Strong Impact of Minor Elements on the Microstructural Evolution of an Additively Manufactured Inconel 625 Alloy

Inconel 625, whereas designed as a single-phase solid-solution-strengthened alloy, is prone to formation of various precipitate phases under processing or service conditions. When this alloy is fabricated with additive manufacturing, the enhanced segregation of alloying elements to grain boundaries, interdendritic regions, or dislocation cores can influence microstructural evolution and modify local precipitation pathways. In this study, an Inconel 625 made with laser powder-bed fusion is characterized with comprehensive electron microscopy techniques combined with thermodynamic calculations, with emphasis on element segregation, precipitate formation, and their relation to the columnar sub-grains associated with additive manufacturing. Enrichment of both major (Nb, Mo) and minor (Si, N) solutes at dislocation cell walls is observed in the as-built samples, whereas stress-relief heat treatments promote formation of two types of globular precipitates, i.e., (Nb, Mo, Si, N)-rich M 6 X and (Nb, N)-rich MX. Absence of the detrimental, needle- or plate-shaped δ -Ni 3 (Nb, Mo) phase leads to improved mechanical properties and is attributed to the higher concentrations of Si and N at cell walls, although the overall composition remains within the standard range for powder-bed fused alloys. These new insights into the critical role of minor alloying elements provide a potent guide for the design and processing of additively manufactured metallic materials.