Shear deformation behavior of the austenitic Σ3{1 1 2} twin boundary in NiTi shape memory alloy: An atomistic study

Molecular dynamics simulations are performed to study the deformation behavior of the austenitic Σ3{1 1 2} twin boundary (TB) of NiTi alloy under shear loading along different directions at 550 K, which is above the austenite finish temperature (535 K). The results show that the Σ3{1 1 2} TB retards the stress induced martensitic transformation (SIMT) when the TB is sheared along [1 1¯ 0] but promotes the SIMT when it is sheared along [1 1 1¯], which is perpendicular to [1 1¯ 0]. This direction dependence is related to the favorable transformation plane and the lattice correspondence between B2 austenite and B19′ martensite. Besides, the shear directions can be divided into four groups according to the martensite nucleation and growth processes. What is more, B19′ may nucleate firstly in the grain's interior or from the TB depending on the resolved shear stress. These findings are valuable for the design and application of NiTi alloy devices.