Study On Cold-Workability Of R-Phase In Niti Shape Memory Alloy

NiTi shape memory alloy is considered to be the most important shape memory alloys in industries and physic for its salient superelasticity and shape memory effect. The cold-workability and phase transformation characteristic in Ti-50.8atNi% shape memory alloy was investigated. The investigation showed that the NiTi shape memory alloy is subjected to appropriate pre-tension and aging, the cold-workability of Ti-50.8atNi% shape memory alloy is excellent when the specimen was solution-treated,10% pre-tension followed by ageing at 500 ℃. Meanwhile, the microstructure of this alloy consists of R-phase.Further investigation showed that different deformation has little effect on reverse martensitic phase transformation temperatures ( As,Af) on the NiTi shape memory alloy which consists of R-phase. The reverse martensitic phase transformation temperatures ( As,Af) are below body temperature.The reverse martensitic phase transformation temperature As are below body temperature when ageing at 300℃ after different deformation while the reverse martensitic phase Af increases with the increasing deformation of the specimen. The shape memory effect of Ti-50.8atNi% shape memory alloy can not be used in human body when ageing at 400 ℃ and 500 ℃ because the transformation temperatures( As,Af) are beyond body temperature.