TRANSFORMATION AND DEFORMATION CHARACTER- ISTICS OF Ti_(49 4)Ni_(50.6) SUPERELASTIC SPRING

Effects of the annealing and deforming temperatures, thermal cycle, and the stress-strain cycle on the transformation and deformation characteristics of Ti49.4Ni50.6 superelastic (SE) coil spring have been investigated by means of differential scanning calorimetry, tensile test, and stress-strain cycling test. The phase-transformed type of the cold worked plus intermediate temperature annealed TiNi alloy is parent phase B2 R phase martensite B19' during cooling heating cycle. The martensitic transformation temperatures increase and the .R-phase transformation temperatures decrease with increasing the annealing temperature. The SE property can be obtained at room temperature for the 623-773 K annealing Ti49.4Ni50.6 alloy spring, and the rigidity of the SE spring increases with increasing the deformed temperature. The SE property of Ti49.4Ni50.6 alloy spring weakens while the annealed temperature is over 823 K. The smaller the taken shear strain, the higher the strain recovery rate of TiNi SE spring is during the thermal cycle. The prior cyclic training can enhance the SE stability of TiNi alloy spring.