TRANSFORMATION AND DEFORMATION CHARACTERISTICS OF Ti-50.8Ni-0.3Cr SUPERELASTIC ALLOY

Effects of annealing and deforming temperatures and the stress-strain cycle on the transformation,deformation and stress cycling characteristics of Ti-50.8Ni-0.3Cr superelastic(SE)al- loy wires and coil springs were investigated by DSC,XRD,tensile test and cycling test.The 350-600℃annealing Ti-50.8Ni-0.3Cr alloy shows SE property at the room temperature,and the microstructure at the room temperature consists of parent phase(B2)and TiNi_3.The annealing temperature in- fluences remarkably transformation type of the alloy.With increasing the annealing temperature the martensitic(M)transformation temperature increases,the R transformation temperature increases firstly then decreases,and the stress-induced M stress decreases firstly then increases.With increasing the deforming temperature the stress-induced M critical shear stress of the SE spring increases.The recovery ratio declines quickly at beginning of the stress-strain cycle,and then slowly with increasing of cycle number.The prior cyclic training can enhance the SE stability of the alloy spring.To obtain stable SE property for the alloy spring,the annealing temperature should be 400-550℃,and the using temperature should be over room temperature.