Preprint - Heat Treatment and Stress-Relief Optimisation of Laser Powder Bed Fusion Inconel 939 for High-Temperature Applications

Preprint for publication: heat treatment and stress-relief optimisation of Laser Powder Bed Fusion Inconel 939 for high-temperature applications. Inconel 939 (IN939) is a valuable material in the aerospace industry because of its retention of mechanical properties at elevated temperatures. Components fabricated by laser powder bed fusion (PBF-LB) can benefit from the design freedom and near-net shape, enabling topology-optimised or organic bio-inspired shapes that enhance performance while reducing material waste. However, the aerospace sector demands high part quality and process stability, requiring well-defined fabrication and post-processing to avoid defects and ensure consistent results. Therefore, this study investigates the fabrication of IN939 PBF-LB and evaluates the effects of different stress-relief annealing and heat treatment conditions to improve creep performance. Stress-relief annealing was performed at 760 °C, 860 °C, and 960 °C. The optimal temperature of 860 °C minimised the deformation of the cantilever without undesirable phase formation. In addition, three different heat treatment routes were applied, resulting in notable differences in microstructure, tensile strength, and creep resistance. The heat treatment that produced the longest creep rupture life at 870 °C and 100 MPa achieved 48.33 hours, with an ultimate tensile strength of 1439 MPa, 13.7% elongation at break, and hardness of 448 HV0.3. Further opportunities for enhancing creep resistance through heat treatment design are also discussed. These findings offer valuable quantitative insights into how heat treatment conditions influence microstructure and performance of additively manufactured IN939, thereby guiding the optimisation of post-processing strategies for advanced, bio-inspired high-temperature components.