On the superelastic behavior during spherical nanoindentation of a Ni-Ti shape memory alloy

Nanoindentation, the most widely-used probe for small-scall mechanical property evaluation, has been increasingly adopted for exploring the local behavior of shape memory alloys (SMAs). Herein, we explore the influence of the testing parameters (i.e., peak load, indenter radius, loading/unloading rate, and cyclic loading) on the superelastic behavior of a Ni-Ti SMA at room temperature, at which it is in the austenitic state, during spherical nanoindentation. The possible underlying mechanisms for measured response due to each of the testing parameters are discussed in terms of the roles of forward/reverse stress-induced phase transformations, dislocation activity, latent heat evolution, and geometric compatibility of the interfaces during the post-yield deformation.