Atomistic simulations on orientation dependent martensitic transformation during nanoindentation of NiTi shape-memory alloys

Abstract

Unusual orientation-dependent mechanical responses during nanoindentations of nickel-titanium shape-memory alloys are studied by performing a series of large-scale molecular dynamics simulations. By analyzing the mechanical responses of single crystal nickel-titanium shape-memory alloys during indentations along [1 1 1] and [0 0 1] directions, the present study provides direct supporting results emphasizing the importance of the anisotropy in the martensite formation. The microstructural evolution, especially for the martensitic transformation beneath the indenter tip, is clearly visualized and directly related to the indentation load-depth curves and the surface profile. The results show that the reported orientation-dependency of the indentation load-depth curves is decisively driven by the anisotropy in the preferred growth direction of the martensite phase and the amount of the martensite phase formed beneath the indenter tip.