The mechanical behavior of the binary polycrystalline NiTi alloy with a quasi-equilibrium structure has been considered in the course of the high-strain-rate extension in a temperature range of 20–300°C. The quasi-equilibrium structure, which is necessary to ensure the long-term stability of special properties of the alloy, was achieved using aging, after which both the forward and reverse martensitic transformations exhibited a multistage character and the phase composition at room temperature was characterized by the presence of R and B19′ martensites. To separate the contributions that come from the equilibrium structure and from the high rate of tension to the mechanical behavior of the alloy, a comparative analysis of the diagrams of high-strain-rate and quasi-static tension has been performed. It has been shown that the action of several mechanisms of reversible deformation is determined by the specific features of the equilibrium structure, and the level of stresses at which these mechanisms are developed is controlled by the rate of tension. The results of the X-ray diffraction study of the phase composition of the alloy samples after high-strain-rate tension, which make it possible to conclude that the mechanical behavior of martensite and austenite upon the dynamic tension of the alloy is determined by the development of stress-induced R → B19′, B2 → R, and B2 → B19′ transformations and by the processes of the detwinning and reorientation of crystals of B19′ martensite, are given.

The reversible two-way shape memory in TiNi alloy after straining in austenitic state was investigated. It is shown that such shape memory effect in titanium nickelide is the superposition of the two-way shape memory of austenitic and martensitic types. Thermal cycling invarious incomplete temperature ranges of the reversible martensitic transformation leads to the realisation of the two-way shape memory of austenitic and martensitic types independently of each other.