Methods of Research of Shape Memory Effect and Superelasticity in the Alloy Ti-22%Nb-6%Zr

Abstract

Cyclic tensile tests were carried out as applied to annealed foils of the superelastic Ti-22Nb-6Zr alloy (at.%) as well as indentation of these foils with an increasing amplitude of indenter intrusion in the sample at temperatures lowering from 20∘ down to -60-70∘C. Mechanical tests were performed on samples cut along andacross the rolling direction. According to the results of measurements of mechanical properties, it is established that during cyclic stretching of foils in the rolling direction, superelasticity manifests itself, and also material training is observed with subsequent preservation of the maximal renewable deformation. When the foil is loaded in the transverse direction, no superelasticity is observed, moreover, some samplesare destroyed even with a deformation of 2%. With a decrease in the annealing temperature of foils, the curve of the continuous change of loading with the depth of indenter penetration undergoes substantial changes, which indicate the appearance of a superelastic deformation under the indenter. Curves of monotonic loading and discharge undergo an inflection, and the plastic deformation region is substantially reduced. From the discharge curves in this case, we can calculate two elastic modules, typical for the usual elasticity and superelastic behavior of the alloy. In general, the main characteristics of the continuous indentation curve depend on the amount of the martensitic phase. The dependence of the modules of elasticity for foils, coolingdown to -(60-70∘C), and for their subsequent heating up to the room temperature is constructed