Evolution of elastic constants of the NiTi shape memory alloy during a stress-induced martensitic transformation

We carried out an in situ ultrasonic characterization of a NiTi shape memory alloy polycrystal subjected to pseudoplastic straining. The measurement leads to a full elastic tensor of the transversely isotropic polycrystal during the stress-induced austenite -> R-phase -> B19' martensite transformation. The results reveal a strong anisotropy of the R-phase already in the low-strain state, which is then retained in character throughout the R-phase -> martensite transition and even in the stress-free oriented martensite after the unloading. By using a micromechanical model based on homogenization approaches, we show that this strong anisotropy is probably related to twin boundaries both in the R-phase and in martensite rather than to the anisotropy of the unit cell and the crystallographic texture. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

An in situ ultrasonic characterization was carried out on a NiTi shape memory alloy polycrystal under pseudoplastic straining, revealing a strong anisotropy during the transformation process, possibly related to twin boundaries.