Effect of annealing on stress-induced transformation behaviors at low temperatures in a Ti–51.8 at.% Ni shape memory alloy



For polycrystalline Ti-51.8Ni (at.%) specimens annealed at 473 and 943 K, the microstructures at room temperature were observed by transmission electron microscopy and the stress-induced transformation behaviors at low temperatures were investigated by compressive test. The precipitation of Ti3Ni4 was confirmed in the both annealed specimens, where the precipitates at 943 K had a lenticular shape in micrometer size, and those at 473 K seemed to be clusters in nanometer size. Superelasticity with almost complete shape recovery was detected at temperatures below 200 K for all the annealed specimens. In comparison to the as-homogenized specimen, although the temperature dependence on the stress hysteresis only slightly changed in each annealing condition, the equilibrium stresses in the specimen annealed at 473 and 943 K apparently increased and decreased, respectively.