The effect of thermal and mechanical cycling on structural and phase transformations and properties of metastable (+) shape memory alloy Cu–39.5 wt% Zn is investigated. The temperatures of the onset and end of the direct and reverse martensitic transformation in the Cu–39.5 wt% Zn alloy are determined from the temperature dependences of electrical resistance. Mechanical properties are measured in mechanocyclic tensile cryotests. The structure and phase transformations are studied by optical, scanning and transmission electron microscopy and X-ray phase analysis. An increase in the critical temperatures of the onset of direct thermoelastic martensitic transformations with an increase in the number of “cooling-heating” thermal cycles is found. The features of tweed contrast in electron microscopic images and diffuse effects in microelectron diffraction patterns are analyzed depending on the number of thermal cycles. An increase in the dislocation density during thermal cycling through the martensitic transition temperature was established, and their role in stabilizing the temperatures of phase transformations and the shape memory effect was explained. During mechanical cycling in the martensitic state, the ferroelasticity effect was discovered.
A.E. Svirid (Wed,) studied this question.