The Rational Nature of Type II Twin in NiTi Shape Memory Alloy

Due to its irrational character, the atomic arrangement along the twin plane of h011i type II twin in NiTi shape memory alloy (SMA) has been an issue of disagreement over the past years. Understanding the atomic arrangement along the type II twin plane is important, both scientifically and practically, as it is strongly related to the lattice shear during martensitic transformation, the deformation mechanism of SMA, and the shape recovery associated with reverse phase transformation. The present research carefully studies the h011i type II twin plane through HRTEM observation, crystallographic analysis, atomic image simulation, and reexamination of the major reported HRTEM observations, providing convincing evidences that the irrational h011i type II twin is atomically rational.