Key Engineering Materials Vol. 662

Abstract: The concentrated elastic-plastic contact was studied on a thin disc loaded by axial pressure in the central part. Components of energies and stresses were determined via a simple model and discussed.

Abstract: The Oliver–Pharr method has extensively been adopted for measuring hardness and elastic modulus by indentation techniques. However, the method assumes that the contact periphery sinks in, which limits the applicability to the materials pile-up [1]. This study proposes an improved methodology to calculate the real mechanical characteristics of individual phases in various steels with significant pile-up. Pile-up correction of mechanical characteristics is based on ratio of pile-up height and contact depth. Pile-up height was measured by atomic force microscopy (AFM). The effect of grain boundaries on the shape and size of the pile-up lobes was also discussed.

Abstract: In this work, correlation between nanomechanical properties and crystallographic orientation of grains in 99.9 % magnesium is presented. Crystallographic orientation of individual grains was obtained by scanning electron microscope (SEM) equipped with electron backscatter diffraction (EBSD) detector. Hardness and elastic modulus of grains with known orientation were subsequently determined by in situ nanoindentation in SEM. We show that hardness decreases with increasing angle between the direction of indentation and the c-axis of grains, while elastic modulus varies non-monotonically.

Abstract: In this work the influence of the thermal treatment on the local mechanical properties of model diluted Cu-Co alloys with Co content of 4 at.% is investigated. The samples underwent annealing at 1273 K followed by water quenching. The further thermal treatment at 1073 K of the oversaturated solid solution generated a fine distribution of Co-rich precipitates. Parameters of microstructure were evaluated by means of analytical electron microscopy. The nanoscale mechanical properties of precipitates, areas adjacent to the precipitates and precipitate-free zones were studied using large area grid indentation tests. Moreover, the modulus mapping capability was applied to obtain quantitative maps of the storage and loss stiffness and modulus.

Abstract: Nanoindentation and thermomechanical experiments on three types of metallic glasses with different glass forming ability were carried out. The nanoindentation behaviour at room temperature was associated with the creep at elevated temperatures. Different discontinuity populations and their shape observed on the nanoindentation loading curves were compared with morphology of plastic deformed indent regions. The influence of the differences in thermal stability of studied alloys on the nanoindentation in these alloys were studied as well.

Abstract: Nanoindentation experiments at the loading rates from 0.05 to 100 mN.s^-1 on the amorphous FeNiB alloy were executed. We found that the serrations in the load-displacement (P-h) curve are more pronounced at lower loading rates and gradually disappear upon increasing loading rate. We have estimated the contribution of the inhomogeneous plastic deformation from pop-in events on the P-h curves. The pop-in population was compared with the morphology of indents.

Abstract: Calibration of Berkovich indenter area function was performed on materials with different elastic-plastic behavior resulting in pile-up and sink-in, respectively. Experimentally obtained results were compared with the results obtained by the application of theoretical area function. The values of Young’s modulus and hardness were significantly affected by the calibration function used. Since the effects of pile-up and sink-in are already included in the used area function, this simple method can lead to more accurate results of Young’s modulus and hardness measurements.

Abstract: The paper participates in a development of composites. A composite tungsten-steel is studied as materials suitable for a first wall of tokamak, a composite FeAl + Al₂O₃ is a possible material for fourth generation of a nuclear power plant and a composite Al₂O₃ + YSZ is a potential implant material. The focus of our study is change of material properties near the interface and a determination of area size which is influenced by the adjacent material. Material properties are investigated by nanoindentation. The task is simulated using finite element method. Simulated specimen is composed of a tungsten part and a steel part. The sharp boundary between materials is a plane which is located parallel to the loading force direction. Elastic modulus is determined in dependence of a distance between the interface and a tip of the indenter. The simulated results are verified experimentally.

Abstract: The aim of this study is to investigate the influence of hydrogen on the microstructure and mechanical properties of Zr1Nb fuel cladding after high-temperature oxidation. As-received or pre-hydrided materials were tested. The influence of different cooling rates was examined as well. The microstructure was observed using of light microscopy. Oxygen distribution was measured using X-ray microanalysis. Local mechanical properties were determined by the microhardness and nanohardness measurements. Ring compression testing (RCT) was employed with the aim to obtain the macroscopic mechanical properties. Fractographic analysis was performed after the RCT. The experimental results confirmed that hydrogen as well as the cooling rate substantially influenced the microstructure and affected both local and macroscopic mechanical properties.