Change in the Phase Composition of a NiTi-Based Alloy during the Implementation of the Shape Memory Effect

The relationship by mass between phase transformations upon heating and cooling of Ti–55.6% Ni alloy in a state aged in various modes with its shape change during the implementation of a one-way shape memory effect has been studied. It is shown that shape restoration occurs in two stages after deformation at –10°C with 2% bending, In this case, one stage is characterized by a small (0.3–0.4%) restored deformation and the other stage by a large deformation value (1.0–1.1%). A small part of the deformation (0.3–0.4%) is eliminated at the low-temperature stage of shape restoration after two hours of aging at 520°C and two-stage processing at 520 + 460°C and at the high-temperature stage after aging at 460°C. X-ray diffraction tests showed that the duration of the first and second stages of shape change depended on the sequence of occurrence and/or the superposition of R → B2, B19' → R and B19' → B2 transformations during heating.