Insights into the application of flat-top laser in selective laser melting processed Inconel 738 : simulation of solid-state phase transformation

This work proposes a novel thermal-metallurgical model (TMM) that integrates the flat-top laser (FTL) heat source model with the non-isothermal Johnson–Mehl–Avrami (JMA) phase transformation model. The TMM can predict the phase composition of selective FTL melting (SFLM) high-performance superalloys from the mesoscale, providing insights for customized component properties. We apply the TMM to quantitatively predict the solid-state phase transformation behavior (SPTB) and final phase distribution in a three-layer, two-track SFLM process of IN738 superalloy. Additionally, we investigate the dependency of SPTB on process parameters. The results indicate that during the printing process, based on the relative sizes of the peak temperature and phase transformation temperature ranges during material cyclic heating, the precipitation of γ′ phase can be divided into precipitation-dissolution stage, precipitation stage, and stable stage, with the precipitation phase exhibiting a non-uniform distribution after the printing. Regarding laser power, scanning speed, and substrate preheating temperature, the substrate preheating temperature parameter significantly impacts the average volume fraction of γ′ phases (AVFG). When the substrate preheating temperature changes from 200 to 600 °C, the AVFG increases from 3.480 × 10⁻¹⁰ to 2.724 × 10⁻⁵. The FTL heat source model within the TMM was validated with data reported in the literature. © The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2024.