Low-Temperature Aging in Nanocrystalline Ti-50.9 at% Ni Alloy

The effect of low-temperature annealing at 300 degrees C on aging of B2 solid solution in the mixed grain/subgrain structure of nanocrystalline Ti-50.9 at% Ni alloy is studied by transmission electron microscopy. The size, morphology and nature of distribution of Ti3Ni4 particles formed in the process of the low-temperature aging are determinted. The presence of dislocations inside both nanosubgrains and nanograins promotes the precipitation of Ti3Ni4 by heterogeneous mechanism. It is shown that initial non-uniform grain/subgrain structure of the nanocrystalline TiNi alloy contributes to inhomogeneous Ti3Ni4 precipitation in the nanostructure. The localization of dispersed coherent Ti3Ni4 precipitates at dislocations facilitates their blocking and effective hardening of B2 austenite, which ensures superelastic behavior of the material.