Study on phase transformation, internal stress and texture evolution of cold drawn Nb nanowire-NiTi composite wires upon annealing

Abstract

Phase transformation, internal stress and texture evolution of cold drawn Nb nanowire-NiTi composite wires upon annealing were investigated. Nb nanowires in the composite wires exhibited strong <110> fiber texture and internal stress anisotropy, and the internal stress in the annealed composite wires gradually decreased as the annealing temperature increased above 500 °C, and Nb nanowires partly spheroidized into nanoparticles after annealed at 800 °C. Different temperatures annealed composite wires exhibited significantly different phase transformation behaviors, and NiTi matrix in these composites is in different phases at room temperature. With the increase of annealing temperature, the phase structure of the NiTi matrix underwent the evolution of oriented B19′ martensite, B2 parent phase, oriented R phase and self-accommodated B19′ martensite phase. Meanwhile, the reoriented textures of B19′ martensite and R phases are induced by the internal stress in NiTi matrix.