Thermal Stability of the R Phase of a Rapidly Solidified Ti-47.3Ni (at%) Alloy

Transformation behavior of rapidly solidified Ti-47.3Ni (at%) alloy ribbons and thermal stability of the R phase in theribbons were investigated by means of differential scanning calorimetry (DSC), X-ray diffraction, and transmissionelectron microscopy. Rapidly solidified Ti-47.3Ni alloy ribbons showed the two-stage B2-R-B19' martensitictransformation behavior. The B2-R transformation in the ribbons was observed even after annealing at 1,223 K,which was attributed to the fact that a specific orientation relationship between Ti2Ni and matrix in the ribbons ismaintained after annealing at 1,223 K. The DSC peak temperature of the B2-R transformation (TR*) decreased withraising annealing temperature, which was attributed to the increased volume fraction of Ti2Ni, thus causing anincreased Ni content in the matrix.