Cooperatively controlling γ′ phase and M23C6 of a polycrystalline Ni3Al-based superalloy: Microstructure and creep resistance

Abstract

The intra-granular γ′ phase and inter-granular M₂₃C₆ in a polycrystalline Ni₃Al-based superalloy are cooperatively controlled through a two-stage-cooling solution treatment. The rapid cooling stage suppresses the coarsening of the γ′ phase, while the subsequent slow cooling stage promotes the precipitation of M₂₃C₆. The co-strengthening of intra- and inter-granular particles leads to a longer creep life. Intra-granularly, topologically inverse microstructures are formed, the deformation is dominated by the motion of antiphase boundary coupled superpartials. Inter-granularly, the movement of superdislocations towards the grain boundary is obstructed by the M₂₃C₆. Based on these observations, theoretical models are employed to construct the relationship between the creep properties and the micro/sub-structures. The threshold stress against dislocation movement contributed by γ′ phase, the boundary obstacle stress induced by M₂₃C₆ and the energy barrier for inter-granular cavity nucleation are calculated for discussion.