LAUSR

Abstract Rietveld refinement of neutron diffraction patterns obtained in-situ during the reactive sintering of Ni-Ti (49 at% Ni: 51 at% Ti) elemental powder compacts for two sintering profiles was performed. The atomic displacement parameter ( U is o ) for each phase that occurs during reactive sintering (α-Ti, β-Ti(Ni), Ti 2 Ni(O), NiTi, Ni 3 Ti and Ni) were obtained from separate in-situ experiments. The phase fractions determined from the two sintering runs were found to be in excellent agreement, with an uncertainty estimated at ± 1.6 wt%. Intermetallic phases do not begin to form until 600 °C. Initially, Ti 2 Ni(O) grows faster than NiTi and Ni 3 Ti. By 780 °C, NiTi becomes the dominant phase, growing at the expense of all the other phases. Homogenization occurs at 1100 °C and the microstructure consists of 93 wt% NiTi and 7 wt% Ti 2 Ni(O). Experimental evidence along with the refinement of the O concentration in Ti 2 Ni(O) during sintering was used to explain the persistence of Ti 2 Ni(O) in the microstructure. The oxygen raises the melting point of the phase such that it is in equilibrium with NiTi at 1200 °C, despite Ti 2 Ni having a melting temperature of 984 °C.