In-situ synchrotron HEXRD study on the stress relaxation behavior and internal stress evolution mechanism of a PM nickel-base superalloy

Abstract

FGH96 is a powder metallurgy nickel-base superalloy used for turbine disk of aero-engines. In this study, the evolution of micro-lattice stress and strain of FGH96 alloy during stress relaxation and thermal deformation was investigated by employing in-situ high-energy synchrotron radiation techniques. Results indicate that the relaxation of macroscopic compressive stress is closely related to the increased lattice strain in grains of different orientations. During high-temperature relaxation, the lattice stress of the (111)γ/γ′ and (220)γ/γ′ planes decreases rapidly in the initial relaxation phase and then stabilizes, while the lattice stress of the (200)γ/γ′ plane remain uniformly relaxed throughout, suggesting minimal load transfer between different grains. During the high-temperature compression and holding process, dynamic recrystallization partially releases the internal stress generated by work hardening. During the holding stage, different stress relaxation mechanisms were observed for grains of varying orientations, with (311) oriented grains primarily achieving this through dislocation rearrangement and sub-grain nucleation, while (220) oriented grains tend to migrate grain boundaries based on existing recrystallization nucleation.