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 5]Ti-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-5ONi 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. (c) 2006 Elsevier B.V. All rights reserved.