As-Built Microsegregation and JMatPro Analysis in Laser Powder Bed-Fused Inconel 718

Laser powder bed fusion enables the fabrication of complex Inconel 718 components, but rapid solidification produces pronounced microsegregation that complicates subsequent phase evolution. In this study, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy were combined with JMatPro calculations to examine as-built microsegregation and phase behavior in laser powder bed-fused Inconel 718. The as-built alloy exhibited a continuous cellular and dendritic substructure, a high dislocation density, and interdendritic constituents with pronounced Nb enrichment and weaker local Mo enrichment. Equilibrium calculations based on the measured powder composition predicted γ formation at approximately 1350 °C and a liquid plus γ region between 1195 and 1350 °C. The calculated stability ranges of MC, δ, η, γ′, σ, M23C6, Laves, and μ phases were also identified. Comparison with the experimental observations showed that calculations using the nominal composition cannot directly represent the strongly segregated interdendritic regions formed during rapid solidification. The TTT and CCT calculations indicated that δ phase precipitation is most sensitive at approximately 900 to 1000 °C. The results clarify the distinction between local nonequilibrium phase formation and bulk phase stability and highlight the role of Nb redistribution among interdendritic constituents, the δ phase, and γ″ and γ′ precipitates. The calculated results should be regarded as a qualitative reference. Further local composition-based calculations and experimental validation are required before they can be applied to heat treatment design.