Designing nickel base alloys for microstructural stability through low γ-γ′ interfacial energy and lattice misfit

An extended stability alloy design strategy for multicomponent γ-γ′ nickel-base alloys with near-zero lattice misfit and as low as possible interfacial energy was investigated by isothermal annealing of two experimental alloys at 900°C for times up to 256h. The coarsening behavior of the spherical γ′ precipitates and the phase compositions determined by atom probe tomography were utilized to exploit a modified Lifshitz-Slyozov-Wagner relationship to estimate the interfacial energies. The estimated interfacial energies are much lower than predicted by a CALPHAD-based software as well as those typically reported for multicomponent γ-γ′ nickel alloys. Despite successfully minimizing the interfacial energy and γ-γ′ lattice misfit, these factors alone were not sufficient to impart high temperature extended stability through reduced coarsening kinetics.