Kinetics and thermodynamics of the shape-memory effect in martensitic NiTi and (Ni1−xCux)Ti alloys

By rapid pulse heating of NiTi-based shape-memory wires, both with and without an applied load, the details of the recovery process have been studied. It is shown that, contrary to existing theories, the temperature of the reverse transformation is relatively independent of applied load. A modified hypothesis for the motion is proposed, taking into account internal stresses present in polycrystalline material. Without applied load, the reverse-phase transformation on heating is measured to occur within 3 ms, and motion under load is shown to be largely governed by the mechanical time needed to move the weight.