Nanomechanical properties of hardened 60NiTi

The nanomechanical properties of hardened 60NiTi were studied using nanoindentation. The hardened 60NiTi consists of two regions: the NiTi + Ni4Ti3 region, which is composed of a B2 NiTi matrix and nanoscale Ni4Ti3 precipitates, and the globular Ni3Ti precipitates. Blind nanoindentation was first performed on 60NiTi using a diamond Berkovich without differentiating the regions. The two regions were then selectively indented using a diamond cube corner nanoindenter. The results show that the elastic modulus and hardness of the NiTi + Ni4Ti3 region were similar to those of bulk 60NiTi. The Ni3Ti phase was found to have an elastic modulus that is more than double that of bulk 60NiTi and the NiTi + Ni4Ti3 region. The hardness was also found to be significantly higher. This study not only provides the first quantitative measurements of the mechanical properties of Ni3Ti precipitates within 60NiTi but also suggests that the presence of large amounts of easily imaged Ni3Ti could serve as a good indication of reduced amounts of Ni4Ti3, which could lead to lower overall hardness of the material. © 2020 Elsevier B.V.