Transformation behaviour of Ti–Ni and Ti–Ni–Cu alloy ribbons with nano Ti2Ni particles

Ti–Ni and Ti–Ni–Cu alloy ribbons have been prepared by single roll melt spinning, and then martensitic transformation behaviours were investigated by means of transmission electron microscopy, differential scanning calorimetry and X-ray diffraction. In 51Ti–49Ni(at.%) alloy ribbons, Ti2Ni particles of a size less than 50 nm with the coherent interface with the matrix were found, while they were not found in 50Ti–50Ni alloy ribbons. In 49Ti–46Ni–5Cu and 50Ti–45Ni–5Cu alloy ribbons, Ti2Ni particles of size less than 30 nm with coherent interface with the matrix were found. Coherent Ti2Ni particles induced the R phase transformation in Ti–Ni alloys, and consequently transformation occurred in two-stages, i.e., B2–R–B19. Coherent Ti2Ni particles induced the B19 martensite in a Ti–45Ni–5Cu alloy, and consequently transformation occurred in two-stages, i.e., B2–B19–B19′. The change in transformation behaviour was ascribed to strain fields developed around coherent Ti2Ni particles.