Effects of Thermo-mechanical Treatment on the Shape Memory Effect and the Pseudoelasticity of Ti-50.2Ni and Ti-47.5Ni-2.5Fe Alloys

Abstract

Effects of thermo-mechanical treatment on the shape memory effect and the pseudoelasticity of a near equiatomic Ti-50.2Ni (at%) and a ternary Ti-47.5Ni-2.5Fe (at%) alloy were investigated by tensile tests for specimens which were cold rolled and subsequently annealed at temperatures between 400°C and 600°C. It has been found that at least 20% of cold working followed by 400°C annealing is necessary for perfect pseudoelasticity to occur in the Ti-50.2Ni (at%) at temperatures above A_f. By optical and electron microscope observations, it has been found that a high density of dislocations introduced by cold working and rearranged by annealing below the recrystallization temperature is effective to raise the critical stress for slip deformation and thus to improve the shape memory effect and the pseudoelasticity.
It has been found for the ternary Ti-47.5Ni-2.5Fe (at%) alloy that the thermo-mechanical treatment improves the shape memory effect associated with the R-phase.