Development of methods of severe plastic deformation for the production of high-strength alloys based on titanium nickelide with a shape-memory effect

A brief review of the investigations of the authors concerning the application of methods of severe plastic deformation (SPD) for the production of nanostructured alloys on the basis of titanium nickelide with a thermomechanical memory is presented. For the first time, high-strength nanostructured TiNi-based alloys were obtained using several different SPD techniques, including (1) multiple torsion under a high pressure, (2) multiple equal-channel angular pressing, and (3) multiple deformation by rolling and drawing with intermediate annealings. It is shown that a special place among these techniques belongs to the process of controlled nanocrystallization during annealing of alloys in the initially amorphous state that is ensured by severe cold plastic deformation. The main features of structural states of SPD-processed alloys and their thermal stability are analyzed using X-ray diffraction and transmission electron microscopy, including experiments in situ. The time temperature conditions of nanocrystallization of amorphous TiNi-based alloys and the critical temperatures and sequence of martensitic transformations were established and their dependence on the mode and amount of deformation and average grain size was determined. The main structural mechanisms of the nucleation and growth of martensitic phases (R, B19', and B19) and their morphology in nanostructured SPD-processed alloys based on TiNi were revealed. The temperature dependences of the electrical resistivity and the mechanical properties of nanostructured alloys subjected to severe plastic deformation were measured.