Strength-plasticity transition mechanism after the solution treatment of GH3230 superalloy fabricated via laser powder bed fusion

Abstract

Owing to their unique microstructure, GH3230 superalloys prepared using laser powder bed fusion (LPBF) exhibit high strength but low ductility, which limits their functional performance in engine combustion chambers. In this study, the process parameters were optimized to obtain LPBF GH3230 with minimal defects, and solid-solution treatment (ST) was conducted to modulate its inhomogeneous microstructure and mechanical properties. The results revealed that ST eliminated the substructure of as-printed (AP) samples and transformed nano-M23C6 into micron and submicron M6C/M12C in situ. Significant amounts of M6C/M12C promoted Orowan strengthening, but the quasi-continuous semi-coherent lattice interface between M6C/M12C and the matrix was a weak zone for cracking, resulting in reduced plasticity owing to the presence of micron carbide. The increased solid solution temperature causes the carbide to remelt, triggering a strong plastic transformation. The impact of carbide size on strength and plasticity conversion rate was more significant than that of carbide content. Final, LPBF-GH3230 samples containing micron carbides were obtained in ST below 1230 °C with an ultimate tensile strength (UTS) comparable to that of forgings. Further increase in the ST temperature to 1280 °C eliminated the carbides, a LPBF-GH3230 that fulfilled the strength standard for cast parts (647 ± 23 MPa) with an excellent elongation (39.4 ± 1.7%) was obtained. This study provides a theoretical basis for the practical application of the LPBF GH3230 superalloy in the aerospace industry and offers guidance for improving post-treatment methods to ensure high plasticity.