Investigation of dissolution behavior of laves phase in inconel 718 fabricated by laser directed energy deposition

The mechanical properties of Inconel 718 are closely related to the morphology and size of the Laves phase, which must be quantitatively controlled to change the effect of the Laves phase from deleterious to beneficial. In this study, post-heat treatment was used to regulate the morphology and size of the Laves phase in Inconel 718 fabricated using laser directed energy deposition, and the dissolution behavior of the Laves phase during solution heat treatment was investigated. The results indicated that the sharp corners and grooves of the Laves phase preferentially dissolved, causing the morphology of the Laves phase to change from a long-striped to granular shape during dissolution. The dissolution kinetics of the Laves phase were also investigated using the Johnson–Mehl–Avrami–Kolmogorov and Singh–Flemings models. The initial stage of dissolution was controlled by both the long-range diffusion of Nb and the interfacial reaction. However, with decreasing degree of Nb segregation, the interfacial reaction became dominant.