Phase transformation behaviors of prestrained TiNi shape memory alloy fibers under the constraint of a hard substrate

Abstract

The phase transformation behaviors of prestrained TiNi shape memory alloy (SMA) fibers under the constraint of a hard substrate were explored. By means of measuring the deformation of the substrate, it was found that the temperature when the recovery stress is generated upon second heating is much lower than that upon the first heating. The results of the differential scanning calorimeter (DSC) measurements indicated that after the first constrained heating–cooling process, the oriented martensite (M) in the TiNi alloy divided into two sorts of martensite, the deformed martensite (M1) and the inheriting deformation martensite (M2). The start temperature of the transformation from inheriting deformation martensite M2 to parent is lower than that of the transformation from oriented martensite (M) to parent. Therefore, upon the second heating the recovery stress generated at the lower temperature corresponds to the transformation from inheriting deformation martensite M2 to parent. The phase transformation behavior upon the third heating–cooling process is similar to the second one due to the almost identical DSC heating and elongation curves.