The microstructural evolution of laser powder-bed additively manufactured Inconel 625 during a post-build stress-relief anneal of 1 hour at 1143 K (870°C) is investigated. It is found that this industry-recommended heat treatment promotes the formation of a significant fraction of the orthorhombic D0 a Ni 3 Nb d-phase. This phase is known to have a deleterious influence on fracture toughness, ductility, and other mechanical properties in conventional, wrought Inconel 625; and is generally considered detrimental to materials' performance in service. The d-phase platelets are found to precipitate within the inter-dendritic regions of the as-built solidification microstructure. These regions are enriched in solute elements, particularly Nb and Mo, due to the micro-segregation that occurs during solidification. The precipitation of d-phase at 1073 K (800°C) is found to require up to 4 hours. This indicates a potential alternative stress-relief processing window that mitigates d-phase formation in this alloy. Ultimately, a homogenization heat treatment is recommended for additively manufactured Inconel 625 because the increased susceptibility to d-phase precipitation increases the possibility for significant degradation of materials' properties in service.

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