Microstructural evolution and related mechanisms in NiTiCu shape memory alloy subjected local canning compression

Abstract

The microstructural evolution and related mechanisms in NiTiCu shape memory alloy (SMA) subjected to severe plastic deformation (SPD) were investigated based on local canning compression. During the local canning compression, the NiTiCu SMA experiences four stages, which involve the elastic accommodation of martensite variants, the inelastic deformation process induced by martensite reorientation and detwinning, the elastic deformation of martensite phase and the plastic deformation of martensite phase. During the plastic deformation, dislocation slip is activated firstly, and then twinning deformation is induced to accommodate the further deformation. When the density of deformation twins reaches saturation state, shear bands are generated to accommodate the further increasing strain. Under the shear banding deformation, the twins in the shear bands are broken into fine-equiaxed grains accompanied with local amorphization. The new rounds of shear banding deformation result in the further grain refinement and the fraction increase of amorphous phase. The refined microstructures of the NiTiCu SMA are induced by two essential processes, which involve the formation of thin lath structures split from elongated laths and the breakdown of thin lath structures by transverse dislocation walls composed of high density of dislocations.