On the deformation induced heterogeneous precipitation of γ″ phase in Inconel 718 alloy

Abstract

The unique coherency strain hardening mechanism and sluggish precipitation kinetics of γ″ phase have enabled Inconel 718 excellent elevated temperature serving performance and formability. However, the orienting character of γ″ phase determines its precipitation mutability and its morphology is susceptible to external stress and plastic deformation. Inconel 718 alloy is generally fabricated through plastic processing technologies like forging and rolling, where heterogeneous γ″ particles are commonly observed after aging. Therefore, it is vital to reveal the structural factor inducing the heterogeneous γ″ precipitation caused by deformation to lay fundamentals for particle configuration control. For this purpose, the present work aimed to define the heterogeneous γ″ configuration induced by prior deformation and explore the relevant structural mechanism. The γ″ particle morphologies in directly-aged cold-rolled Inconel 718 were characterized, prior rolling deformation resulted in heterogeneous γ″ precipitation during the aging process, which was defined as the inequivalence in their relative number fraction and particle size of perpendicular γ″-variants. Deformation led to the formation of β grains with lattice distortion in Inconel 718 alloy, which was the primary structural factor to induce the heterogeneous γ″ precipitation. These results explained that the FCC-γ lattice distortions caused by plastic deformation were responsible for the heterogeneous precipitation of second-particles.