a scaning electron microscope and a tensile test, respectively. The harmonic-structured composite exhibited high strength and enough ductility compared with a conventional particle-dispersed composite with the same weight ratio of high speed steel/low carbon steel. The microstructure observation of harmonic-structured composite revieals that the superior elongation of the harmonic-structured composite is attributed to the plastic deformation around the cracks which initiate at the network area.

Ti-6Al-4V alloy is an advanced structural material having applications in a wide range of areas spanning from biomedical to aerospace sectors due to the excellent combination of mechanical and chemical properties. In the present work, a new tailored heterogeneous microstructural design with a specific topological distribution of fine and coarse grained areas, called "harmonic structure", has been proposed for the strengthening of Ti-6Al-4V alloy to achieve improved performance of the components in service. It has been demonstrated that Ti-6Al-4V alloy with harmonic structure can be successfully prepared via a powder metallurgy route consisting of controlled severe plastic deformation of pre-alloyed powders via mechanical milling followed by their consolidation. The Ti-6Al-4V compacts with harmonic structure design exhibited significantly better strength and ductility, under quasi-static as well as rapid loading conditions, as compared to their homogeneous fine and coarse grained counterparts. It was found that the harmonic structure design has the ability to promote the uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding localized plastic instability.

The Ti-Al alloy/pure Ti harmonic-structured composite was produced by mechanical milling and spark plasma sintering process for improvement of low ductility at room temperature of Ti-Al alloy. The harmonic-structured composite with the dispersed area having coarse grained titanium and the network area having fine-grained Ti-48mol%Al alloy demonstrates high strength and high ductility at room temperature. The annealing effect of the microstructure on the mechanical properties in the Ti-Al alloy/pure Ti harmonic-structured composite are investigated. The microstructure of the Ti-Al alloy/pure Ti harmonic-structured composite annealed at 873K, 973 K and 1073 K are maintained the Ti-Al network structure and pure Ti dispersed regions, the average grain size of pure Ti dispersed region is only coarsen by annealing. The harmonic-structured composite annealed at 873K, 973K and 1073 K are maintained the high hardness. The tensile results reveal that the Ti-Al alloy/pure Ti harmonic- structured composite annealed at 873K exhibits high strength and especially high ductility.

High Pressure Torsion (HPT) experiments were performed for consolidation of water-atomized pure iron powder (99%) with initial particle sizes of 20-100 gm. The experiments were carried out successfully at room temperature, achieving both low level of residual porosity and significant grain refinement, thanks to the intense shear strain and hydrostatic pressure applied in HPT. X-ray diffraction analysis was carried out on the consolidated samples which revealed no significant proportion of oxides. Considering the inherent heterogeneity of the imposed shear strain in HPT, different positions across the diameters of sample disks were selected for mechanical property and microstructure investigations. The effect of shear deformation on the microstructure and texture was investigated by metallography, scanning electron microscopy, electron backscattered diffraction (EBSD). The micro-hardness and porosity of the samples as a function of shear strain at constant hydrostatic pressure were also measured. The grain size distributions showed homogeneous microstructures with significant grain refinement due to shear deformation. The texture measurements revealed that a shear texture typical to the shear of bcc iron was obtained during HPT compaction of iron powder.

The majority of methods of severe plastic deformation (SPD) used for producing ultra-fine grained (UFG) and nano materials involve the non-uniform distribution of strains in the workpiece. To make the refinement of grains uniform, interlinked operations are used in which either the orientation of the workpiece or the type of SPD is changed in some sequence. Each operation has its own set of control parameters affecting the output result. As a result, the optimization of the total chain of operations becomes very difficult, especially taking into account that each stage of material processing comes from the previous one with a certain non-uniformity of the structure. To deal with such types of problems the capability of tracing the transformation of the microstructure and accounting for its effect on mechanical properties in finite element modeling (FEM) is required. There are a number of detailed physical models of grain refinement and texture formation, but very often they are too complicated for practical engineering simulations. The mechanics of SPD are also studied and simulated in many works, but normally it is assumed that material is uniform, isotropic and its properties don't change during deformation. In this paper a microstructurally-coupled FE model of the SPD process is proposed. The question of selection and verification of macroscopic and microscopic constitutive relations is discussed. The results of a simulation made in QForm are analyzed and compared with some initial experimental data.

We have performed numerical simulations for the early stages (till several tens of microseconds) of dynamical channel angular pressing (DCAP). New dislocation and twinning models have been used for description of the kinetics and dynamics of defect structures; these models are described in the paper. In DCAP of copper with the initial sample velocities ranging from 100 m/s to 250 m/s we have found that the shock wave propagation leads to appearance of microscopic shear bands, its growth and intersections. We suppose that it is the main mechanism of the nanocrystalline grain formation. Twinning takes place in DCAP and the volume fraction of twins can go up to 0.5. It can be supposed that the shear bands and twins formation at the early stages of DCAP leads to some special features of the microstructure, which differs these structures from the structures obtained after quasi-static ECAP processes.

In this paper, the upper-bound solutions proposed by Eivani and Karimi Taheri [Comp. Mater. Sci. 42 (2008) 14] to calculate processing force and evaluate die corner angle Ψ formation in terms of tribology and die configurations during cold single pass equal channels angular pressed metals with constant flow stress were extended to work-hardening metals processed by two passes according to route A by using the Swift model combined to von Mises isotropic plasticity criterion. Also, adiabatic heat equation was coupled to solutions to express the final temperature of the workpiece. For that, thermomechanical properties of a hot-dip galvanized interstitial-free (IF) were considered and its behavior under pressing was evaluated to non-hardening and work-hardening conditions in all performed analyses. By including work-hardening in the models and for the critical friction factor of 0.4, theoretical predictions after single pass showed a decreasing of die corner angle and pressing force predictions and increasing of effective plastic strain and end temperature for all friction conditions and tooling geometries evaluated. In addition, after second pass, these responses showed higher values. Finally, with the proposed upper-bound models it was possible to analyze the dependency of angle Ψ, effective plastic strain, pressing load and sample temperature with the instantaneous workpiece height at the entry surface of deformation zone.

The high-pressure torsion (HPT) experiments have been investigated numerically. An axisymmetric model with twist was developed with commercial finite element software (Abaqus) to study locally the specificity of the stress and strain history within the transformed layers produced during HPT processing. The material local behaviour law in the plastic domain was modelled. A parametric study highlights the role of the imposed parameters (friction coefficient at the interfaces anvil surfaces/sample, imposed pressure) on the stress/strain distribution in the sample bulk for two materials: ultra-high purity iron and steel grade R260. The present modelling provides a tool to investigate and to analyse the effect of pressure and friction on the local stress and strain history during the HPT process and to couple with experimental results.

The stress-strained state (SSS), contact and force parameters of a new SPD technique – Multi-ECAP-Conform – have been studied. The new technique ensures a high level of accumulated strain □=4...5 per one processing cycle. Physical and computer modeling by finite element method in Deform-3D software was applied to evaluate the parameters. It is shown that the results of physical and computer modeling correlate with each other. Equipment has been upgraded, and experimental samples of Al-Mg-Si system alloy have been processed.

Surface nanocrystallization (SNC) was shown to be an effective approach to bypass the challenges of synthesizing bulk nanocrystalline material (NC) and yet to harvest its potential advantages. In this study unusual coverage (high number of impacts) was simulated for air blast shot peening process to induce SNC. The process is called severe shot peening. While the body of knowledge is mainly experimental in similar processes such as ultrasonic shot peening or surface mechanical attrition, a multi-scale scheme was developed to discuss the possibility of refinement from micro to nano-regime. The numerical framework combines finite element simulation of peening process with the dislocation density model. The result affirms the possibility of adopting air blast shot peening to induce surface nanocrystallization using typical media size, typical impact velocity and high coverage. This is an attempt to move from conventional shot peening toward severe shot peening to obtain surface nanocrystallization.

Durability of engineering workpieces surfaces is well-known to be strongly related to the microstructural evolutions induced by machining processes. One current challenge is to choose the right process parameters, such as the sliding speed, in order to optimize both the subsurface microstructure and the surface properties. In this paper, a special tribometer, able to simulate contact pressures and cutting speeds occurring during machining, has been used to characterize the effect of sliding velocity on microstructural evolution induced in copper. Significant recrystallization and grain refinement phenomena have been observed for the highest sliding speed tested (250m/min). Finite element analysis have been performed to extract local variables near the pin/copper bar interface. A good agreement is noticed between the equivalent plastic strain level, the temperature rise, the resulting grain size and the hardness gradient.

A computationally efficient procedure for modelling of microstructural changes on complex and spatially nonuniform deformation paths of severe plastic deformation (SPD) is presented. The analysis follows a two-step procedure. In the first step, motivated by saturation of material hardening at large accumulated strains, the steady-state kinematics of the process is generated for a non-hardening viscoplastic model by using the standard finite element method for a specified SPD scheme. In the second step, microstructural changes are investigated along the deformation-gradient trajectories determined in the first step for different initial locations of a material element. The aim of this study is to predict texture evolution and grain refinement in a non-conventional process of cold extrusion assisted by cyclic rotation of the die, called KOBO process, which leads to an ultra-fine grain structure. The texture evolution is calculated for fcc and hcp metals by applying crystal visco-plasticity combined with the self-consistent scale transition scheme. In parallel, by applying the simplified phenomenological model of microstructure evolution along the trajectories, grain refinement is modelled. The results are compared with available experimental data.

High-pressure torsion (HPT) is a metal-working technique used to impose severe plastic deformation into disc-shaped samples under high hydrostatic pressures. Different HPT facilities have been developed and they may be divided into three distinct categories depending upon the configuration of the anvils and the restriction imposed on the lateral flow of the samples. In the present paper, finite element simulations were performed to compare the flow process, temperature, strain and hydrostatic stress distributions under unconstrained, quasi-constrained and constrained conditions. It is shown there are distinct strain distributions in the samples depending on the facility configurations and a similar trend in the temperature rise of the HPT workpieces.

The Al 5xxx alloys are widely used in form of sheets in marine, transport, and chemical engineering and, thus, they are often have to undergo hot/cold rolling as the final metal forming operations. Recent investigations have demonstrated that ultra-fine grained (UFG) Al 5xxx alloys have a significant potential for industrial applications due to their improved mechanical properties and enhanced corrosion resistance. However, the development of hot/cold rolling routes for the UFG Al alloys is very time consuming due to numerous experimental trials and very expensive due to higher cost of the UFG processed materials. In this work, physical simulation of cold rolling is applied to the UFG Al 5083 alloy obtained via equal channel angular pressing with parallel channels to analyze the effect of cold rolling on the microstructure and microhardness of the material. The cold rolling parameters are chosen based on the outcomes of physical simulation and the UFG Al 5083 alloy is successfully subjected to cold rolling resulting in superior mechanical strength of the material. It is concluded that physical simulation can significantly increase the efficiency of experimental work on development of thermo-mechanical processing routes.

The principle of achieving high strength and superior properties in metal alloys through the application of severe plastic deformation has been exploited in the metal processing industry for many decades. In this contribution finite element simulations are presented of the HPT process. As opposed to most studies in literature, in which rigid sample holders are considered, the real elasto-plastic behavior of the holders is modeled. The simulations show that during the compression stage, plastic deformation occurs in the holders: initially, at the outside boundary of the sample cavity and, at a later stage, underneath the centre of the sample. The latter region of plastic deformation is rapidly growing and has a non-negligible effect on the response of the sample. Major conclusion is that the sample holders, and more specific, their deformability is key for the conditions in the specimen. Indeed, it severely affects important parameters for both the microstructural changes in the sample material, such as the amplitude and distribution of the hydrostatic stress, and its final shape.

Dual equal channel lateral extrusion (DECLE) is a type of equal channel angular pressing which employs T-shaped die instead of L-shaped die. In the present work, deformation behavior in the DECLE process is analyzed by using DEFOEM-2D. The effect of friction between the die channels and the specimen on the effective strain distribution homogeneity and load were investigated. The friction induces inhomogeneous deformation in the head, top and bottom regions of the work piece. As friction increases, the top gap becomes smaller and the strain distribution becomes more homogenous, but the maximum load value increases. These results can serve as a design for reasonably technological parameters for DECLE processing.

High pressure torsion (HPT) is an efficient technique of producing ultrafine grained materials with exceptional small grain size. In this study, a crystal plasticity finite element method (CPFEM) model has been developed to investigate the plastic deformation behavior of pure aluminum single crystal during the HPT process. The simulation results show that, the distribution and evolution of the macroscopic plastic strain and the accumulative shear strain are similar. The value increases with the increase of the distance from the center as well as the number of revolution. The simulation is capable of reflecting the anisotropic characteristics of HPT deformation, a non-homogenous deformation along the circumference of the sample could be observed. At the early stage of HPT deformation, the critical resolved shear stress (CRSS) along the radial direction presents a rapid increase, followed by a moderate increase and then reaches the near-saturate state. As the HPT deformation proceeds, there is a relatively weak increase in the quasi-saturate value and the near-steady region expands gradually towards the sample center. The orientation changes during the HPT process with increasing applied strain predicted by the developed CPFEM model are also presented.

In the present study, the effect of geometric parameters on the simple shear extrusion (SSE) process as one of the most recent severe plastic deformation methods is investigated. Three deferent curvatures for deformation channel based on linear, quadratic and sine equations are introduced. Simulation of the process is carried out by means of the commercial finite element code ABAQUS/Explicit. Effect of die profile as well as backpressure on the strain, strain rate and load of deformation is studied. Results show that the shape of die profile does not have any significant effect on the required backpressure and the load of the process. The most homogeneous distribution of strain is obtained by linear die profile. Among all die profiles, only the linear profile can provide a constant strain rate. It is shown that linear profile is also the best candidate for deformation channel in SSE process due to its feasibility and homogeneity in the distribution of stain and constant strain rate.

This paper is about the conception, design and realization of a new unique ECAP system with application of back-pressure and intensive ultrasound energy. 3D finite element calculations were used for finding the best construction configurations. The new unique ECAP equipment is used for deforming metallic samples with dimensions of 12x12x100 mm to obtain homogenous deformation in the whole specimen. The basic technical parameters of the equipment are: angle of channel intersection Φ = 90°, rounding angle Ψ = 0°, die heating system up to 400°C, punch heating system up to 300°C, computer controlled back pressure up to 1400 MPa, Emerson Branson ultrasonic energy system up to 4kW, longitudinal ultrasound amplitude up to 30 pm, water cooling system, flexible die geometry (channel inner radius can be changed), adaptive computer drive and control.

The logarithmic "equivalent" strain is frequently recommended for description of the experimental flow curves determined in high pressure torsion (HPT) tests. Some experimental results determined at -196 and 190 °C on a 2024 aluminum alloy are plotted using both the von Mises and logarithmic equivalent strains. Three types of problems associated with use of the latter are described. The first involves the lack of work conjugacy between the logarithmic and shear stress/shear strain curves, a topic that has been discussed earlier. The second concerns the problems associated with testing at constant logarithmic strain rate, a feature of particular importance when the material is rate sensitive. The third type of problem involves the "history dependence" of this measure in that the incremental logarithmic strain depends on whether the prior strain accumulated in the sample is known or not. This is a difficulty that does not affect use of the von Mises equivalent strain. For these reasons, it is concluded that the qualifier "equivalent" should not be used when the logarithmic strain is employed to describe HPT results.

One of available ways to enhancing the efficiency of production of sections is combining the CONFORM continuous extrusion process and the ECAP method. This paper describes the initial experience with such a combined process deployed in the CONFORM 315i machine, which is equipped with a specially-designed die chamber. Process trials were performed to explore the effects of the set-up of the CONFORM equipment on the resulting microstructure of Ti wire. The feedstock was in the form of CP Ti grade 2 bars of 10 mm diameter. Crucial parameters of the process include the temperature of the die chamber, which was purposefully varied from the initial 500 °C to the final 200 °C, and the cooling stage, which was realized immediately upon the exit from the die chamber. The mean grain size, mechanical properties and thermal stability were measured and studied in the specimens upon forming. The smallest grain size was achieved by two passes at 200 °C.

This report presents main achievements of R&D activities of the Institute of Physics of Advanced Materials of Ufa State Aviation Technical University (IPAM USATU, Ufa, Russia) with a special attention to innovative potential of nanostructured metals and alloys produced by the severe plastic deformation (SPD) techniques. Several examples of the first promising applications of bulk nanostructured materials (BNM) as well as potential competing technologies are considered and discussed. The authors would like to focus special emphasis on international cooperation in view of numerous emerging projects as well as different conferences and seminars that pave the way to close and fruitful cooperation, working visits and exchange of young scientists. The possibilities of international cooperation through various foundations and programs are considered.

The effect of the deformation processes on yield stress, Vickers microhardness and dislocation density were investigated using commercial purity (A1050) and alloyed aluminum (Al 6082). For the evolution of the dislocation density X-ray line profile analysis was used. In the large plastic strain range the variation of mechanical and microstructure evolution of A1050 and of Al 6082 processed by equal channel angular pressing are investigated using route BC and route C. In the plastic strain range up to 3 plane strain compression test was used to evaluate mechanical properties. The hardness and the yield stress showed a sharp increase after the first pass. In the case of A1050 it was found that the two examined routes has not resulted difference in the flow stress. In the case of Al 6082 the effect of the routes on the yield stress is significant. The present results showed that in the comparable plastic strain range higher yield stress values can be achieved by plane strain compression test than by ECAP.

The problems of temperature increase during high-pressure straining and equivalent strain calculation are reassessed on the basis of general considerations and experimental evidence. Temperature evolution is measured for some pure fcc and hcp metals (Cu, Al, Ni, Ti and Zr) and different regimes of HPT (pressure, strain accumulated and strain rate). The results obtained are compared with modelling and theoretical estimates. A simple model taking into account microstructure evolution during HPT is applied in order to explain the consequent "straining-hardening-softening". The heat release of plastic work is calculated on the basis of both the von Mises and Hencky equivalent strains giving some assessment on the applicability of these equations.

Metastable austenite in a Fe-24Ni-0.3C (wt.%) alloy was processed by high-pressure torsion and subsequently heat-treated. The HPT-processed material had lamellae structures composed of highly deformed austenite and deformation-induced martensite. The reverse transformation of the deformation-induced martensite and recovery/recrystallization of the retained austenite completed above 500 °C and resulted in fully annealed and single-phase austenite with different grain sizes. The ultrafine-grained and nanocrystalline austenite showed high yield strength and large ductility due to transformation-induced plasticity.

The influence of deformation temperature and strain rate on the mechanisms of elongated fine grain (EFG) formation in the medium-carbon steel was studied. Compression tests were carried out at the temperatures in range of 673-973K at three different strain rates: 10⁻², 1.3*10⁻³ and 10⁻⁴ s⁻¹. Presence of two temperature intervals with different dominant mechanisms of deformation was identified: low temperature (673-823K) interval and high temperature (873-973K) interval. Microstructure evolution during deformation at strain rate of 1.3*10⁻³ s⁻¹ and different temperatures was studied. Also was investigated the microstructure and mechanical properties of steel after warm plastic deformation. EFG structure formation in steel by caliber rolling at temperatures 673 and 773K on strain ε ~ 1.1 results in a significant increase of toughness, including at low temperatures, while improving strength.

Commercial interstitial free steel was processed by high pressure torsion (HPT) at room temperature up to 5 revolutions. HPT resulted in strong grain refinement. The microstructure after HPT was inhomogeneous with refined grains mainly in regions near the specimen periphery, while coarse only slightly fragmented grains were observed in specimen centre. The microstructure inhomogeneity was continuously smeared out with increasing number of rotations by extending the fine grain region from specimen periphery towards its centre. However, even after 5 revolutions the microstructure remained inhomogeneous characterized by slightly coarser grains in central regions as compared to peripheral regions of the specimen. Positron annihilation spectroscopy (PAS) and X-ray line profile analysis (XLPA) were employed to characterize the structure inhomogeneity in individual specimens. Microstructure and dislocation density evolution were correlated with mechanical properties characterized by a detail microhardness measurement throughout the individual specimens.

The paper deals with two-stage processing of medium-carbon steel 45 (0.45 % C; 0.27 % Si; 0.65 % Mn) via quenching and high pressure torsion. Such processing combination allowed producing a nanocomposite microstructure with a ferrite matrix and high-dispersed carbides. The ultimate tensile strength of the nanostructured steel is over 2500 MPa. The processing effect on the structure, mechanical properties and failure mechanisms of steel 45 samples is studied. The peculiarities of static fractures in the samples after HPT are demonstrated in comparison with those after quenching.

Twinning is an alternative mechanism to achieve ultra-fine grain structures through severe plastic deformation. The properties induced in a plastically deformed material are highly dependent on the degree of deformation, accumulated deformation energy and details on grain sizes and microstructure, which are on the scale of some tens of nanometers; therefore it is very important to understand misorientation distributions and dislocation arrays developed in the samples. In this work an F138 austenitic stainless steel was solution heat treated, deformed by Equal Channel Angular Extrusion (ECAE) at room temperature up to four passes, and rolled up to 70% thickness reduction at room temperature. The microstructure evolution was analyzed by x-ray diffraction and domain sizes calculated by Convolutional Multiple Whole Profile (CMWP) model, the misorientation boundaries were measured by electron backscattered diffraction (EBSD), and transmission electron microscopy. Mechanical behavior was tested by tensile tests.

This work is devoted to the creep-resistant AX41 magnesium alloy (Mg-4 wt.% Al-1 wt.% Ca), processed by extrusion and consecutive Equal Channel Angular Pressing (EX- ECAP) up to total of eight passes, via route A, Bc and C at 220 °C. Beyond the deformation behavior the change of the microstructures was studied by electron back-scattering and X-ray diffraction methods. Significant grain refinement was found for all processing routes (grain sizes decreased below 1 pm after 8 passes). The X-ray line profile analysis performed by Convolutional Multiple Whole Profile (CMWP) fitting method has not revealed differences between the particular dislocation structures. Route A was found to be the most effective processing route from the point of view of grain size refinement and the room temperature strength. The influence of the texture and the dislocation structure on the plastic deformation processes is discussed in detail.

Modeling the effect of deformation on mechanical properties of a Fe-23Mn-0.3C- 1.5Al (in wt. %) TWIP steel subjected to extensive cold rolling was performed. The approach including Hall-Petch relation and dislocation strengthening was used for the determination of the strength increment with deformation. Distance between twin boundaries was considered to be the mean free path for dislocation glide in the Hall-Petch relationship. The rate of dislocation accumulation in the TWIP-steel was calculated via the X-ray diffraction (XRD) measurements and compared with direct transmission electron microscopy (TEM) measurements by counting individual dislocations crossing the thin foil surface after small reductions. It was shown that a decrease of the dislocation mean free path by formation of twins with nanoscale thickness is of less importance for the strengthening than an increase of the dislocation density, which was shown to be the major strengthening mechanism. This suggested that twin boundaries were more readily transparent and, therefore, provided less strengthening as compared to ordinary grain boundaries. The developed model has shown a good agreement with the experimental data.

The formation of ultrafine-grained structures was studied in a 316L stainless steel during severe plastic deformation. The steel samples were processed up to a total amount of strain of 4 at ambient temperature using two different methods, i.e., multidirectional forging and unidirectional bar rolling. The large strain developed upon cold working resulted mechanical twinning and partial martensitic transformation. The latter was readily developed during multidirectional forging. After straining to the total amount of strain of 4, the austenite fractions comprised approximately- 0.45 as well as 0.15 in the rolled and forged samples, respectively. Both the multidirectional forging and bar rolling led to extensive grain refinement. The uniform microstructures consisting of austenite and ferrite crystallites with the transverse size of 60 nm and 30 nm were evolved at a total amount of strain of 4 in the rolled and forged samples, respectively. The grain refinement by severe plastic deformation was accompanied by an increase for the microhardness to 5380 and 4970 MPa for the forged and rolled samples, respectively.

This paper introduces a new method of forming for achievement of grain structure refinement by processing in DRECE (Dual Rolls Equal Channel Extrusion) equipment. The DRECE device was developed at the VSB – Technical University of Ostrava. It allows grain refinement in strip plate with dimensions of 58 mm (width) × 2 mm (thickness) × 1000 mm (length). The influence of the number of passes on the mechanical properties and related structure refinement was examined experimentally. The effect of a heat treatment (500 °C/1 h/steady air) on the grain refinement of low carbon steel after severe plastic deformation is analysed. Through this novel technique, the grain structure can be converted into a submicron grain structure.

The nano-grained (NG) high-Mn austenitic steel with average grain size of 60 nm and the ultrafine-grained (UFG) steels with grain size below 500 nm are successfully produced by combination of the asymmetric rolling (ASR) and symmetric rolling (SR) method and the subsequent annealing treatment. The annealed NG steels exhibit relatively higher strain hardening and good balance of strength and ductility, which is attributed to the partial recrystallization of the nanostructures and the relatively lower stacking fault energy of the high-Mn TWIP steel.

The mechanical behavior of a chromium-nickel austenitic stainless steel with submicrocrystalline structures produced by multidirectional forging (MDF) to a total strain of ~ 4 at temperatures of 700 and 600°C was studied. This processing resulted in the formation of uniform ultrafine grained structure with an average crystallite size of 360 and 300 nm, respectively, and high dislocation density. The tensile tests were carried out in a wide temperature range 20-650°C. At ambient temperature, the yield stress (YS) comprised 900 MPa and 730 MPa in the samples subjected to MDF at 600 and 700°C, respectively. It should be noted that this strength was achieved along with elongations of 16% and 22% in the samples subjected to MDF at 600 and 700°C. The YS decreased and elongation-to-failure tends to increase with increasing test temperature and approaching 235 MPa and 51%, respectively, at 650°C. Effect of temperature on mechanical behavior of stainless steel with submicrocrystalline structure is discussed.

The effect of cold rolling on the microstructure evolution and mechanical properties of a cold rolled Fe-0.3C-17Mn-1.5AI TWIP steel was studied. The plate samples were cold rolled with reductions of 20, 40, 60 and 80%. The structural changes were associated with the development of deformation twinning and shear bands. The average spacing between twin boundaries in the transverse section of the rolled plates decreased from ~190 to 36 nm with an increase in the rolling reduction from 20 to 40%. Upon further rolling to 80% reduction the twin spacing remained at about 30 nm. The cold rolling resulted in significant increase in strength as revealed by tensile tests at an ambient temperature. The offset yield stress approached 1440 MPa, and the ultimate tensile strength increased to 1630 MPa after rolling reduction of 80%. Such significant strengthening was attributed to the development of specific structure consisting of deformation nanotwins with high dislocation density.

The microstructure of an oxide dispersion strengthened ferritic PM2000 steel with a strong initial (100) texture has been investigated after compression by dynamic plastic deformation (DPD) at room temperature to a strain of 2.1. Measurements using electron backscatter diffraction and transmission electron microscopy indicate that DPD along the (100) direction results in a lamellar-type microstructure, in which lamellae of the (100) orientation alternate with (111) lamellae. These lamellae have a common rotation (110) axis in the compression plane. The microstructure is quite heterogeneous, where regions containing very narrow lamellae (with (111) lamellae as narrow as 20-40 nm) and regions of comparatively broad lamellae are found.

The article focuses on the severe plastic deformation (SPD) of low carbon steel AISI 1010 performed at increased temperature. The grain refinement of ferrite structure is monitored and described with respect to different initial steel structure modified by thermal and thermomechanical (TM) treatment (TM) prior severe plastic deformation. The refinement of coarse initial ferrite structure with grain size in range of 30 – 50 gm resulted from solutioning was conducted then in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process and quite uniform ferrite structure with grain size of the order of gm was obtained. The further grain refinement steel structure was then accomplished during warm Equal Channel Angular Pressing (ECAP ϕ = 120°) at 300°C, introducing different strain in range of ε_ef = 2.6 -4. The change of microstructure in dependence of the effective strain was evaluated by SEM and TEM study of thin foils. The high straining of steel resulted in extensive deformation of ferrite grains and formation of mixture of submicron grains structure in banded deformed structure with dense dislocation network and subgrains. The dynamic polygonization process, due to increased ECAP temperature, modified the submicrocrystalline structure formation. There was only indistinctive difference observed in structure refinement when considering different initial structure of steel. The tensile behaviour was characterized by strength increase followed by softening. None work hardening phenomenon appeared at tensile deformation of deformed bars.

Applying a continuous equal channel angular pressing technique (ECAP-Conform), this work deals with the structure transformation and mechanical properties of a Grade 4 Ti. The microstructure evolution and mechanical properties were studied using electron backscatter diffraction; transmission electron microscopy and tensile tests. The results demonstrated that the microstructure evolution is ensured by the formation of low-angle deformation-induced boundaries during the initial stages of ECAP-Conform. With the number of ECAP-Conform passes increasing up to 10, a structure with an average grain size of 0.22 pm was achieved, and the ultimate strength increased 1.5 times higher with respect to the initial state.

This paper focuses on the study of the aging kinetics of the β-titanium Ti-15Mo alloy prepared by high pressure torsion. The experimental methods of differential scanning calorimetry and transmission electron microscopy were used for structural investigations. It was established that during aging at 500 and 550 °C, in the ultrafine-grained (UFG) alloy, the precipitating a-particles have mostly equiaxed morphology, in contrast to the needle-like and lens one in the coarse-grained (CG) alloy. There have been identified differences in the aging kinetics of the Ti-15Mo alloy in the UFG state identified by a decrease in microhardness within the first 30 minutes of heating, as opposed to the CG alloy coarsening. The influence of morphological features of the alloy microstructure on the strengthening effect after aging is discussed.

In the present research, the effects of high-pressure torsion (HPT) processing on the microstructure and mechanical properties of Ti-5Al-5Mo-5V-3Cr (Ti5553) alloy were studied. HPT processing produced a white etching layer (WEL) in the middle section of the cross-section and numerous shear bands in the surface region of the cross-section. And the thickness of the WEL increased with increasing the HPT revolutions. TEM observation of the WEL revealed an ultrafine-grained structure with high degree of lattice distortions. The mechanical properties measurements showed that the hardness and ultimate tensile strength increased by HPT processing, accompanied with a decrease in the elongation to failure. It is considered that the mechanical properties of HPT processed Ti5553 alloy are mostly dominated by the shear banded region and the WEL where have the finest grain size and high density of dislocations.

The influence of warm swaging on the structure and properties of Ti-6Al-4V alloy was studied. Warm swaging of the alloy in the interval 680-500°C with the total strain of ε=2.66 was found to be resulted in the formation of a homogeneous globular microstructure with a grain size of 0.4 μm in both longitudinal and transversal sections. Room temperature tensile strength and tensile elongation of the swaged alloy was 1315MPa and 10.5%, respectively. Ultrafine-grained Ti-6Al-4V alloy produced by swaging exhibited good workability at 600-700 °C.

Cylindrical samples of CP Titanium (Grade 2) were deformed by one, two and three passes of equal channel angular pressing (ECAP) each at temperatures 77, 300 and 575K, respectively. The microstructure of samples processed at 77K shows retardation of recrystallisation, high density of dislocations and deformation twins, diffuse and obscure grain boundaries compare to microstructure of samples processed at room and high temperature, where recrystallised ultrafine equiaxed grains are observed.

Mechanical properties for all structural states of Ti were studied by microhardness measurements at 300 K, and uniaxial compression at temperatures 300, 170, 77 and 4.2 K. Higher levels of ECAP deformation (more passes of ECAP) lead to higher values of strength and hardness at all studied temperatures. Decrease of ECAP temperature leads to increase of strength characteristics in all cases. Influence of ECAP and compression temperatures on possible changes of deformation mechanism is discussed.

Unique in-situ electric resistivity measurement was utilized to identify microstructural changes in ultra-fine grained commercially pure titanium and Ti-6Al-7Nb alloy. Both materials were prepared by equal channel angular pressing. Changes in resistivity evolution during in-situ heating were compared to scanning electron microscopy observations. Both materials are stable up to 440°C. Further heating at rate 5°C/min causes recovery and recrystallization of UFG structure. At 650°C the microstructure is fully recrystallized. High resolution in-situ electric resistivity measurement is capable of detecting recovery and recrystallization in UFG CP Ti and Ti-6Al-7Nb alloy.

Cycling of the compression pressure during high pressure torsion (HPT) of the titanium Ti-6Al-4V alloy significantly improves the grain refinement process, and also results in a more uniform microstructure along the sample diameter.

To clarify the grain size effect on mechanical property in fine grained pure Mg, mechanical properties of fully recrystallized Mg with fine grain sizes were investigated. The specimens having fully recrystallized microstructures with mean grain sizes of 2.8 μm and 7.8 μm were fabricated by HPT processing and subsequent annealing. The 2.8 μm specimen showed discontinuous yielding with a high yield stress and low strain hardening while the 7.8 μm specimen showed continuous yielding with a low yield stress and high strain hardening. The as-HPT processed specimen showed a larger ductility than that in the subsequently annealed specimens.

It was shown that multiaxial forging with continuous decrease of temperature from 450°C to 250°C turns coarse structure of the Mg-0.8Ca alloy in homogenized state with grain size of several hundreeds gm into fine structure with average grain size of about 2.1 gm. Refinement of structure is accompanied by drastic increase of mechanical properties: tensile yield strength increases from 50 MPa to 193 MPa, ultimate tensile strength increases from 78 to 308 MPa and elongation to fracture increases from 3.0% to 7.2%. The microstructural evolution during multiaxial forging is studied using optical microscopy, scanning electron microscopy and EBSD analysis. The mechanisms responsible for refinement of microstructure are discussed

Equal-channel angular pressing (ECAP) can produce ultrafine grain structures in metals. The processing can also dissolve second phases through mechanical alloying effects over the equilibrium solubility of alloying elements. Therefore, one can enhance mechanical properties by combining ECAP and subsequent precipitation treatment by proper aging. In this preliminary study, an AZ80 Mg alloy was investigated. The original extruded bars were subjected to ECAP at 473 K for 4 passes to achieve a significant grain refinement down to the submicrometric regime. The possibility of exploiting the aging effect to improve mechanical strength of the alloy was studied by the following two different methods. The first method consisted of ECAP processing the samples followed by aging. The second method consisted of performing a solution treatment prior to ECAP processing and then the final aging of the samples. Micro-hardness measurements and microstructure analyses showed that reprecipitation of the Mg₁₇Al₁₂ phase can occur during warm temperature ECAP and aging in the AZ80 alloy at grain cores in a more finely dispersed form. This precipitation behavior can potentially generate a significant contribution to the strength of the UFG alloy.

Friction stir processing (FSP) and equal channel angular pressing (ECAP) were used to modify the microstructure of twin roll cast (TRC) AZ31 magnesium. The influence of these processes on the microstructural properties of the material was investigated. It was found that both processes produced microstructures with an average grain size of less than 10 pm, suggesting that they have the potential for superplastic deformation. Heat treatments were performed on the TRC, ECAP and FSP materials to assess their microstructural stability. Both the ECAP and TRC material were found to be fairly stable, showing normal grain growth while the FSP material grew substantially at temperatures above 200°C. The activation energy of grain boundary motion of the TRC material was calculated to be 167 kJ/mol.

Microstructure investigation and microhardness mapping were done on the material with ultra-fine grained structure prepared by constrained groove pressing of twin-roll cast AZ31 magnesium strips. The microstructure observations showed significant drop of the grain size from 200 gm to 20 gm after constrained groove pressing. Moreover, the heterogeneities in the microhardness along the cross-section observed in the as-cast strip were replaced by the bands of different microhardness in the constrained groove pressed material. It is shown that the constrained groove pressing technique is a good tool for the grain refinement of magnesium alloys.

Al-Fe alloys are attractive for applications at temperatures beyond those normally associated with the conventional aluminum alloys. Under proper solidification condition, a full eutectic microstructure can be generated in Al-Fe alloys at Fe concentration well in excess of the eutectic composition of 1.8 wt.% Fe. The microstructure in this case is characterized by the metastable regular eutectic Al-Al₆Fe fibers of nano-scale in diameter, instead of the equilibrium eutectic Al-Al₃Fe phase. In this study, the microstructure and mechanical properties of the Al-3Fe alloy with metastable Al₆Fe particles deformed by equal channel angular extrusion were investigated. Severe plastic deformation results in a microstructure consisting of submicron equiaxed Al grains with a uniform distribution of submicron Al₆Fe particles on the grain boundaries. The room temperature tensile properties of the alloy with this microstructure will be presented.

The precipitation kinetics of Al-Cu alloys have recently been revisited in various studies, considering either the effect of severe plastic deformation (e.g., by equal-channel angular pressing – ECAP), or the effect of particle reinforcements. However, it is not clear how these effects interact when ECAP is performed on particle-reinforced alloys. In this study, we analyze how a combination of particle reinforcement and ECAP affects precipitation kinetics. After solution annealing, an AA2017 alloy (initial state: base material without particle reinforcement); AA2017 + 10 vol.-% Al₂O₃; and AA2017 + 10 vol.-% SiC were deformed in one pass in a 120° ECAP tool at a temperature of 140°C. Systematic differential scanning calorimetry (DSC) measurements of each condition were carried out. TEM specimens were prepared out of samples from additional DSC measurements, where the samples were immediately quenched in liquid nitrogen after reaching carefully selected temperatures. TEM analysis was performed to characterize the morphology of the different types of precipitates, and to directly relate microstructural information to the endo- and exothermic peaks in our DSC data. Our results show that both ECAP and particle reinforcement are associated with a shift of exothermic precipitation peaks towards lower temperatures. This effect is even more pronounced when ECAP and particle reinforcement are combined. The DSC data agrees well with our TEM observations of nucleation and morphology of different precipitates, indicating that DSC measurements are an appropriate tool for the analysis of how severe plastic deformation and particle reinforcement affect precipitation kinetics in Al-Cu alloys.

Aluminum Al-Cu-Mg alloy has been subjected to high pressure torsion (HPT) and equal-channel angular pressing (ECAP) at various temperatures. An ultrafine-grained (UFG) structure thermally stable up to a temperature of 175 °C was produced in all the investigated samples. Simultaneous increase in strength and ductility has been demonstrated in an ECAPed sample in comparison with a coarse-grained sample subjected to standard treatment.

Al-Cu-Mg alloys are extensively used for riveting applications in aerospace industries due to their relatively high shear strength coupled with high plasticity. The significant advantage of using V65 aluminum alloy ((Al-4Cu-0.2Mg) for rivet application also stems from its significantly slower natural aging kinetics, which gives operational flexibility to carryout riveting operation even after 4 days of solution heat treatment, in contrast to its equivalent alloy AA2024.Rivets are usually made by cold heading of wire rods. In order to form a defect free rivet head, grain size control in wire rods is essential at each and every stage of processing right from casting onwards upto the final wire drawing stage. Wire drawing is carried out at room temperature to reduce diameter as well as impart good surface finish. In the present study, different microstructures in V65 alloy bars were produced by rolling at different temperatures (room temperature to 523K) and subsequently deformed by equal channel angular pressing (ECAP) at 423K upto an equivalent strain of 7. ECAP was carried out to study the effect of initial microstructure on grain refinement and degree of deformation on the evolution of ultrafine grain structure. The refinement of V65 alloy by ECAP is significantly influenced by Initial microstructure but amount of deformation strongly affects the evolution processes as revealed by optical microscopy and transmission electron microscopy.

A concurrent strengthening process by high-pressure torsion (HPT) and fine precipitation hardening of an Al 2024 alloy has been studied. The HPT was conducted on disks of the alloys under an applied pressure of 6 GPa for 0.75 and 5 turns with a rotation speed of 1 rpm at room temperature. The HPT processing leads to microstructural refinement with an average grain size of ~240 nm and to an increase in hardness up to a saturation after 5 turns. Aging treatment is performed for sample after 5 turns at temperatures of 423 K for a maximum period up to 256 hours. The hardness increased above the hardness level after HPT processing through the subsequent aging. This study thus suggests that simultaneous hardening due to grain refinement and fine precipitation occurred by a combination of HPT processing and subsequent aging at 423 K.

A composite sheet of commercially pure aluminum and an Al-0.3 wt.% Sc alloy (in the supersaturated solid solution condition) was produced by accumulative roll bonding at 200°C. The material was then subjected to isothermal annealing at 300°C for 1-30 minutes and cold water quenched. The transverse section was investigated by electron back-scatter diffraction (EBSD) to investigate the variations in microstructure and texture within Al layers through the sheet thickness. A faster spheroidization of the highly elongated lamellar band deformation structures was observed in the surface aluminum layer as compared to the mid- and quarter-thickness layers. In the quarter thickness aluminum layer so-called continuous recrystallization occurred and, thus, the p-fiber rolling texture was retained. Further growth in this layer led to secondary recrystallization of cube orientations. In contrast, in the surface aluminum layers the recrystallization and grain growth texture were relatively random. Intermediate behavior was observed in the mid-thickness aluminum layer.

An aluminum-copper alloy (Al-2024) was successfully subjected to high-pressure torsion (HPT) up to five turns at room temperature under an applied pressure of 6.0 GPa. The Al-2024 alloy is used as a fuselage structural material in the aerospace sector. Mechanical properties of the HPT-processed Al-2024 alloy were evaluated using the automated ball indentation technique. This test is based on multiple cycles of loading and unloading where a spherical indenter is used. After two and five turns of HPT, the Al-2024 alloy exhibited a UTS value of ~1014 MPa and ~1160 MPa respectively, at the edge of the samples. The microhardness was measured from edges to centers for all HPT samples. These results clearly demonstrate that processing by HPT gives a very significant increase in tensile properties and the microhardness values increase symmetrically from the centers to the edges. Following HPT, TEM examination of the five-turn HPT sample revealed the formation of high-angle grain boundaries and a large dislocation density with a reduced average grain size of ~80 nm. These results also demonstrate that high-pressure torsion is a processing tool for developing nanostructures in the Al-2024 alloy with enhanced mechanical properties.

Aluminium alloys prepared by twin-roll casting method become widely used in industry applications. Their high solid solution supersaturation and finer grains ensure better mechanical properties when compared with the direct-chill cast ones. One of the possibilities how to enhance their thermal stability is the addition of zirconium. After heat treatment Al₃Zr precipitates form and these pin moving grain boundaries when the material is exposed to higher temperatures.

In the present work twin-roll cast aluminium alloys based on AA3003 with and without Zr addition were annealed for 8 hours at 450 °C to enable precipitation of Al₃Zr phase. Afterwards they were subjected to severe plastic deformation by equal channel angular pressing, which led to the reduction of average grain size under 1 μm. During subsequent isochronal annealing recovery and recrystallization took place. These processes were monitored by microhardness measurements, light optical microscopy and in-situ transmission electron microscopy. The addition of Zr stabilizes the grain size and increases the recrystallization temperature by 100 °C.

Recently it has been established that during high pressure torsion dynamic aging takes place in aluminum Al-Mg-Si alloys resulting in formation of nanosized particles of strengthening phases in the aluminum matrix, which greatly improves the electrical conductivity and strength properties. In the present paper structural characterization of ultrafine-grained (UFG) samples of aluminum 6201 alloy produced by severe plastic deformation (SPD) was performed using X-ray diffraction analysis. As a result, structure features (lattice parameter, size of coherent scattering domains) after dynamic aging of UFG samples were determined. The size and distribution of second- phase particles in the Al matrix were assessed with regard to HPT regimes. Impact of the size and distribution of the formed secondary phases on the strength, ductility and electrical conductivity is discussed.

In order to clarify the aging behavior in ultrafine grained (UFG) Al alloys, a commercial Al-Mg-Si alloy was severely deformed by accumulative roll-bonding (ARB) process and subsequently aged at 100°C or 170°C. The age-hardening behavior and microstructure change during aging were investigated. At 170 °C, age-hardening was observed in solution treated (ST) specimens, but solution-treated and ARB-processed specimens were not hardened by aging. On the other hand, the hardness of the both ST specimen and ARB-processed specimen increased by aging at 100°C. From TEM observation, it was found that the ARB- processed specimen had an ultrafine lamellar boundary structure and the structure was kept during aging at 170°C and 100°C. In the ST specimen aged at 170°C, fine precipitates were observed within coarse grains. In the specimen ARB-processed and subsequently aged at 170°C, coarser precipitates were observed within ultrafine grains and on grain boundaries. It was considered that the reason why the hardness of the specimens ARB-processed and subsequently aged did not increase was coarsening of precipitates. In the specimens aged at 100°C, obvious precipitates were not observed, but clusters Mg and Si seemed to form during the aging, leading to the increase in the hardness of the specimen. From the results, it was suggested that aging at low temperatures could improve mechanical properties of Al alloys through combining grain refinement and precipitation hardening.

In this paper dynamic strain ageing behavior in an Al-Mg-Si alloy related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation and ageing effects on microstructure evolutions and strengthening characteristics, the Al6061 alloy were subjected to ϕ=90° ECAP die for up to 4 passes via route Bc at high temperatures. For investigating the effects of ageing temperature and strain rate in ECAP, Vickers hardness tests were performed. The combination of the ECAP process with dynamic ageing at higher temperatures resulted in a significant increase in hardness. The microstructural evolution of the samples was studied using electron back-scattering diffraction (EBSD). The grains of Al6061 aluminum alloy were refined significantly at 100 and 150 °C with greater pass numbers and the distributions of grain size tended to be more uniform with pass number increasing. Frequency of sub-boundaries and low angle grain boundaries (LAGBs) increased at initial stage of deformation, and sub-boundaries and LAGBs evolved into highangle grain boundaries (HAGBs) with further deformation, which resulted in the high frequency of HAGBs in the alloy after ECAP 4 passes.

The present work aims to compare two processes: Accumulative Roll Bonding and Cross Accumulative Roll Bonding (CARB). Both processes consist in the repetition of rolling but the second technique adds a 90° rotation of the sheet around its normal direction between each rolling. Microstructure, mechanical properties and texture were compared for both processes on an AA5754/AA6061 composite. As a result a thinner and less elongated microstructure was obtained in the CARB process leading to an isotropy and an improvement of the mechanical properties. Besides, the texture was characterized by the rotated Cube component for both processes but for CARB it is of less strength.

Supersaturated Cu – 3 at.% Ag alloy was processed by rolling at liquid nitrogen temperature and subsequent annealing at 623 K up to 20 min. It was found that after annealing, an inhomogeneous solute atom distribution developed, since the Ag particles with small size and/or large specific interfacial energy were dissolved due to the Gibbs-Thomson effect. In the region where the solute concentration increased, a high dislocation density was retained in the Cu matrix even after annealing, while in the region where the Ag solute content did not increase, the dislocation density decreased by more than one order of magnitude. Therefore, in the cryorolled and annealed samples, heterogeneous microstructures were developed where both the dislocation density and the solute concentration varied considerably.

Cu-Ag alloys in three different compositions (Cu – 25/50/75wt% Ag) were produced by powder consolidation followed by high-pressure torsion. Deformation was performed till a saturation regime was reached. The generated microstructures were investigated by transmission electron microscopy and vary from ultra-fine grained to nanocrystalline to even partially amorphous structures. Vickers hardness measurements show a strong increase in hardness compared with the pure metals, annealing at 130°C leads to an additional increase in hardness.

Microstructure studies of Cu – 22 wt. % In alloy after annealing and severe plastic deformation were carried out by means of scanning and transmission electron microscopy. Two samples of the alloy were annealed at 350 °C and 520 °C for 553 hours and then subjected to high pressure torsion at room temperature under a pressure of 5 GPa in a Bridgman anvil-type unit. The sample annealed at 350 °C exhibited duplex microstructure: copper matrix with embedded plates of 8 phase (Cu₇In₃) and 8 phase with lamellar precipitates of copper. The microstructure of the sample annealed at 520 °C consisted of copper matrix with spherical precipitates of 8 phase. The subsequent severe plastic deformation resulted in a substantial grain refinement in copper matrix to nanoscale size. However, the morphology and size of 8 phase precipitates did not change. The measurements of microhardness and calorimetric studies were also performed in order to study the specific properties of 8 phase.

The effect of equal channel angular pressing at a temperature of 200 °C to a total strain of 12 on microstructure evolution and mechanical properties of a Cu-0.87wt.%Cr- 0.06wt.%Zr was investigated. New ultrafine grains resulted from gradual increase in the misorientations of strain-induced low-angle boundaries with increasing number of passes. Therefore, the development of ultrafine grains is considered as a kind of dynamic recrystallization. The equal channel angular pressing to a total strain of 12 resulted in the formation of almost equiaxed ultrafine grained structure with an average grain size of 0.5 dm and 0.7 dm in the solution treated and aged samples, respectively. At the same time, the fraction of ultrafine grains comprises 0.77 in the solution treated samples and 0.72 in the aged samples. Significant grain refinement led to the remarkable increase of the ultimate tensile strength up to 550 MPa.

Cu-18.2Zn-1.5Si-0.25Fe (mass%) alloy was heavily cold rolled. Ultrafine grained (UFGed) structure, containing a mixture of lamellar and mechanical twins, was easily and homogeneously formed. The average grain size was approximately 100 nm. The as-rolled sample showed quite high ultimate tensile strength (UTS) over 1 GPa. The UTS was higher than those obtained by multi directional forging. When the samples were annealed at relatively low temperatures between 553 K and 653 K, they showed slight hardening followed by large softening due to occurrence of static recrystallization (SRX). Annealing of UFGed structure at relatively low temperature of around 0.4 Tm caused extensive SRX that, in turn, induces ultrafine RXed grained structure. The grain size of the RXed sample was as fine as 200 nm. Although the annealing induced recovery of ductility while UTS gradually reduces, UTS over 1 GPa with ductility of 15 % were attained. The RXed grains mainly contained ultrafine annealing twins. Therefore, UFGed structure and superior mechanical properties could be achieved by a simple process of cold rolling, i.e., without severe plastic deformation.

In the present study the effect of severe plastic deformation by high-pressure torsion in liquid nitrogen on the structure of Cu, Ni and Nb and its thermal stability is analyzed. It is demonstrated that the room-temperature HPT of Cu is accompanied by its dynamic recrystallization. The latter can be suppressed if the deformation temperature is decreased to cryogenic, and the nanocrystalline structure can be obtained, but it degrades at room temperature due to the post-dynamic recrystallization. The HPT of Ni in liquid nitrogen results in nanocrystalline structure with average grain sizes of 80 nm and microhardness of 6200 MPa, this structure being stable at room temperature. In Nb subjected to low temperature HPT the average crystallite sizes are 75 nm, and the microhardness is 4800 MPa. The thermal stability of nanocrystalline structure in Ni and Nb, obtained by HPT in liquid nitrogen, is considerably lower than after the room temperature HPT. The grain growth starts in Ni at as low as 200°C and in Nb at 300°C. Thus, the HPT at cryogenic temperature enables to refine the structure and increase microhardness considerably, but the thermal stability of the as-obtained structures is quite low.

The microstructure evolution was investigated in a Cu-0.3%Cr-0.5%Zr alloy subjected to large plastic deformation at temperature of 400 °C. Two methods of large plastic deformation, i.e., equal channel angular pressing (ECAP) and multidirectional forging (MDF) were used. The large plastic deformations resulted in the development of new ultrafine grains. The formation of new ultrafine grains occurred as a result of continuous reaction, i.e., progressive increase in the misorientations of deformation subboundaries. The faster kinetics of microstructure evolution was observed during MDF as compared to ECAP. The MDF to a total strain of 4 resulted in the formation of uniform ultrafine grained structure, while ECAP to the same strain led to the heterogeneous microstructure consisting of new ultrafine grains and coarse remnants of original grains. Corresponding area fractions of ultrafine grains comprised 0.23 and 0.59 in the samples subjected to ECAP and MDF, respectively.

In current study the Cu-14%(wt.)Fe alloy was subjected to 1-10 ECAP passes via route A and, in addition, to 4 passes via routes Bc and C. Microstructure of the alloy after ECAP was characterized using SEM and EBSD analysis. It was shown that the refinement of Fe particles largely depended on the processing route: route A was the most efficient and route Bc was the less efficient. After 10 passes via route A the average thickness of Fe particles decreased to about 3 gm from about 10 gm in initial state. However, the microstructure development in Cu matrix was found to be not dependent much on ECAP route – the average grain/subgrain reached value of about 0.25 gm (according to EBSD analysis) after 4 passes. The mechanical properties of the alloy were also found to be not sensitive to ECAP routes. Ultimate tensile strength increased from 330 MPa in initial state to 545 MPa after 10 ECAP passes. Peculiarities of microstructural evolution of the alloy during ECAP as well as correlation between microstructure and mechanical properties are discussed.

Several elements were processed by high-pressure torsion and phase transformations were investigated. Titanium exhibited a transition from hcp to an ω phase at pressures higher than 4 GPa, while the transition was facilitated with increasing the shear strain. The stability of ω phase appeared to decrease with decreasing the grain size to the nanometer level (e.g., by processing at cryogenic temperatures and/or by consolidation of powders). Cobalt exhibited a transition from metastable fcc to hcp until the grain size reached the submicrometer level, but the fcc phase appeared to be more stable with decreasing the grain size to the nanometer level. Graphite exhibited a transition to diamond-like carbon (DLC), while the formation of DLC was facilitated with increasing the pressure, temperature and strain.

A body-centred cubic (BCC) structure metal, tantalum, was processed by high- pressure torsion (HPT) at room temperature with different numbers of rotations. The microstructural evolution was studied by electron backscatter diffraction (EBSD). The grain sizes were significantly refined at the disk edge area in the early stages of deformation (N = 0.5) but tended to attain saturation after the numbers of rotations was increased to N = 5. As the deformation continued, some coarse grains appeared in the disk edge areas and it appeared that there was structural recovery at the expense of grain boundary migration in the tantalum during HPT processing. Microhardness measurements showed the hardness gradually evolved towards a more homogenized level across the disk surfaces as the numbers of rotations increased. The hardness level after N = 10 turns was slightly lower than after N = 5 turns, thereby indicating the occurrence of a recovery process after 5 turns.

Severe plastic deformation (SPD) is an attractive processing method for refining microstructures of metallic materials to give ultrafine grain sizes within the submicrometer to even the nanometer levels. Experiments were conducted to discuss the evolution of hardness, microstructure and strain rate sensitivity, m, in a Zn-22% Al eutectoid alloy processed by high- pressure torsion (HPT). The data from microhardness and nanoindentation hardness measurements revealed that there is a significant weakening in the Zn-Al alloy during HPT despite extensive grain refinement. Excellent room-temperature (RT) plasticity was observed in the alloy after HPT from nanoindentation creep in terms of an increased value of m. The microstructural changes with increasing numbers of HPT turns show a strong correlation with the change in the m value. Moerover, the excellent RT plasticity in the alloy is discussed in terms of the enhanced level of grain boundary sliding and the evolution of microsturucture.

The effect of high pressure torsion (HPT) on the microstructure evolution of Cu-Fe 36% wt alloy has been studied. The initial Cu-Fe alloy has a dendritic structure, the length of dendrites is up to 100 gm. As a result of HPT (20 anvil rotations at 400 °C) the refinement of a- Fe dendrites occurs, and a microstructure with Fe inclusions with a size from 0.1 to 5 gm uniformly distributed in the copper matrix forms. Subsequent annealing at 700 °C for 1 hour results in some coarsening of a-Fe particles, as compared to the state after HPT. However, the dendritic structure typical of the cast alloy does not recover; it remains dispersed with a size of a-Fe particles less than 20 gm. As a result of HPT the alloy microhardness increased from 1800 to 4000 MPa. The subsequent annealing at T = 700 °C decreased the microhardness to 2700 MPa, but this value is 1.5 times higher than that in the initial as-cast state.

Several nanostructured states of high purity cobalt were achieved by high pressure torsion (HPT) at pressures of 4 and 8 GPa and temperatures of 300 and 77 K. Changes of crystallographic texture, grain sizes and phase transformations as a result of HPT and subsequent annealing have been measured and analyzed. Mechanical properties of nanostructured Co were studied by microhardness measurements at 300 K, and uniaxial compression at temperatures 300, 77 and 4.2 K. Comparison of the strength characteristics, plasticity and strain hardening of the nanostructured and coarse grained Co has been carried out. Micromechanisms of plastic deformation of Co during HPT deformation and uniaxial compression are discussed.

In this study, ARB process was used to produce Cu/Nano ZnO composite and samples were subjected up to six ARB cycles. Microstructural and mechanical properties of the composite within different ARB cycles were investigated by scanning electron microscopy (SEM) and tensile and micro hardness tests. The results showed that increasing the number of cycles, not only helped the distribution of reinforcing Nano-reinforcement in the matrix, but also improved the initial bonding strength, so that at final cycles, structural integration was achieved. Mechanical experiments also showed that increasing the number of ARB cycles, increased yield and ultimate strengths as well as micro hardness. However, elongation decreased up to second cycle and then increased by later final cycles. SEM studies of the fracture surfaces after the tensile test showed that the fracture mechanism of the composite was shear ductile rupture.

Mechanical properties of Ni-18.75 at.% Fe in coarse grained (average grain size 15 gm) and nanocrystalline (average grain size 22 nm) states were studied in uniaxial compression in the temperature range 4.2-350 K. Temperature dependences of the flow stress, strain rate sensitivity and activation volume of plastic deformation were measured. The thermal activation analysis of the experimental data has been fulfilled for the the plastic deformation value of 2 %. It was shown that plastic deformation in temperature range from 35 to 350 K in both studied structural states has the thermally activated type. Comparative analysis of low temperature thermal activation plastic deformation was carried out for the alloy in coarse grained and nanocrystalline states. Empirical estimates of parameters of the dislocation interaction with local barriers and internal stress value estimates were obtained for the both studied structural states. Analysis of the results indicates that different mechanisms control the thermal activation plasticity of the Ni-18.75 at.% Fe alloy in coarse grained and nanocrystalline states. Possible mechanisms, which control plactisity of the studied states, are disscussed.

Experiments were conducted on two different two-phase alloys, the Al-33% Cu eutectic and the Zn-22% Al eutectoid. These alloys were processed by high-pressure torsion (HPT) and then measurements were taken to determine the distributions of hardness values across the disk diameters and tensile tests were conducted to examine the potential for achieving superplastic elongations. Both alloys showed grain refinement through the HPT processing but the Al-Cu alloy exhibited a conventional work-hardening with torsional straining whereas the Zn-Al alloy exhibited a work-softening due to the loss of Zn-rich precipitates under the high imposed pressure. Excellent superplastic elongations were achieved in both alloys when pulled in tension at elevated temperatures with a maximum elongation of 1800% in the Zn-Al alloy.

High-pressure torsion (HPT) was conducted on disks of a Bi-Sn eutectic alloy under a pressure of 6.0 GPa. The microstructural evolution was studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Measurements of Vickers microhardness showed decreasing strength caused by strain weakening after HPT processing. Tensile testing was performed under initial strain rates from 10⁻⁴ to 10⁻² s⁻¹ at room temperature. The results demonstrate a much improved elongation to failure for the Bi-Sn alloy after HPT- processing. The Bi-Sn alloy processed through 10 turns gave an elongation to failure of more than 1200% at an initial strain rate of 10⁻⁴ s⁻¹ at room temperature which is significantly larger than the elongation to failure of ~110% in the as-cast Bi-Sn alloy under the same tensile conditions.

The severe plastic deformation (SPD) forming ultrafine-grained (nanocrystalline or nanosubgrained) structure is one of the most effective ways to improve the functional properties of Ti-Ni-based shape memory alloys [1, 2]. In the present work, the SPD of near-equiatomic Ti-Ni alloy was carried out using the multi-axial deformation module Max-strain, which is a part of the physical simulation system "Gleeble 3500". The deformation was performed at a constant temperature of 400°C with speed of 0.5 mm/s in six passes without interpass pauses. The accumulated true strain was about 3. As a result, a mixed ultrafine-grained/subgrained structure with grain/subgrain sizes from 50 to 300 nm and a high density of free dislocations formed. The resulting structure is close to a nanoscale region and provides a significant advantage in the basic functional property – completely recoverable strain – as compared with a conventional recrystallized structure: 7% versus 2%.

The strain-rate sensitivity of coarse-grained Ti-50.0at.%Ni alloy was studied in the 20 to 500°C temperature range and 10⁻³ to 10⁻⁵ s⁻¹ strain-rate range using the stain-rate jump test. The strain rate sensitivity at a strain rate as low as 10⁻⁶ s⁻¹ was determined using the creep test. A maximum strain-rate-sensitivity exponent m of 0.5 was measured at 500°C in the [10⁻⁵ -10⁻⁶]s⁻¹ strain-rate range.

The paper focuses on the study of the shape memory effect (SME) and two-way SME (TWSME) in nanostructured Ti-50.7 at.%Ni alloy. Two different types of structure were studied: nano-subgrained structure (annealing after the moderate deformation with true strain e = 0.6) and nanocrystalline structure (annealing after the severe plastic deformation with true strain e = 1.55). A homogenizing annealing at 700°C for 20 minutes served as a reference heat treatment (recrystallized structure of austenite). The SME training procedure was carried out in bending under load using eight various isothermal and non-isothermal modes covering all phase states and their combinations. The maximum recovery strain (ε_r = 14.7%) in Ti-50.7%Ni alloy is provided by the nano-subgrained structure with the grain size ≤ 5 pm obtained as a result of 10 h-aging after deformation with true strain e = 0.6, loading in the R-phase state with subsequent cooling in the loaded condition through R→B19' transformation under loading strain ε_t = 15,7 %. The maximum TWSME value ε_tw = 3.5% is provided by the loading in the R-phase state and further unloading.

Processing by Equal-Channel Angular Pressing (ECAP) is generally considered superior to most other SPD techniques because it uses relatively large bulk samples. However, due to their low deformability it has proven almost impossible to successfully process NiTi alloys by ECAP at room temperature and therefore the processing is conducted at elevated temperatures. Recently, a new billet design was introduced and it was used to achieve the successful processing of NiTi shape memory alloys by ECAP. In this procedure, a NiTi alloy was inserted as a core within an Fe sheath to give a core-sheath billet. In this research, a NiTi was processed by one pass ECAP with this new billet design at room temperature. The structural evolution during annealing was investigated by X-ray diffraction (XRD) and microhardness measurements. Post deformation annealing (PDA) was carried out at 400°C for 5 to 300 min and the results indicate that the shape memory effect improves by PDA after ECAP.

Mg matrix composites reinforced by natural bone constituent hydroxyapatite (HA) particles have shown promising in-vitro corrosion resistance but are inconsistent in both electrochemical and mechanical performances because of severe particle segregations. The present work was carried out to investigate the feasibility of a novel technology that combines high shear solidification and equal channel angular extrusion (ECAE) for fabricating Mg-HA nanocomposites. Experiments showed that the high shear solidification resulted in a fine and uniform grain structure with a globally uniform HA nanoparticles in fine clusters and the ECAE processing of the as-cast composites resulted in further grain refinement and more importantly the breakdown of nanoparticle aggregates, leading to the formation of a dispersion of true nanoparticles in the Mg alloy matrix with improved mechanical properties. This paper describes mainly the microstructural features and mechanical performance of Mg-3Zn-0.5Zr-xHA (x = 1, 3, 5, 10) nanocomposites, in which the HA was in spherical shape with an average diameter of ~20nm

This study is focused on the fatigue properties of the UFG Ti Grade 4 and its biocompatibility. The UFG titanium was produced by ECAP-Conform in combination with subsequent drawing, which allows fabricating rods of up to 3 mm suitable for industrial applications. The endurance limit of smooth and notched samples of UFG Ti is considerably higher than in conventional Ti. The UFG Ti also demonstrates an increased capacity of human osteoblast-like U2OS cells to colonize and, therefore, better osseointegration. Torsional strength of standard Ti-6Al-7Nb products and UFG Ti Grade 4 products was evaluated. An advantage of the UFG titanium over the conventional coarse-grained material was shown.

In this talk we show that cold rolling (CR) could be used to enhance hydrogen sorption properties of magnesium and magnesium alloys. In particular, cold rolling could reduce the first hydrogenation time, the so-called activation. Pure magnesium, commercial AZ91D alloy, and an experimental creep resistant magnesium alloy MRI153 in the as-cast and die-cast states were investigated. We found that both MRI and AZ91 alloys present faster activation kinetic than pure magnesium. This could be explained by the texture, higher number of defects, and nanostructure in CR materials but also precipitates at the grain boundaries. The effect of filing was also investigated.

Severe mechanical processing routes based on high-energy ball milling (HEBM) or severe plastic deformation (SPD) can be used to produce Mg nanomaterials for hydrogen storage applications. In the last few years, we have been exploring in our research group different SPD processing routes in Mg systems to achieve good activation (first hydrogenation) and fast H-absorption/desorption kinetics, combined with enhanced air resistance. In this paper, we compare SPD techniques applied to Mg with HEBM applied to MgH₂. Both advanced – melt spinning (MS), high-pressure torsion (HPT) – and more conventional – cold rolling (CR), cold forging (CF)- techniques are evaluated as means of production of bulk samples with very refined microstructures and controlled textures. In the best SPD processing conditions, attractive H-absorption/desorption kinetic properties are obtained, which are comparable to the ones of MgH₂ milled powders, even if the needed temperatures are higher – 350°C compared to 300°C.CR and CF stand out as the processes with higher potential for industrial application, considering the level of the attained hydrogen storage properties, its simplicity and low cost.

The effect of equal channel angular pressing in parallel channels (ECAP-PC) and subsequient artificial ageing on the microstructure and room temperature mechanical properties of the commercial aluminum alloys 6063 (Al-0.6Mg-0.5Si, wt.%) and 6010 (Al-0.8Mg-1.0Si-0.15Cu-0.25Mn, wt.%) was investigated. It was shown that mechanical strength of the ECAP-PC processed Al alloys is higher compared to that achieved in these alloys after conventional thermo-mechanical processing. Prior ECAP- PC solution treatment and post-ECAP-PC artificial aging can additionally increase the mechanical strength of both Al alloys. Under optimal artificial ageing conditions, the yield strength (YS) of 299 MPa and ultimate tensile strength (UTS) of 308 MPa was achieved in the 6063 alloy, whereas YS of 423 MPa and UTS of 436 MPa was achieved in the 6010 alloy.

In this study, Al-2%Fe samples extracted from a cast ingot in the shape of rings were processed by High-Pressure Torsion (HPT) at room temperature. Suitable specimens were extracted for evaluation of mechanical properties and electrical resistivity. High tensile strength of ~600 MPa was attained by HPT due to grain refinement down to an average grain size of ~130 nm and by subsequent aging accompanied by nano-sized (~10 nm) AhFe precipitates. The resulting conductivity (IACS%) was recovered from ~40% in the steady state after HPT to well above 50% in the peak-aged condition, which is in the range of current Al electrical alloys.

The influence of severe plastic deformation on strength and electrical conductivity in the Cu-Cr copper alloy has been studied. Microstructure of ultrafine-grained samples was investigated by transmission electron microscopy and X-ray diffraction with special attention on precipitation of small chromium particles after various thermal treatments. Effect of dynamic precipitation leading to enhancement of strength and electrical conductivity was observed. It is shown that ultrafine-grained samples enable to demonstrate the combination of enhanced thermal stability up to 500°C, high ultimate tensile strength of 790-840 MPa and enhanced electrical conductivity of 81-85% IACS. The contributions of grain boundaries and precipitates to enhanced properties of ultrafine-grained copper alloy are discussed.

CuCrZr alloys exhibit very good relation between mechanical properties and electrical conductivity. However, for its use in some advanced applications improvement of mechanical strength while preserving high electrical conducting is required. Therefore, in this work a CuCrZr alloy was subjected to a series of thermo-mechanical treatments, including solution annealing and water quenching, SPD processing (using hydrostatic extrusion and ECAP) as well as aging in order to improve mechanical strength. The influence of these processing procedures on microstructure features and mechanical properties was determined by TEM observation and microhardness measurements, respectively. Electrical conductivity of the samples was measured by four-points method. The results have shown that it is possible to improve mechanical strength while preserving good electrical conductivity by a proper combination of SPD processing and heat treatment.

The aim of this work was to produce a material with high strength and electrical conductivity. Two aluminium alloys: Al 6101 and 6201 were used for investigation. Improvement of mechanical properties was obtained by severe plastic deformation, using Hydrostatic Extrusion (HE). To examine mechanical properties of the materials microhardness and tensile tests were carried out. Furthermore, the microstructure analysis was carried out using TEM and light microscopy. Electrical conductivity of materials was measured by 4-wire method. It was found that in the material processed by HE tensile strength and microhardness increased about twice. The biggest strength of 356 MPa was obtained for alloy 6201 after HE. In this case the reduction of a diameters from 20 to 5 mm was used. Examination of the microstructure revealed that as a result of HE grain size refinement to 0.5 micrometer occurred. It was also found that the material has the electric conductivity of about 52% IACS.

The reduction of grain size down to several tens or hundreds of nanometers leads to the enhancement of radiation resistance of metals. Based on this approach, the aim of the Labex EMC3 (Energy Materials and Clean Combustion Center) project "Naninox" is (1) to study the stability of the microstructure of a nanostructured 316 stainless steel under ion irradiation and (2) to link between this microstructure and the properties (corrosion resistance and the microhardness) of the steel (thanks to a better irradiation resistance, a better corrosion resistance and higher mechanical properties after irradiation are expected in the ultra-fine grained stainless steel). Ultrafine grained 316L austenitic stainless steel samples have been produced by high pressure torsion (HPT) at 430°C and then ion irradiated in Jannus facilities (CEA Saclay) at 450°C and 5 displacements per atoms (dpa). Their microstructure is characterized before and after irradiation by atom probe tomography, X-ray diffraction and transmission electron microscopy. Corrosion behavior in NaCl solution is tested and nano-indentation tests are performed. The first results obtained by atom probe tomography described in this paper indicate that the microstructure of ultrafine grain 316 austenitic stainless steel is more stable under irradiation than the microstructure of a coarse grain 316 austenitic stainless steel.

The effect of deformation routes on the microstructure, mechanical, and electrochemical properties of low CN Fe-20%Cr alloys by equal channel angular pressing (ECAP) has been investigated in detail focusing on the anisotropy of the microstructure. This alloy is pressed at 423K up to eight passes via the so-called routes A, Bc and C. The continuous refinement of the microstructure is sustained by ECAP until the sub-grain range. However, the degree of anisotropy of microstructural development was different among the three deformation routes. Materials processed by Route Bc exhibited a comparable micro-hardness value in three orthogonal planes than those processed by routes A and C. Pitting corrosion characteristics of the ECAP processed sample were investigated using an electrochemical potentiodynamic test. The increased pitting potential along with an increased number passes of ECAP were explained by enhanced protective passive layer of ultrafine grain structure, as compared to the coarse grain counterpart.

The effect of strain rate on strength, ductility and uniformity of deformation of ultrafine-grained aluminum processed by equal channel angular pressing through plastic flow at room temperature in a strain rate interval of 1.0×10⁻⁵ to 8.6×10⁻³ s⁻¹ have been studied. The contribution of grain boundary sliding to the overall deformation (η) was calculated using displacement of grains relative to each other in local areas of a gage length. The strength characteristics and tendency toward necking diminish when decreasing the strain rate, while elongation up to failure and η increase. Improving the ductility at low strain rates should be related to the increase in strain rate sensitivity caused by enhancing η, reaching 45% in the local areas of the neck and totaling 72% in the local areas of uniformly elongated portion. The relatively low value of the strain rate sensitivity (m=0.08) is probably due to the heterogeneity of grain structure in UFG aluminum.

Nanocrystalline materials are well known to have enhanced diffusion properties, especially due to their high grain boundary density which are fast diffusion channels in the material. In this paper, a highly pure iron sample is treated by Nano Peening^® to obtain a nanostructured layer with nanometric grains in the top surface. Then, the grain size distribution is measured by EBSD and optical micrography to fit with an analytical law. It is shown that an exponential law is a good estimator for the grain size distribution after Nano Peening^®. Then, using this grain size distribution, the diffusivity distribution is calculated with an analytical model we recently proposed. A 1D finite element simulation of nitrogen diffusion is then performed with this distribution and the concentration profiles are compared with those extracted from a simulation with a constant grain size distribution. Simulations show that Nano Peening^® significantly enhances diffusion, dividing the nitriding duration by 2 or by obtaining a 120% gain in the nitriding depth.

Ultrafine-grained interstitial-free steel fabricated by the accumulative roll-bonding method was subjected to tensile tests and analyses of AFM, TEM and XRD to identify the effects of interaction between dislocations and grain boundaries (GB) on the deformation mechanism. The AFM analyses indicated that the main deformation mechanism of this material changed from dislocation motion to grain boundary sliding (GBS) with decreasing strain rate. TEM observations and XRD analysis revealed showed that dislocations piled up at GB and the dislocation density decreased with increasing strain. Those suggest the dislocations are absorbed into GB during deformation, activating slip-induced GBS.

The Zn-22% Al eutectoid alloy and the Pb-62% Sn eutectic alloy were processed by high-pressure torsion (HPT) over a range of experimental conditions. Both alloys exhibit similar characteristics with significant grain refinement after processing by HPT but with a reduction in the hardness values by comparison with the initial unprocessed conditions. After storage at room temperature for a period of time, it is shown that the microhardness of both alloys gradually recovers to close to the initial unprocessed values. Electron backscatter diffraction (EBSD) measurements on the Pb-Sn alloy suggest that the self-recovery behaviour is correlated with the fraction of high-angle grain boundaries (HAGBs) after HPT processing. Thus, high fractions of HAGBs occur immediately after processing and this favours grain boundary migration and sliding which is important in the self-annealing and recovery process. Conversely, the relatively lower fractions of HAGBs occurring after annealing at room temperature are not so conducive to easy migration and sliding.

An UFG austenitic stainless steel of type 316 was produced by high pressure torsion at two different temperatures. As a result different nanostructures were observed in the investigated alloy characterized by different grain size and dislocation density. It was reported that the steel processed at both temperatures was characterized by significantly enhanced strength, which, in case of the steel processed at 430°C, exceeds the value expected for the given grain size according to Hall-Petch relation. This extra-strength is supposed to be due to the observed nanostructural features as segregations/clusters of solutes in grain boundary area formed by severe plastic deformation.

Contributions of different strengthening mechanisms to yield strength of carbon steels C 10 (0.1 % C) and C 45 (0.45 % C) with ultrafine-grained microstructures have been analyzed in this work based on the precision investigation of the microstructure by electron microscopy, 3D atom probe tomography, and mechanical properties. Estimated values of yield stress showed satisfactory agreement with the experimental results. It is shown that significant contribution to strengthening is made by carbides. In particular, as the carbon content increases in carbon steels, the volume fraction of cementite increases and, accordingly, there is a bigger deviation of the yield strength value from the classical Hall-Petch relationship. The relative contribution of grain boundary strengthening into the yield stress is reduced due to an increased proportion of precipitate strengthening.

An extension of the classical continuum mechanics model is provided for the solution of boundary value problems at the nanoscale. The resulting continuum nano-mechanical model is based on the introduction of new terms to account for the interaction of bulk and surface points of the medium, which becomes significant as the specimen size is reduced down to the nanometer level. The model can be used to interpret deformation and diffusion phenomena in nanocrystalline (NC) and ultrafine grain (UFG) polycrystals, where a large number of internal surfaces (e.g. grain/twin boundaries) are present. When small material volumes are considered, random effects of the underlying microstructure become pronounced and their interpretation cannot be addressed with deterministic models alone. In this case, the continuum nanomechanics model may be enhanced with stochastic terms accounting for their competition with their deterministic gradient counterparts. The resulting combined gradient-stochastic model can be used to interpret intermittent plasticity and size-dependent serrated stress-strain curves in micro/nano pillars. These ideas have been applied to address certain benchmark problems and configurations of nanoelasticity, nanodiffusion and nanoplasticity. Non-singular expressions can be derived for stresses and strains in the neighborhood of dislocation lines and crack tips contained in a nanograin. Non-linear concentration depth profiles for diffusion in NCs are obtained in agreement with experiments. Corresponding results are obtained herein for coupled elasto-diffusion processes and related size-dependent phase transformation diagrams. When differential equations are not available, deformation features may be revealed through a statistical analysis of the relevant experimental data. This is done here for the interpretation of statistical features of deformed UFG alloys exhibiting serrated stress-strain curves and fractal shear bands.

Looking at severe plastic deformation experiments, it seems that crystalline materials at yield behave as a special kind of anisotropic, highly viscous fluids flowing through an adjustable crystal lattice space. High viscosity provides a possibility to describe the flow as a quasi-static process, where inertial and other body forces can be neglected. The flow through the lattice space is restricted to preferred crystallographic planes and directions causing anisotropy. In the deformation process the lattice is strained and rotated. The proposed model is based on the rate form of the decomposition rule: the velocity gradient consists of the lattice velocity gradient and the sum of the velocity gradients corresponding to the slip rates of individual slip systems. The proposed crystal plasticity model allowing for large deformations is treated as the flow-adjusted boundary value problem. As a test example we analyze a plastic flow of an single crystal compressed in a channel die. We propose three step algorithm of finite element discretization for a numerical solution in the Arbitrary Lagrangian Eulerian (ALE) configuration.

In this paper the focus is laid on the thermal stability of nanocrystalline materials obtained by severe plastic deformation. TEM investigations show that rotational defects act as stabilising elements in grains as well as at grain boundaries.

A classic explanation for the Hall-Petch relationship is given by the stress field of a single dislocation pile-up perpendicular to the grain boundary. Similarly, the gradual compensation of the stress fields of pile-ups on both sides of the boundary has been invoked to explain the transitory effects observed in the stress- strain curves of ultrafine grained polycrystals. This paper studies the effects of introducing deviations of the highly simplified geometry mentioned above, using the proper mathematical approximations of linear elastic dislocation theory. Multiple pile-ups invalidate the conclusions drawn from the single pile-up model. Pile-ups in multiple grains are assessed by a highly idealised model of an infinite array of periodical pile-ups. In the latter case, screening is always perfect. By considering the Peach-Köhler force between dislocations mutually disoriented grains, the magnitude of the fluctuations around such ideal case can be estimated. However, using sound probabilistic arguments to calculate the free path for dislocation slip in fine-grained polycrystals, it is found that the amount of dislocations that can be stored in the pile- ups is generally too small to explain the strong grain size effects observed experimentally.

The ultrafine-grained structures produced by cold (20 °C) and warm (450 °C) high- pressure torsion in low-carbon steel were studied using transmission electron microscopy and X-ray analysis. After cold high-pressure torsion, the size of fragments is smaller (100 nm) and structure is more homogeneous in comparison with warm deformation (120 nm). As a result of high-pressure torsion, the microhardness of steel investigated has been increased up to 600 HV and 570 HV after cold and warm deformation respectively.

The existence of basal-prismatic interfaces and their roles in twinning of hexagonal materials have recently attracted appreciable attention of scientific community. In this paper, we utilize molecular statics to investigate the formation of basal-prismatic facets in the twin boundary of magnesium. This interface is shown to be the consequence of a collective motion and interaction of twinning disconnections. By analyzing volume deformations caused by the migration of a single basal-prismatic interface, we show that the passage of this interface distorts the material equivalently to twinning shear.

A combination of rotary swaging and optimized precipitation hardening was applied to generate ultra fine grained (UFG) microstructures in low alloyed high performance Cu-based alloy CuNi3Si1Mg. As a result, ultrafine grained (UFG) microstructures with nanoscopically small Ni₂Si-precipitates exhibiting high strength, ductility and electrical conductivity can be obtained. Grain boundary pinning by nano-precipitates enhances the thermal stability. Electron channeling contrast imaging (ECCI) and especially electron backscattering diffraction (EBSD) are predestined to characterize the evolving microstructures due to excellent resolution and vast crystallographic information. The following study summarizes the microstructure after different processing steps and points out the consequences for the most important mechanical and physical properties such as strength, ductility and conductivity.

The effect of equal channel angular pressing on the microstructure of copper samples was studied by X-ray line profile analysis. Pure Cu samples were processed by equal channel angular pressing with 3 passes in route A. Samples were taken from the vicinity of the channel intersection, and along a profile across the deformation zone, microhardness and XRD measurements were performed. For the high resolution line profile analysis of the diffraction spectra, convolutional-multiple-whole-profile CMWP method was applied, dislocation density and grain size were calculated, furthermore the density of twin boundaries were determined. Results show a rearrangement in the dislocations in the third pass leading to a rise in the density of twin boundaries.

The ultrafine-grained microstructure of pure copper processed by equal-channel angular pressing and its temperature-induced changes were evaluated in order to characterize heterogeneous distribution of fine- and larger-sized grains in the microstructure. ECAP was conducted at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The subsequent extrusion passes were performed by route Bc up to 8 ECAP passes and tested under constant load. Creep test was performed on the samples processed by 8 ECAP passes in tension at 373 K under an applied stress 260 MPa. The analyses of microstructure were performed by 3 dimensional electron-back scatter diffraction (3D EBSD) technique. The volume characteristics of microstructure and its inhomogeneity were evaluated and the relationships microstructure/creep behaviour of UFG copper was discussed.

Accumulative roll bonding (ARB) was applied to three FCC metals, such as Al, Cu and Ni. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were made to evaluate dislocation density ρ of the ARB processed FCC metals. The values of ρ of ARB processed Cu and Ni increased rapidly after the first ARB cycle, and then, tend to saturate after the following cycles. The evaluated values of ρ of both ARB 8-cycled Cu and Ni using DSC were around 2×10¹⁵ m⁻². Whereas, those using XRD were around 5×10¹⁴m⁻² (for Cu) and 3×10¹⁴m⁻² (for Ni). Although the ρ values depend on the measurement methods, the trends that DSC values are about an order of magnitude higher than XRD values seem to be common. In the case of Al, dislocation density evaluated using XRD increased to about 1×10¹³m⁻² at the first ARB cycle, and then gradually decreased to about 1×10¹²m⁻² with increasing number of ARB cycles.

Magnesium alloys are characterised by their low density, high specific strength and stiffness. But, the potential application of Mg is limited by its low room-temperature ductility & formability. Formability can be improved by developing an ultrafine grained (UFG) structure. Equal channel angular pressing (ECAP) is a well known process that can be used to develop an ultrafine grained microstructure. The aim of this study was to investigate the flow behaviour of AZ31B magnesium alloy after ECAP. The specimen was subjected to three passes of ECAP with a die angle of 120° using processing route Bc. The processing temperature was 523 K for the first pass and 423 K for the subsequent two passes. The microstructure characterisation was done. Compression tests of ECAPed and annealed specimens were carried out at strain rates of 0.01 – 1s⁻¹ and deformation temperatures of 200 – 300°C using computer servo-controlled Gleeble-3800 system. The value of activation energy Q and the empirical materials constants of A and n were determined. The equations relating flow stress and Zener-Hollomon parameter were proposed. In the case annealed AZ31, the activation energy was determined to be 154 kJ/mol, which was slightly higher than the activation energy of 144 kJ/mol for ECAPed AZ31.

In the present study the possibilities of grain refinement was investigated by applying large-scale of cyclic plastic deformation to aluminum at ambient temperature. The specimens are processed by multiaxial forging, which is one of the severe plastic deformation techniques. The aim of the experiments with the aluminum alloy 6082M was the determination of the equivalent stress and strain by multiaxial forging and the investigation of evolution of mechanical properties in relation with the accumulated deformation in the specimen. The mechanical properties of raw material was determined by plane strain compression test as well as by hardness measurements. The forming experiments were carried out on Gleeble 3800 physical simulator with MaxStrain System. The mechanical properties of the forged specimens were investigated by micro hardness measurements and tensile tests. A mechanical model, based on the principle of virtual velocities was developed to calculate the flow curves using the measured dimensional changes of the specimen and the measured force. With respect to the evolution of these curves, the cyclic growth of the flow stress can be observed at every characteristic points of the calculated flow curves. In accordance with this tendency, the evolution of the hardness along the middle cross section of the deformed volume has also a nonmonotonous characteristic and the magnitudes of these values are much smaller than by the specimen after plane strain compression test. This difference between the flow stresses respect to the monotonic and non-monotonic deformation can be also observed. The formed microstructure, after a 10-passes multiaxial forging process, consists of mainly equiaxial grains in the submicron grain scale.

This work describes the effect of equal channel angular pressing (ECAP) on the microstructure and creep properties of pure copper and its two binary alloys with addition of small amounts of Zr or Co. The ECAP pressing was performed at room temperature by route Bc up to 12 passes using a die with an internal angle of 90° between the two parts of the channel. Ultrafine-grained (UFG) microstructure formed through ECAP process has been studied by methods of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with the electron backscatter diffraction (EBSD) unit. Tensile creep tests were conducted in tension at temperature 673 K and at different applied stresses on ECAP material and, for comparison purposes, on unpressed coarse-grained states of materials under investigation too. It was found that both alloys processed by ECAP exhibited similar character of creep behaviour. Creep resistance was markedly improved after first two ECAP passes in comparison with creep behaviour of unpressed materials. The minimum creep rate of ECAP material may be up to two orders of magnitude lower than that of unpressed material. However, subsequent ECAP passes lead to a decline of creep life and the difference in the minimum creep rate for the ECAP material and unpressed state consistently decreases with increasing number of ECAP passes. Further, ECAP process led to significant improvements in fracture strain. The link between microstructural processes and creep behaviour of pressed copper and its selected alloys is examined in detail.

In this paper the influence of high pressure torsion (HPT) on the structure of Mg-Zn- Ca alloy is studied. The microstructure before and after HPT and after additional annealing has been studied by the scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results of microhardness measurements and tensile tests of HPT samples are discussed.

The strain hardening behavior of an ARMCO iron processed by ECAP at room temperature up to sixteen passes following route Bc was investigated through Hollomon and differential Crussard-Jaoul models. Results indicate that the Hollomon analysis shows some deviations from the experimentally determined true stress – true strain curves while the differential Crussard-Jaoul analysis based on the Ludwik equation and the modified Crussard- Jaoul analysis based on the Swift equation fit better when two work hardening exponents are considered. As expected, the strength of the material increased with the number of ECAP passes. Indeed the ultimate tensile stress reached a maximum of ~900MPa after 16 passes, which is more than three times higher than the UTS of the annealed material. Nevertheless, the strain hardening capacity of the material was reduced in comparison with the material without severe plastic deformation. For that reason the tensile ductility was also reduced at increasing ECAP passes. The increase in strength was attributed to the reduction of the grain size through refined sub-grains with high density of dislocations. After sixteenth passes the original grain size (namely 70 mm) was reduced down to 300 to 400 nm observing a good correspondence with the Hall-Petch relationship. The microstructural analysis, carried out by EBSD, showed an increasing amount in the fraction of high Angle Grain Boundaries (HAGB) after 1 pass due to the regeneration of the microstructure with a smaller grain size.

Dynamic tensile extrusion (DTE) tests with the strain rate order of ~10⁵ s⁻¹ were conducted on coarse grained (CG) Cu and ultrafine grained (UFG) Cu. ECAP of 16 passes with route Bc was employed to fabricate UFG Cu. DTE tests were carried out by launching the sphere samples to the conical extrusion die at a speed of ~475 m/sec in a vacuumed gas gun system. UFG Cu was fragmented into 3 pieces and showed a DTE elongation of ~340%. CG Cu exhibited a larger DTE elongation of ~490% with fragmentation of 4 pieces. During DTE tests, dynamic recrystallization occurred in UFG Cu, but not in CG Cu. In order to examine the DTE behavior of CG Cu and UFG Cu under very high strain rates, a numerical analysis was undertaken by using a commercial finite element code (LS-DYNA 2D axis-symmetric model) with the Johnson – Cook model. The numerical analysis correctly predicted fragmentation and DTE elongation of CG Cu. But, the experimental DTE elongation of UFG Cu was much smaller than that predicted by the numerical analysis. This difference is discussed in terms of microstructural evolution of UFG Cu during DTE tests.

Crystal lattice rotations induced by shear bands developed in an AA1050 aluminium alloy have been examined in order to investigate the influence of the finegrained structure on the slip propagation across the grain boundaries and the resulting texture evolution. Samples of the AA1050 alloy were pre-deformed in ECAP up to 6 passes via route C, then machined and further compressed in a channel-die up to ~25% at room temperature. The microstructure and texture were characterized by SEM equipped with a high resolution EBSD facility.

The ECAP-processing leads to the formation of a fine grained structure. The grains were grouped into nearly complementarily oriented layers. During the secondary straining in the channel-die, the layers of fine grains, initially situated almost parallel to the compression plane, undergo deflection within some narrow areas. This is the beginning stage of the macroscopic shear band (MSB) formation. In all the deformed grains examined (within MSB) a strong tendency for strain-induced re-orientation could be observed. The SEM orientation mapping shows how the layers of flattened grains are incorporated into the MSB area, and what kinds of mechanisms are responsible for the strain accommodation at the macro-scale. Finally, a crystallographic description of the mechanism of MSB formation in AA1050 aluminium alloy is proposed based on the local lattice re-orientations due to localized kinking.

This paper presents experimental results on the thermodynamics of deformation process and mechanical behavior of the ultrafine grained aluminum alloys under dynamic compression. Dynamic compression tests were performed on a Hopkinson-Kolsky split bar at the strain rate of 103 s'1 with simultaneously recording the surface temperature of samples by an infrared camera. Energy dissipation ability was determined for ultrafine-grained alloys. An inverse strain rate dependency of dynamic yield strength was observed in the ultrafine-grained Al-Zn-Mg-Cu alloy (A7075).

Rods of grade 2 Ti were processed by Equal-Channel Angular Pressing (ECAP) (ϕ = 120° at 573 K) employing 2, 4 and 6 passes. The same billets were further deformed by High- Pressure Torsion (HPT) at room temperature, varying both the hydrostatic pressure (1 and 6 GPa) and the number of rotations (n = 1 and 5). The ECAP and HPT samples were studied by synchrotron radiation at DESY-Petra III GEMS line. On the ECAP samples, textures were thus determined while for both ECAP and HPT samples the measurements were further analyzed by MAUD. Domain sizes and phase volume fractions were determined as a function of the radial direction of the samples. Alpha and Omega phases were detected in different amounts depending mostly on hydrostatic pressure and shear deformation. These transition phases can be pressure-induced during HPT processing and the results of Vickers microhardness measurements were related to the processing parameters and to the amounts of these phases.

The onset of Severe Plastic Deformation (SPD) regime is quite instructive on the possible origins of the nano-microstructures developed in metals and alloys. It is known that grain fragmentation and dislocation accumulation, among other defects, proceed at different paces depending fundamentally on grain orientations and active deformation mechanisms. There have been many attempts to characterize nano-microstructure anisotropy, leading all of them to sometimes contradictory conclusions. Moreover, the characterizations rely on different measurements techniques and pos-processing approaches, which can be observing different manifestations of the same phenomena.

On the current presentation we show a few experimental and computer pos-processing and simulation approaches, applied to some SPD/alloy systems. Williamson-Hall and Convolutional Multiple Whole Profile (CMWP) techniques will be applied to peak broadening analysis on experimental results stemming from laboratory Cu Ka X-rays, and synchrotron radiation from LNLS (Laboratório Nacional de Luz Síncrotron, Campinas, Brazil) and Petra III line (HEMS station, at DESY, Hamburg, Germany).

Taking advantage of the EBSD capability of giving information on orientational and topological characteristics of grain boundaries, microstructures, grain sizes, etc., we also performed investigations on dislocation density and Geometrically Necessary Dislocation Boundaries (GNDB) and their correlation with texture components.

Orientation dependent nano-microstructures and domain sizes are shown on the scheme of generalized pole figures and discussions provide some hints on nano-microstructure anisotropy.

Different severe plastic deformation comprise equal channel angular pressing (ECAP), shaped cold rolling and drawing, or combined were applied on pure iron to obtain nano structured grains. The results show the formation of high concentration of excess free volume up to about 4% in the cold rolled and drawn specimens. Emphasis has been placed on atomic force microscopy (AFM) observations as additional characterization tools that complement the information provided by other techniques. Since the surface of the materials can be observed with atomic-scale resolution, the AFM is a powerful technique to study porous materials. The microscopy observations detect voids in the nanocrystalline Fe sample- processed by shaped rolling followed by drawing with applied true strain of 7- from nano to sub-micrometer in size. It seems that the coalescence of nanovoids could lead to the formation of micro-voids in the structure of deformed samples.

An AZ31 sheet was rolled in symmetrical and asymmetrical conditions to a total reduction of 50%. Twins and double twins are the dominant structural features observed after deformation. They were analyzed systematically with the help of a dedicated TEM attachment that provides orientation maps at nanoscale. This particular characterization technic is similar to SEM-EBSD tools but far less sensitive to strains. Twinning is shown to differ substantially with the introduction of a shear component. Despite their frequency, it is argued that twins have little effect on the forming process.

The present study investigates the texture features occurred during recrystallization of a Ti-29Nb-9Ta-10Zr-0.2O (wt.%) alloy processed by multi-pass cold-rolling, up to 90% thickness reduction. Data concerning alloy component phases and the lattice parameters of identified phases were obtained and analysed for all thermo-mechanical processing stages. Crystallographic texture changes occurred during alloy thermo-mechanical processing (coldrolling and recrystallization), were investigated using X-ray diffraction; by acquiring the pole figures data of the main β-Ti phase. Data concerning observed texture components and texture fibers was analysed using ϕ1 – Φ – ϕ2 Bunge system in ϕ2 = 0° and 45° sections. The γ textural fiber was analysed for all thermo-mechanical processing stages.

Equal Channel Angular Pressing (ECAP) can be used to control deformation and annealing textures. The initial texture has a significant role on texture development and intensity after deformation and anneal. In this work AA 1050 Al samples with different initial textures and initial strain of 0.3 were deformed in a I20° ECAP die. Deformation followed route A, yielding equivalents strains of 1 and 3 above the initial. After ECAP one of the samples was rolled to a thickness reduction of 70%. Texture evaluation was performed by x-ray analysis in the as deformed state and after annealing at 350°C for 1 h, by calculating orientation distribution functions. The microstructure was observed by optical and scanning electron microscopy.

Large billets (5 x 5 x 30) cm³ of technically pure aluminum (AA 1050) taken from thick rolled sheets were deformed at room temperature by single pass equal-channel angular pressing (ECAP). ECAP was done at different back pressures (0 – 60 MPa) using a square die with channels intersecting at 90° in sharp corners. The normal direction of rolling was taken parallel to the transverse direction of ECAP. The flow pattern was visualized by marker lines on split billets. The initial texture of the coarse-grained rolled sheet was measured by neutron diffraction. After ECAP, X-ray diffraction was used to measure the texture gradient from top to bottom of the billets. The results show, that with increasing back pressure the corner gap is closed and the flow line pattern becomes more symmetric. The flow line exponent increases strongly from top to bottom of the billets. Moreover, the inhomogeneous deformed zone at the bottom of the billets becomes smaller. The texture changes from a typical rolling texture to a typical shear texture with the intensity of the different shear texture components changing with back pressure. For the ACcomponent splitting is observed. The texture changes are discussed considering Toth's flow line model and grain refinement.

NiAl is an intermetallic compound with a brittle-to-ductile transition temperature at about 300°C and ambient pressure. At standard conditions, it is very difficult to deform, but fracture stress and fracture strain are increased under high hydrostatic pressure. On account of this, deformation at low temperatures is only possible at high hydrostatic pressure, as for instance used in high pressure torsion. In order to study the influence of temperature on texture evolution, small discs of polycrystalline NiAl were deformed by high pressure torsion at temperatures ranging from room temperature to 500°C. At room temperature, a typical shear texture of body centred cubic metals is found, while at 500°C a strong oblique cube component dominates. These textures can be well simulated with the viscoplastic self-consistent polycrystal deformation model using the primary and secondary slip systems activated at low and high temperatures. The oblique cube component is a dynamic recrystallization component.

The production of Mg alloy AZ31B sheet in a single deformation step by large- strain extrusion machining (LSEM) is detailed. LSEM imposes intense simple shear in a narrow zone by constrained chip formation. The confined deformation and the associated in situ adiabatic heating are found to be the key factors in production of the Mg sheet without need for external (pre-) heating. A range of shear textures with basal planes inclined to the sheet surface are achieved by this processing. The basal plane inclination could be varied by controlling the strain path. Microstructures, both ultrafine-grained (100-500 nm) and conventional fine-grained (2-5 μm), have been obtained by controlling the adiabatic heating and the extent of dynamic recrystallization. The LSEM sheet with shear texture and fine grain size shows superior combinations of formability and strength compared to rolled sheet.

The development of nanocrystalline structures in austenitic stainless steels during large strain cold rolling and their tensile behavior were studied. The cold rolling to total equivalent strains above 2 was accompanied by the evolution of nanocrystalline structures with the transverse grain size of about 100 nm. The development of deformation twinning and martensitic transformation during cold working promoted the fast kinetics of structural changes. The development of nanocrystalline structures resulted in significant strengthening. More than fourfold increase in the yield strength was achieved. The strengthening of nanocrystalline steels after severe plastic deformation was considered as a concurrent operation of two strengthening mechanisms, which were attributed to grain size and internal stress. The contribution of internal stresses to the yield strength is comparable with that from grain size strengthening.

In the present work the influence of cryo-rolling to a true strain ε=2.66 on twinning and formation of ultrafine-grained/nanostructure in commercial-purity titanium and Fe-0.3C- 23Mn-1.5Al TWIP steel was quantified using scanning and transmission electron microscopy. Different influence of twinning on the kinetics of microstructure refinement and nanostructure formation in titanium and steel was revealed. In titanium twin boundaries during deformation transform into arbitrary high-angle grain boundaries thereby promoting the microstructure refinement to a grain/subgrain size of 80 nm. In steel twinning has less pronounced influence on the microstructure refinement. However, very fine grains/subgrains with the size of 30-50 nm was observed in the microstructure after rolling at 77K to a true thickness strain of 2.66.

The near threshold fatigue crack growth in ultrafine-grained (UFG) copper at room temperature was studied in comparison to conventional coarse-grained (CG) copper. The fatigue crack growth rates da/dN in UFG copper were enhanced at ΔK ≤ 7 MPa√m compared to the CG material. The crack closure shielding, as evaluated using the compliance variation technique, was shown to explain these differences. The effective stress intensity factor amplitude AKeff appears to be the same driving force in both materials. Tests performed in high vacuum on UFG copper demonstrate the existence of a huge effect of environment with growth rates higher of about two orders of magnitude in air compared to high vacuum. This environmental effect on the crack path and the related microstructure is discussed on the basis of fractography observations performed using scanning electron microscope and completed with field emission scanning electron microscope combined with the focused ion beam technique.

Mechanism of fatigue crack initiation was investigated in ultrafine-grained (UFG) magnesium alloy AZ91 processed by equal channel angular pressing (ECAP). Fatigue behaviour of UFG material was compared to the behaviour of material in an initial as-cast state. Focused ion beam technique (FIB) was applied to reveal the surface relief and early fatigue cracks.

Two substantially different mechanisms of crack initiation were observed in UFG structure, which can be characterized as bimodal even after 6 ECAP passes by route Bc. The bimodality consists in a coexistence of very fine grained areas with higher content of Mg₁₇Al₁₂ particles and areas exhibiting somewhat larger grains and lower density of particles. The fatigue cracks which initiate in areas of larger grains are related to the cyclic slip bands; this initiation mechanism is similar to that observed in cast alloy. The second initiation mechanism is related to the grain boundary cracking which takes place predominantly in the fine grained areas.

Low-cycle fatigue properties were investigated on Fe-20%Cr ferritic stainless steel processed by equal channel angular pressing (ECAP). The Fe-20%Cr alloy bullets were processed for one to four passes via Route-Bc. The ECAPed samples were cyclically deformed at the constant plastic strain amplitude ε_pl of 5x10⁻⁴ at room temperature in air. After the 1-pass ECAP, low-angle grain boundaries were dominantly formed. During the low-cycle fatigue test, the 1-pass sample revealed the rapid softening which continued until fatigue fracture. Fatigue life of the 1-pass sample was shorter than that of a coarse-grained sample. After the 4-pass ECAP, the average grain size reduced down to about 1.5 μm. At initial stage of the low-cycle fatigue tests, the stress amplitude increased with increasing ECAP passes. At the samples processed for more than 2 passes, the cyclic softening was relatively moderate. It was found that fatigue life of the ECAPed Fe-20%Cr alloy excepting the 1-pass sample was improved as compared to the coarse-grained sample, even under the strain controlled fatigue condition.

Samples of grade 2 Ti were processed by Equal Channel Angular Pressing (ECAP), either isolated or followed by further deformation by rolling at room temperature and at 170 K. The main interest of the present work was the evaluation of the effect of cryogenic rolling on tensile strength, fatigue limit and Charpy impact absorbed energy. Results show a progressive improvement of strength and endurance limit in the following order: ECAP; ECAP followed by room temperature rolling and ECAP followed by cryogenic rolling. From the examination of the fatigued samples a ductile fracture mode was inferred in all cases; also, the sample processed by cryogenic rolling showed very small and shallow dimples and a small fracture zone, confirming the agency of strength on the fatigue behaviour. The Charpy impact energy followed a similar pattern, with the exception that ECAP produced only a small improvement over the coarse-grained material. Motives for the efficiency of cryogenic deformation by rolling are the reduced grain size and the association of strength and ductility. The production of favourable deformation textures must also be considered.

Ultrafine-grained (UFG) Ti alloys have potential applications in osteosynthesis and orthopedics due to high bio-compatibility and increased weight-to- strength ratio. In current study, Ti6Al7Nb ELI alloy is processed through equal channel angular pressing-conform (ECAP-Conform) and subsequent thermomechanical processing to generate a UFG microstructure. The fatigue properties of UFG alloys are compared to coarse grained (CG) alloys. Our study demonstrates that the UFG alloys with an average grain size of ~180 nm showed 35% enhancement of fatigue endurance limit as compared to coarse-grained alloys. On the fracture surfaces of the UFG and CG samples fatigue striations and dimpled relief were observed. However, the fracture surface of the UFG sample looks smoother; fewer amounts of secondary micro-cracks and more ductile rupture were also observed, which testifies to the good crack resistance in the UFG alloy after high-cyclic fatigue tests.

The endurance limit of materials has been observed to be significantly increased in materials with an ultrafine grained microstructure [1, 2]. As this effect, however, has not yet been investigated in steels, fatigue experiments of an unalloyed medium carbon steel with a carbon content of 0.45 wt.-%, which was treated by high pressure torsion (HPT) [3-5] at elevated temperature were carried out. The treatments were applied to discs which had different initial carbide morphologies and showed an increase of hardness after HPT by a factor of 1.75 – 3.2 compared to the initial states, whereby the amount of increase depends on the initial carbide morphology. The maximum hardness achieved was 810 HV. The discs were cut into fatigue specimens in the form of bars of the size of 4 mm x 1 mm x 600 gm. Until a hardness of 500 HV the endurance limits correspond linearly with the hardness. This is no longer the case at higher hardness values, where inherent and process-initiated flaws lead to lower fatigue limits. The maximum endurance limit exceeded 1050 MPa in 4-point-micro-bending and at a load ratio of R = 0.1. Fractography revealed different crack initiation sites like pre cracks and shear bands [6, 7] resulting from HPT or fisheye fractures initiated from non-metallic inclusions.

Effect of initial grain size on fatigue behavior of an Al-6%Mg-0.35%Mn-0.2%Sc- 0.08%Zr-0.07%Cr alloy was examined. The initial CG microstructure with an average grain size of ~ 22 μm was manufactured by casting followed by solution treatment at 360 °C for 12 h. To produce the UFG condition, the alloy was subjected to equal-channel angular pressing (ECAP) at 320 °C up to a total strain of ~ 14. Extensive grain refinement provided the formation of fully recrystallized structure with an average grain size of 700 nm. It was shown that the formation of UFG structure provided +60% increases in yield stress and +25% increases in fatigue strength. Fundamentals of this effect of microstructure on the static strength, fatigue resistance and fracture modes are discussed.

Structural and devitrification behaviors of selected Mg-based amorphous alloys have been investigated for the Mg-Cu-Gd amorphous ribbon fabricated by repeated forced cold rolling. When amorphous ribbons were cold- rolled up to a thickness ratio of ~ 50%, the heat of crystallization (AHx) exhibited a reduction. In order to identify devitrification manner of the amorphous alloys, in-situ TEM (Transmission Electron Microscope) observations up to 623 K have been carried out for the as-fabricated ribbon and cold-rolled ribbon at 10 K temperature interval from 423 K. The nano-crystallization behaviors and mechanism of Mg-Cu-Gd alloy ribbon are discussed in terms of TEM observations and kinetic analysis.

Peculiarities of structure and mechanical behaviour of amorphous Ti₅₀Ni₂₅Cu₂₅ alloy were the focus of this research. Amorphous melt-spun ribbons and bulk crystalline samples were subjected to high pressure torsion (HPT) in order to modify their structure and mechanical behaviour. Some properties of obtained SPD-processed samples were compared with initial state with the help of x-ray diffraction (XRD), differential scanning calorimetry (DSC) and nanohardness tests. It was shown that according to XRD no nanocrystallization occurs during HPT of melt-spun ribbons yet at the same time high density of shear bands might be formed in the alloy. Due to the formation of shear bands with the excess free volume the decrease of hardness and crystallization temperature were observed in the alloy. Analysis of structural data and mechanical behaviour allowed us to assume, that SPD processing of melt- spun Ti₅₀Ni₂₅Cu₂₅ alloy might lead to the formation of structural state similar to the new kind of noncrystalline state – "nanoglass" state.

A study has been carried out into the formation of nanocrystalline grains during high-pressure torsion (HPT) deformation of Zr₆₅Cu₁₇Ni₅Al₁₀Au₃ bulk alloys prepared using tilt casting. As a preliminary to this, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were carried out on as-cast Zr_65+xCu_17-xNi₅Al₁₀Au₃ (x=0~5 at.%) and Zr₆₅Cu₂₀Ni₅Al₁₀Au₃ alloys, in order to determine the effect on the microstructure of the excess Zr content x and the presence of Au. From the XRD patterns, it was determined that all of the alloys had a metallic glassy nature. For Zr₆₅Cu₁₇Ni₅Al₁₀Au₃, the DSC results indicated the presence of a wide supercooled liquid region between the glass transition temperature (T_g) of 644 K and the crystallization temperature of 763 K, where the stable body-centered tetragonal Zr₂Cu phase was formed. In contrast, for the Zr_65+xCu_17-xNi₅Al₁₀Au₃ alloys, precipitation of an icosahedral quasicrystalline phase (I-phase) was observed in the supercooled liquid region at about 715 K. HPT deformation of the Zr₆₅Cu₁₇Ni₅Al₁₀Au₃ alloys was carried out under a high pressure of 5 GPa. Both as-cast specimens and those annealed at T_g-50 K for 90 min were used. Following a single HPT rotation (N=1), transmission electron microscopy identified the presence of face- centered cubic Zr₂Ni precipitates in the as-cast alloy, with a size of about 50 nm. For the annealed alloy, a high density of I-phase precipitates with sizes of less than 10 nm was observed following HPT with N=10, indicating that the combination of severe plastic deformation and annealing is effective at producing extremely small grains.

The effect of back pressure during equal channel angular pressing on thermal stability of Electrolytic Tough Pitch (ETP) copper was studied. The thermal behavior was assessed by means of microhardness measurements and microstructure characterization of the deformed samples at various stages of annealing. The assessment of the variation of the recrystallized fraction of the material with annealing was also carried out using a relatively new method based on internal misorientation measurements by EBSD technique. A higher stored energy and lower activation energy for recrystallization in the case of a back pressure of 100 MPa was obtained by means of DSC analysis. As a main outcome of this work, it was found that application of back pressure reduces thermal stability of the UFG microstructure. However, the effect is relatively small and does not negate the advantages of processing with back pressure in terms of the degree of grain refinement and strength enhancement.

As-cast Cu-0.7wt% Cr and Cu-1.0wt% Cr alloys were subjected to equal-channel angular pressing (ECAP), hard cyclic viscoplastic (HCV) deformation and post deformation heat treatment for receiving an ultrafine grained material with a combination of high strength, good wear resistance and high electric conductivity. Samples from Cu-0.7wt% Cr alloy were processed up to six passes and Cu-1wt% Cr alloy samples were processed up to four passes of ECAP via B_c route. HCV deformation of samples was conducted by frequency of 0.5 Hz for 20 cycles at tension-compression strain amplitudes of ±0.05%, ±0.1%, ±0.5%, ±1% and ±1.5%, respectively. During HCV deformation, as-cast Cu-0./wt% Cr alloy show fully viscoelastic behavior at strain/stress amplitude of ±0.05% while ECAP processed material show the same behavior at strain amplitude of ±0.1%. The Young modulus was increased from ~120 GPa up to ~150 GPa. The results illustrated that specific volume wear decrease with increasing of hardness but the measured coefficient of friction (COF ~ 0.6) was approximately the same for all samples at the end of wear testing. The hardness after ECAP for 6 passes by Bc route was 192HV0.1 and electric conduction 74.16% IACS, respectively. By this the as-cast Cu-0./wt% Cr alloy (heat treated at 1000 °C for 2h) has microhardness ~70HV0.1 and electrical conductivity of ~40% IACS. During aging at the temperatures in the interval of 250-550 °C for 1h the hardness and electrical conductivity were stabilized to mean values of 120±5HV0.1 and to 93.4±0.3% IACS, respectively. The hardness and electric conductivity took decrease by temperature increase over ~550 °C, respectively. The results of present experimental investigation show that UFG Cu- 0.7wt% Cr alloy with compare to Cu-1.0% Cr alloy is a highly electrical conductive and high temperature wear resistant material for using in electrical industry.

Recently it has been demonstrated that nanolayered hcp/bcc Zr/Nb composites can be fabricated with a severe plastic deformation technique called accumulative roll bonding (ARB) [1]. The final layer thickness averaged to approximately 90 nm for both phases. Interestingly, the texture measurements show that the textures in each phase correspond to those of rolled single-phase rolled Zr and Nb for a wide range of layer thickness from the micron to the nanoscales. This is in remarkable contrast to fcc/bcc Cu/Nb layered composites made by the same ARB technique, which developed textures that strongly deviated from theoretical rolling textures of Cu or Nb alone when the layers were refined to submicron and nanoscale dimensions. To model texture evolution and reveal the underlying deformation mechanisms, we developed a 3D multiscale model that combines crystal plasticity finite element with a thermally activated dislocation density based hardening law [2]. For systematic study, the model is applied to a two-phase Zr/Nb polycrystalline laminate and to the same polycrystalline Zr and polycrystalline Nb as single-phase metals. Consistent with the measurement, the model predicts that texture evolution in the phases in the composite and the relative activities of the hcp slip modes are very similar to those in the phases in monolithic form. In addition, the two-phase model also finds that no through-thickness texture gradient develops. This result suggests that neither the nanoscale grain sizes nor the bimetal Zr/Nb interfaces induce deformation mechanisms different from those at the coarse-grain scale.

The use of severe plastic deformation techniques for processing magnesium alloys has moved from the early difficulties of processing to a stage of tailoring the best properties of these materials. The present paper reviews processing, structure and mechanical properties characterization. It is shown that ultrafine-grained structures are obtained in magnesium alloys processed by multiple passes of Equal-Channel Angular Pressing at moderate temperatures. Ultrafine-grained structures are also obtained by room temperature processing by High- Pressure Torsion. The ultrafine-grained structures increase strength and introduce excellent superplastic capabilities in many magnesium alloys. Moreover, processing magnesium alloys by severe plastic deformation leads to the development of anisotropy in mechanical behavior.

Metals produced by Severe Plastic Deformation (SPD) offer distinct advantages for medical applications such as orthopedic devices, in part because of their nanostructured surfaces. We examine the current theoretical foundations and state of knowledge for nanostructured biomaterials surface optimization within the contexts that apply to bulk nanostructured metals, differentiating how their microstructures impact osteogenesis, in particular, for Ultrafine Grained (UFG) titanium. Then we identify key gaps in the research to date, pointing out areas which merit additional focus within the scientific community. For example, we highlight the potential of next-generation DNA sequencing techniques (NGS) to reveal gene and non-coding RNA (ncRNA) expression changes induced by nanostructured metals. While our understanding of bio-nano interactions is in its infancy, nanostructured metals are already being marketed or developed for medical devices such as dental implants, spinal devices, and coronary stents. Our ability to characterize and optimize the biological response of cells to SPD metals will have synergistic effects on advances in materials, biological, and medical science.

This paper presents an overview and some original results about the microstructure evolution of an Ultra Fine Grained (UFG) nickel-iron based alloy INCONEL 718 processed by Severe Plastic Deformation (SPD). The ultrafine grain structure of this alloy that contains a high density of γ" and γ' precipitates was characterized by Scanning Transmission Electron Microscopy (STEM). We propose a comparison between two SPD processes, High Pressure Torsion (HPT) and Multiple Forging (MF). The grain refinement is much more pronounced by HPT but intermetallic particles are partly dissolved during SPD. The UFG structure after MF is obviously very different and exhibits a much better thermal stability especially because second phase particles do not reprecipitate during post-deformation annealing.