In-situ neutron scattering studies of order and decomposition in Ni-rich Ni–Ti

Diffuse wide-angle neutron scattering experiments have been performed for two states of thermal equilibrium within the γ solid solution, 58Ni–5.8 at.% Ti at 777 K and 58Ni–9.6 at.% Ti at 1103 K. The analysis of the Clapp configurations yields the basic cluster of the L12 structure as the most important local configuration. Neither the static nor the dynamic atomic displacements indicate any precursor of the stable hexagonal phase (D024 structure) containing 25 at.% Ti. Metastable states with precipitates showing non-stoichiometric L12 structure evolve during the decomposition of supersaturated Ni–11.3 at.% Ti polycrystals as seen by in-situ small-angle neutron scattering. From the integrated small-angle scattering intensity, the Ti content of the cuboidally shaped precipitates in the metastable γ′′ state is found to be about 17 at.% between 870 and 950 K.