Interrelations between the properties and structure of thermomechanically-treated equiatomic Ti–Ni alloy

Thermomechanical processing with extended deformation and temperature ranges and their influence on the structure and properties of the equiatomic Ti–Ni shape memory alloy are studied using transmission electron microscopy, differential scanning calorimetry, electrical resistivity, tensile and specialized thermomechanical testing techniques. The deformation range covers e = 0.3–1.9 logarithmic thickness reduction, while the annealing temperature is varied from 200 to 700 °C in order to explore the possibility of creating a nanocrystalline material through conventional cold-rolling. 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 the moderately-to-highly cold-worked material (true strain e = 0.3–0.88), this temperature range corresponds to polygonization, while for the severely cold-worked material (e = 1.9), it corresponds to the material nanocrystallization. Nanocrystalline Ti–50.0 at.% Ni alloy generates recovery stresses of 1450 MPa, and completely recoverable strains above 8%.