Characterization of superelastic NiTi alloys by nanoindentation: Experiments and simulations

NiTi-based shape memory alloys are metallic materials exhibiting remarkable response to mechanical and/or thermal loading, e.g. superelasticity, pseudoplasticity or one-way shape memory effect. They can be engineered into structures of micro-size dimensions, hence, they appear promising for application in micro-electromechanical systems. For their efficient utilization, appropriate characterization is important. Due to relative simplicity, indentation represents a very standard and popular technique for basic characterization of metallic materials providing information about stiffness and hardness. Moreover, it can be used for identification of other events in the material. This study aims to verify applicability of the recently developed constitutive model for NiTi-based shape memory alloy in simulations of nanoindentation tests. The model is fitted to a particular sample material using experimental data, and a series of simulations mimicking tests at various temperatures is performed. Since the model also captures two-stage martensitic transformation via the intermediate R-phase, its influence on the simulations is investigated as well. It is confirmed that spherical indentation is a suitable method for simple and fast detection whether the material is in superelastic or pseudoplastic regime.