Effects of Heat Treatment on Transformation and Shape Memory Behavior of Ti-49. 8Ni Cold-drawn Wire

摘要

Effects of heat treatment on transformation, tensile properties and shape memory behavior for Ti49. 8Ni(at %) cold-drawn wire were investigated by differential scanning calorimeter (DSC) and tensile tests. The results indicated that A→R→M transformation had occurred on cooling when the annealing temperature was less than 723K,and M→R transformation and R-?A transformation overlapped on heating. When the annealing temperature was between 773K and 873K,only M?←→A transformation occurred. The plasticity of the alloy wire was obviously improved after annealing at temperatures between 723K and 873K. The elongation reached its maximum after 823K annealing. The tensile strength maintains a high level of over 1000 MPa when the annealing temperature is less than 823K. The recovery strain and stress were the highest after annealing at 673K. The recovery strain reached its maximum of 6. 8% with a pre-strain of 15%,and the recovery stress was maximal at 1022 MPa with a prestrain of 9%.