Precipitation of δ phase in Inconel 718 superalloy: The role of grain boundary and plastic deformation

Abstract

The control of δ precipitations is important during the thermal processing of Inconel 718 superalloy (IN718) because it can control the grain size and affect the mechanical properties of the material. The main purpose of this study was the effects of plastic deformation and Grain Boundary Misorientation (GBMO) on δ phase precipitation at grain boundaries (GBs). The content of the δ phase and the number of precipitated orientations at the GB were statistically analyzed. It was found that the δ phase grew into grains along the {111} plane of γ-matrix after nucleation at the GB. Plastic deformation can change the morphology and precipitate location of δ phase, with the increasing of plastic strain, the content of the δ phase and the number of precipitated orientations in GBs increased, which was related to the piling up of dislocations caused by deformation and the slip of {111} plane. For the undeformed samples, the δ phase precipitation at the GB was affected by the GBMO, which was consistent with the change of GBs energy with the GBMO. The influence of the structure and characteristics of the interfaces (GBs and twin boundaries) on the precipitation behavior of the δ phase is also analyzed in this study.