In situ structural and texture analyses of monoclinic phase for polycrystalline Ni-rich Ti49.86Ni50.14 alloy from neutron diffraction data

Abstract

Phase transformation temperatures of a polycrystalline Ni-rich Ti_49.86Ni_50.14 shape memory alloy were investigated using a differential scanning calorimeter. In situ structural and texture analyses of the monoclinic Ti_49.86Ni_50.14 were investigated using neutron powder diffractometer technique. Differential scanning calorimeter results showed that this Ni-rich alloy has a one-step cubic to monoclinic martensitic phase transformation on cooling and a one-step monoclinic to cubic transformation on heating. In situ high-resolution neutron powder diffraction data of the monoclinic phase from low temperatures to room temperature on heating are consistent with the differential scanning calorimeter’s heating results. In addition, the refined monoclinic crystal structure parameters for all neutron diffraction data sets agree satisfactorily with single-crystal X-ray diffraction results. The multiple-data-set capabilities of the GSAS Rietveld refinement program, with a generalized spherical-harmonics description was used successfully to extract the texture description directly from a simultaneous refinement using 52 time-of-flight monoclinic neutron diffraction patterns, taken from a polycrystalline sample held in 13 orientations inside the diffractometer.