Effect of mechanical expanding on strain recovery characteristics and microstructures of TiNiNb shape memory alloy

摘要

The effect of mechanical expanding deformation on the strain recovery characteristics and microstructures of ring-shaped TiNiNb shape memory alloy were studied by cryogenic expanding tests and TEM observation. The results show that there exists a characteristic strain range (around 18%) at a certain deformation temperature (around -40 　℃), in which the transformation hysteresis of TiNiNb alloy is effectively increased and the shape recovery ratio keeps relatively high. There exists different morphologies of the stress-induced martensite (SIM) in the outer layer and in the inner layer for the specimen deformed to 18% at -40 　℃. The SIM variant are regularly arranged in the outer layer whose submicrostructure is (111) twin of type Ⅰ, whereas it exhibits cross-hatch morphology in the inner layer whose submicrostructures are (111) twin of type Ⅰ and (001) compound twin.