Specific Features of Deformation of the Nitinol Alloy After Electrolytic Hydrogenation

Abstract

Specific features of the effect of hydrogenation on the susceptibility of a Ni–Ti alloy with shape memory to deformation are determined with the use of metallographic, electrochemical, and mechanical studies. Three sections are detected in the tensile curves of the specimens of nickel–titanium alloy in the initial state. The first section is linear due to the elastic deformation of the alloy with initial austenitic structure. The second section is nonlinear and associated with pseudoelastic structural transformations of the original austenitic structure into a martensitic structure. The third section is also linear and caused by the elastic deformation of martensite formed in the course of deformation of austenite. After hydrogenation of the Ni–Ti alloy, the pseudoelastic structural transformation starts at a somewhat lower level of stresses than without hydrogenation. In this case, the specimens are destroyed after the termination of this transformation for a much lower level of plasticity than in the nonhydrogenated alloy. It is assumed that the electrolytic hydrogenation of the alloy promotes the formation of a very brittle hydride phase on the surface of Ti-type inclusions revealed in the structure of alloy in the initial state. Its thickness is determined by the duration of the process of hydrogenation rather than by the current used for hydrogenation.