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 microsc opy observations and tensile tests. The microstructural evolution procedure of the martensite variants with increasing degree of area reduction was fo und to be that the quantities of (11(1) over bar) Type I, (001) compound, ( 011) Type I and (111) Type I twinning plates increase gradually with decrea sing the amount of the [011] Type II twinning bands. The corresponding domi nant deformation mechanism changed from the coalescence of martensite varia nts to the reorientation of substructural bands inside martensite variants utilizing the most favorably oriented twin systems. The intrinsic reason fo r the linear superelasticity of the moderately cold-drawn TiNi alloy was co nfirmed to be associated with the appearance and disappearance of (001) mic rotwinning inside the [011] Type II substructural bands. (C) 2000 Elsevier Science S.A. All rights reserved.