Twinning and detwinning of 〈0 1 1〉 type II twin in shape memory alloy

Abstract 〈0 1 1〉 type II twin is a major twinning mode frequently observed in NiTi shape memory alloy. Its response to applied stresses is responsible for various inelastic deformation processes. In order to predict the shape recovery characteristic under various conditions, it is of primary importance to predict the martensite detwinning characteristic prior to the reverse transformation. However, due to its irrational nature, the type II twin plane is not as easily comprehensible as that of other types of twins and a strong disagreement exists over the nature of the twin boundary. In the present research, the 〈0 1 1〉 type II twin boundary before and after deformation was investigated. A complete model of 〈0 1 1〉 type II twin plane and its role in the detwinning process are proposed which can be used to account for the various experimental observations.