Influence of thermo- and mechanocycling of thermoelastic martensitic transformations on the microstructure and properties of metastable $(\alpha+\beta)$ copper-zinc-based shape memory alloys

The results of studies of the effect of thermal and mechanical cycling on structural and phase transformations and properties of metastable microduplex $\alpha + \beta$ alloys with the shape memory effect of Cu-(38-41)wt%Zn are summarized. The temperature dependences of electrical resistance are presented and the temperatures of the start and finish of the direct and reverse martensitic transformations in alloys are determined. According to the tensile test data, mechanical properties were obtained. The structure and phase transformations have been studied using scanning and transmission electron microscopy and X-ray phase analysis. The features of tweed contrast on electron microscopic images and diffuse effects on electron diffraction patterns are analyzed depending on the number of thermal cycles and an increase in dislocation density during thermal cycling through a martensitic transition is established. An increase in the critical temperatures of the start of direct thermoelastic martensitic transformations with the number of thermal cycles "cooling-heating" and the effects of ferroelasticity were found. The stabilization of the temperatures of phase transformations and the shape memory effect during thermal and mechanical cycling of alloys is associated with the phenomenon of phase hardening during thermoelastic martensitic transformation.