Structure and Properties of the Ti–50.0 at%Ni Alloy after Strain Hardening and Nanocrystallizing Thermomechanical Processing

Abstract

The thermomechanical processing consisting in cold work (true strain e=0.3–1.9) followed by a post-deformation annealing (200–700°C temperature range) is applied to the equiatomic Ti–Ni alloy. The evolution of the structure, substructure and functional properties of the material is studied. For all levels of cold work, the maxima of the free recovery strain and constraint recovery stress are obtained after annealing in the 350–400°C temperature range. For a moderately cold-worked material (true strain e=0.3), this temperature range corresponds to polygonization; for a severely cold-worked material (e=1.9), it corresponds to the material nanocrystallization, while for a highly cold-worked material (e=0.88), the structure is mixed. An increase in the cold-work strain leads to an increase in the completely recoverable strain above 8% and in the maximum recovery stress up to 1450 MPa, as well as to the widening of the superelastic temperature range.