Fabrication of Ti-Ni alloys for proportional control

Phase transformation and deformation behavior of temperature-gradient annealed (TGA) equiatomic Ti-Ni alloy wires were investigated by means of differential scanning calorimetry (DSC), thermal cycling under constant load and tensile testing. TGA treatment in a temperature range of 658∼823 K caused variations of 10 K in T_R* and 14 K in M_s along the length of the specimen. Temperature dependence of specimen elongation (dε/dT) of TGA treated Ti-Ni alloy wires was in the range of 0.12∼0.43%/K depending on annealing temperatures. The lowest dε/dT was obtained in the sample annealed in the temperature range of 658∼713 K. The stress for martensite reorientation remained nearly constant for the specimen annealed in the temperature range of 740∼823 K, whereas that for the specimen annealed in the temperature range of 658∼740 K increased continuously with increasing strain.