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 degrees 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 degrees 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%. (c) 2006 Elsevier B.V. All rights reserved.