Heterogeneous precipitation of γ′′ along LAGBs during post-heat treatment of powder bed fusion additively manufactured IN718 superalloy

Abstract

Envelop of γ′′ precipitates is observed along low angle grain boundaries (LAGBs) after post-process heat treatment of IN718 produced through laser assisted powder bed fusion additive manufacturing technique (PBF-AM). Solutionization of as-built IN718 at 1030 °C for 1 hr resulted in a redistribution of elemental Nb in the γ matrix and the formation of low energy dislocation structure along LAGBs while retaining the as-build grain structure. Subsequently, double aging treatment resulted in heterogeneous precipitation of γ″ along LAGBs with homogeneous precipitation within the grains. Electron microscopy and 3D atom probe observations along with Calphad simulations were used to understand the microstructure at each stage to create the pathway leading to near complete utilization of Nb for γ″ formation while retaining the as-build structure.