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 L1 2 structure as the most important local configuration. Neither the static nor the dynamic atomic displacements indicate any precursor of the stable hexagonal phase (D0 24 structure) containing 25 at.% Ti. Metastable states with precipitates showing non-stoichiometric L1 2 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.