Transformation behavior of a Ti-47Ni-3Cu alloy heat treated under temperature gradient

Abstract

Transformation behavior and shape memory characteristics of temperature gradient anneal (TGA) treated and thermo-mechanically treated (TMT) Ti-47Ni-3Cu(at.%) alloys were investigated by means of differential scanning calorimetry and thermal cycling tests under constant load. Both TGA treated and TMT Ti-47Ni-3Cu alloys showed B2-B19' transformation behavior. The change in M-s* by 23K was developed in the TGA treated Ti-47Ni-3Cu alloy along the length of the sample (150 mm). TGA treated Ti-47Ni-3Cu alloy showed perfect shape memory effects. The temperature dependence of elongation (d epsilon/dT) of a TGA treated specimen was in the range of 0.02-0.09% K-1 depending on the amount of applied stress, which was small compared to that of a TMT specimen (0.01-0.18% K-1). The temperature dependence of elongation (d epsilon/dT) of the TGA treated specimen on cooling is almost the same as that on heating, while d epsilon/dT of the TMT specimen on cooling is much smaller than that on heating (0.68% K-1).