Deformation Structure Evolution during Mechanical Cycling of Nanocristalline TiNi alloy

The influence of cyclic tensile deformation in the loading/unloading mode for up to 45 cycles in the superelastic loop region on the inelastic characteristics and deformation structure of the nanocrystalline aging superelastic alloy Ti–50.9 at % Ni is studied. It is established that the distinctive feature of the initial stage (up to 5–10 cycles) is the accumulation of dislocations and the formation of a three-dimensional network with nodes pinned by Ti3Ni4 particles, limiting the dislocation activity. Achieving a high level of stresses in the strengthened dislocation structure with an increase in the number of cycles to 10–20 contributes to a decrease in the shear stability of the B2 structure and the occurrence of additional accommodative deformation mechanisms. The result of the relaxation of internal stresses arising near the boundaries of primary grains and their joints is the formation of kink-like deformation bands, providing a collective nature of the reorientation of the crystal lattice.