The microstructure and linear superelasticity of cold-drawn TiNi alloy

The microstructure and linear superelasticity of cold-drawn TiNi alloy have been investigated using CTEM, HREM and in-situ transition electron microscopy observations and tensile tests. The microstructural evolution procedure of the martensite variants with increasing degree of area reduction was found to be that the quantities of (111̄) Type I, (001) compound, (011) Type I and (111) Type I twinning plates increase gradually with decreasing the amount of the 〈011〉 Type II twinning bands. The corresponding dominant deformation mechanism changed from the coalescence of martensite variants to the reorientation of substructural bands inside martensite variants utilizing the most favorably oriented twin systems. The intrinsic reason for the linear superelasticity of the moderately cold-drawn TiNi alloy was confirmed to be associated with the appearance and disappearance of (001) microtwinning inside the 〈011〉 Type II substructural bands.