Microstructure and mechanical properties at elevated temperatures of as-built and heat-treated Inconel 718 produced through laser powder bed fusion processes

Purpose This study aims to better understand the influence of various post-treatments on the microstructure and mechanical properties of additively manufactured parts for critical applications. Design/methodology/approach In this study, Laser Powder Bed Fusion (LPBF) fabricated Inconel 718 (IN718) samples were subjected to various heat treatments, namely homogenization, solution heat treatment and double aging, to investigate their influence on the microstructure, mechanical properties and fracture mechanism at an elevated temperature of 650 °C. Homogenization treatment was performed at 1080 °C for durations ranging from 1–8 h. The solution treatment temperature varied from 980 °C to 1140 °C for 1 h, followed by double aging treatment. Findings At 650 °C, the as-built sample showed the minimum strength but demonstrated the maximum elongation to failure compared to the heat-treated samples. The strength of the IN718 superalloy increased by 20.26% to 34.81%, while ductility significantly reduced by 65.26% to 72.89% after various heat treatments compared to the as-built state. This change is attributed to the enhancement in grain boundary strength resulting from the pinning effect of the intergranular δ-phase. Originality/value The study observed that the variations in the fracture mechanism of LPBF fabricated IN718 depend on the duration and temperature of heat treatment. This research provides a thorough overview of the high-temperature mechanical properties of LPBF fabricated IN718 subjected to different homogenization times and solution treatment temperatures, correlating these effects to the corresponding changes in microstructure.