On the crystallographic anisotropy of nanoindentation in pseudoelastic NiTi

0387730 - ÚFM 2013 RIV GB eng J - Journal Article
Pfetzing-Micklich, J. - Somsen, Ch. - Dlouhý, Antonín - Begau, Ch. - Hartmaier, A. - Wagner, M. F. X. - Eggeler, G.
On the crystallographic anisotropy of nanoindentation in pseudoelastic NiTi.
Acta Materialia. Roč. 61, JAN (2013), s. 602-616. ISSN 1359-6454. E-ISSN 1873-2453
R&D Projects: GA ČR GA106/09/1913
Institutional research plan: CEZ:AV0Z20410507
Keywords : NiTi * NiAl * Nanoindentation * Pseudoelasticity * Molecular dynamic simulations
Subject RIV: JG - Metallurgy
Impact factor: 3.940, year: 2013

We use a nanoindenter with a Berkovich tip to study local mechanical properties of two polycrystalline intermetallics with a B2 crystal structure, NiAl and NiTi. We use orientation imaging scanning electron microscopy to select a relevant number of grains with appropriate sizes and surface normals parallel to h001i, h101i and h111i. As a striking new result, we find a strong crystallographic orientation dependence for NiTi. This anisotropy is less pronounced in the case of NiAl. For NiTi, the indentation force required to impose a specific indentation depth is highest for indentation experiments performed in the h001i direction and lowest along the h111i direction. We consider transmission electron microscopy results from cross-sections below the indents and use molecular dynamics simulations and resolved shear stress calculations to discuss how this difference can be accounted for in terms of elementary deformation and transformation processes, related to dislocation plasticity (NiAl and NiTi), and in terms of the stress-induced formation and growth of martensite (NiTi). Our results show that the crystallographic anisotropy during nanoindentation of NiTi is governed by the orientation dependence of the martensitic transformation; dislocation plasticity appears to be less important. 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Permanent Link: http://hdl.handle.net/11104/0216689