| Abstract Scope |
Laser powder bed fusion (LPBF) can produce gamma prime-strengthened IN738LC superalloys for critical aerospace applications, but the heat-treated microstructure is inferior to the conventional. Rapid thermal cycling in LPBF inhibits the formation of large gamma/gamma prime eutectics, blocky gamma prime precipitates, and lower carbides, resulting in different microstructure responses. While prior research focused on modifying the heat-treating temperatures and durations, the effects from heat-treating rates were not studied. Heat-treating rates are crucial since the final gamma prime distribution and morphology are influenced by initial supersaturation and precipitation states. This study investigated various heating and cooling rates at different heat treatment steps. SEM, TEM, and machine learning-assisted analysis were employed to examine phase morphologies and fractions. Microstructural studies and hardness revealed that conventional heat-treating rates may cause overaging in LPBF IN738LC. The findings reflect the importance of considering heat treatment rate for LPBF alloys, particularly those strengthened by secondary phase precipitations. |