Development of High-Strength, Fine, and Ultrafine-Grained Shape Memory Alloys

Abstract

A brief review of the systematic studies of the structural and phase transformations and properties of alloys based on titanium nickelide and alloyed with Fe, Co, Cu, Zr, Hf, Pd, Pt, and Au is presented. Generalized phase diagrams of martensitic transitions are built. It is shown that alloying with a third component in a quasi-binary composition increases or decreases the critical temperatures of the thermoelastic martensitic transformations and shape memory effects (SMEs) to a different degree with respect to the base binary titanium nickelide. The structure of thermoelastic martensite is established to have a packet–pyramidal morphology of thin coherent nano- and submicrometer crystals. Martensite crystals are twinned over several systems of a “soft” twinning shear in an isotropic elastic–soft austenite. It is this mechanism that provides a unique coherent accommodation for the arising elastic stresses. The fine-grained (FG) and ultrafine-grained (UFG) structure hardens the alloys and increases their plasticity, while retaining the thermomechanical shape memory in them.