Abstract:The microstructure, transformation, shape memory effect (SME) and superelasticity (SE) characteristics of Ti-50.8Ni shape memory alloy were investigated by thermal gravimetry, X-ray diffraction, optical microscopy, differential scanning calorimetry and tensile testing. The results show that the microstructure of Ti-50.8Ni alloy is fibrous after annealing below 600 oC, while it is equiaxed after annealing over 600 oC. The alloy oxidation speeds up when the heating temperature is over 600 oC. With the annealing temperature Ta increasing, the transformation types of Ti-50.8Ni alloy change from A→R→M/M→R→A to A→R→M/M→A to A→R/R→A (A—parent phase, R—R phase, M—martensite), the M transformation temperature increases, the R transformation temperature decreases, the M transformation temperature hysteresis decreases, and the alloy’s characteristics at room temperature change from SME+SE to SE. Ti-50.8Ni alloy spring shows SME+SE with deforming temperature Td＜20 oC, and it shows SE with Td＞30 oC. The stress-induced martensite stress of the alloy spring increases with increasing Td.