Structural characterisation of melt-spun Ti50Ni25Cu25 ribbons

Abstract

The structure of melt-spun Ti 50 Ni 25 Cu 25 ribbons after various heat treatments has been studied by X-ray and TEM analyses. As-received amorphous Ti 50 Ni 25 Cu 25 ribbons, when annealed at 500°C for a few minutes, crystallise into the B2 structure, which fully transforms into the orthorhombic martensite upon cooling. The X-ray scans of Ti 50 Ni 25 Cu 25 ribbons annealed for 5 min. at 500°C show the well developed orthorhombic pattern, which was used for refinement of the orthorhombic martensitic structure of TiNi-Cu alloys. The refined structure of the orthorhombic martensite in TiNi-Cu alloys differs from the standard B19 type suggested previously. X-ray investigation reveals a shift of atoms in the (010) ORT layers from the centro-symmetric positions towards the [001] ORT direction. The longer annealing of Ti 50 Ni 25 Cu 25 ribbons at 500C causes TiCu precipitation and results in appearance of untransformed B2 grains at room temperature. Annealing at 700C causes Ti 3 Cu 4 precipitation with significant Cu depletion of the matrix resulting in the appearance of the mixed orthorhombic and monoclinic martensite.