Investigation of Nucleation and Growth of Detwinning Mechanism in Martensitic Single Crystal NiTi Using Digital Image Correlation

In this study, the deformation of martensitic NiTi was investigated utilizing single crystal Ti-50.1 at.% Ni in [123], [111], and [001] orientations. The stress-strain response of the martensitic NiTi was resolved experimentally using incremental tensile loading. The nucleation and growth of the detwinning mechanism was investigated by means of in-situ digital image correlation ( DIC) technique which enabled the precise determination of the onset of detwinning on the stress-strain curve. The mechanism of detwinning nucleation was observed before the stress plateau on the stress-strain curve. The use of DIC for the [123] orientation revealed that the intersection of twins causes more hardening through twinning-induced strains. Based on the stress-strain response of the [123], [111], and [001] orientations, it is obvious that detwinning is orientation independent. In contrast, the evolution of detwinning after nucleation is orientation dependent.