Microstructure Evolution of Powder-Mixed Inconel718-xRene88DT Alloy Fabricated by Direct Laser Deposition

By regulating Inconel718-xRene88DT (x = 0–100%) alloy powder, microstructure evolution and microsegregation of as-deposited samples fabricated by direct energy deposition (DED) are investigated. The novelty of this approach lies in the systematic regulation of the alloy composition to study its impact on microstructure and microsegregation, which is an important prerequisite to improving the performance of DED superalloys. It is found that the as-deposited microstructure mainly consists of predominant γ columnar dendrites directionally growing along the deposition direction. With the increase of Rene88DT proportion, thelayered structure tends to be more obvious, and the amount and size of γ′ phase increases. The content of the Laves phase is in decline. As a result of the microsegregation, the needlelike δ (Ni₃Nb) and lath-shaped η (Ni₃Ti) precipitate in the interdendritic regions when the proportion of Rene88DT is above 60%. The various microstructures, microsegregation, and their correlations at different proportions of Rene88DT DED samples are discussed. The relationship between composition and microstructure evolution is investigated based on the alloying mechanism, which can guide alloy design and process optimization for enhanced properties in AM-built Ni-based superalloys.