Temperature dependence of lattice parameter, misfit and thermal expansion coefficient of matrix, γ′ phase and superalloy

In order to determine the temperature dependence of the misfit of the nickel-based superalloy CMSX-4, the lattice parameters of its constituents, gamma' phase and a nickel solid solution, have been determined by neutron diffraction measurements and compared with the lattice parameters of the two-phase superalloy of earlier experiments. From these data, the thermal expansion coefficients and the unconstrained misfit is calculated. As a second method, the macroscopic volume change was determined by dilatometer measurements and compared with that of the neutron scattering experiments. It can be concluded that both, the differences in macroscopic thermal expansion as well as the concentration changes between the phases, are able to explain the slightly increasing more negative misfit of the superalloy for temperatures up to 1100 K, whereas at even higher temperatures concentration shifts are solely responsible for the misfit changes.