Texture evolution during nitinol martensite detwinning and phase transformation

Nitinol has been widely used to make medical devices for years due to its unique shape memory and superelastic properties. However, the texture of the nitinol wires has been largely ignored due to inherent complexity. In this study, in situ synchrotron X-ray diffraction has been carried out during uniaxial tensile testing to investigate the texture evolution of the nitinol wires during martensite detwinning, variant reorientation, and phase transformation. It was found that the thermal martensitic nitinol wire comprised primarily an axial (⁠$1¯20$⁠), (120), and (102)-fiber texture. Detwinning initially converted the (120) and (102) fibers to the (⁠$1¯20$⁠) fiber and progressed to a (⁠$1¯30$⁠)-fiber texture by rigid body rotation. At strains above 10%, the (⁠$1¯30$⁠)-fiber was shifted to the (110) fiber by (⁠$21¯0$⁠) deformation twinning. The austenitic wire exhibited an axial (334)-fiber, which transformed to the near-(⁠$1¯30$⁠) martensite texture after the stress-induced phase transformation.