The Effect of a Laser-Based Heat Treatment on the Microstructure of a Superalloy After a Minimally Invasive Repair by Direct Energy Deposition

In this study, a laser-based heat treatment is applied on IN718 superalloy substrate repaired by a minimally invasive direct energy deposition process. The focus is on the laser-based heat-treated microstructure, aiming to enable minimally invasive repair processes to take place either "on-wing" or "near-wing". Hardness measurements were performed on the as-repaired and heat-treated microstructure, while electron microscopy, electron backscatter diffraction and atom probe tomography analyses were performed to investigate the microstructure. After the laser-based heat treatment, the hardness of the repaired part increased compared to the as-repaired and reached values similar to that of the substrate. Besides, microstructural analysis unveiled non-uniform γ″ precipitate formation, linked to observed micro-segregation from the repair process persisting post-heat treatment. Precipitation-free areas were observed while co-precipitation of γ″ and γ′ in duplet and triplet particles was infrequent. Interdendritic areas exhibited Laves phases regions with needle-shaped δ precipitates forming directly from the Laves phase. Carbonitrides coexisted with Laves phase, creating complex Laves regions. Although a single-step heat treatment will not lead to a complete dissolution of the undesirable microstructure features, a solution treatment step using the same minimally invasive equipment can unlock the full potential of in-situ maintenance through laser-based heat treatments.