J. Pfetzing, M. F. -. X. Wagner, D. Peter, G. Eggeler, Ruhr-University Bochum, Bochum, Germany
Nanoindentation is an appropriate method to characterize the local mechanical behavior of NiTi shape memory alloys. Mechanical anisotropy is known from macroscopic uniaxial experiments with NiTi single crystals. In the present study we investigate whether grain orientations influence the mechanical behavior of NiTi during indentation of single grains. Nanoindentation is systematically performed on B2 NiTi grains with <001>, <101> and <111> orientations. Load-displacement data, elastic moduli, and hardness values are investigated and compared with nanoindentation results of B2 NiAl, which only deforms elasto-plastically. Additional microstructural investigations below the indented surface are performed to directly analyze the deformation mechanisms of differently oriented grains. The study shows that grain orientation has a considerable effect on the nanoindentation behavior of pseudoelastic NiTi, whereas such a significant influence during nanoindentation of an elasto-plastic NiAl is not observed. These results indicate that orientation-dependencies in NiTi are related to a stress-induced martensitic transformation below the indenter tip.
Summary: In this study nanoindentation is systematically performed on B2 NiTi grains with <001>, <101> and <111> orientations to investigate whether grain orientations influence the mechanical behavior of NiTi during indentation of single grains. Our results show that grain orientation has a considerable effect on the nanoindentation behavior of pseudoelastic NiTi, which is due to a stress-induced martensitic transformation below the indenter tip.
