Effect of remelting on cracking of Inconel 939 fabricated via laser powder bed fusion

Laser remelting of each layer during laser powder bed fusion (L-PBF) is an important strategy used for enhancing the quality of components. However, the impact of remelting on internal cracking has not been completely understood. This study investigates the feasibility of employing remelting to mitigate internal cracking using Inconel 939 (IN939) as an example, a high-temperature nickel-based alloy with high susceptibility to cracking during L-PBF. The effects of remelting parameters, strategies, and the number of remelting cycles on microstructure features and defects were studied. The residual stresses in remelted samples and initial melt samples were measured for different laser scanning strategies. Reduction in residual stresses is identified as a key factor in minimizing cracking, with the lowest residual stresses observed in remelted samples using the chess strategy. Additionally, crack density in remelted samples was decreased with reducing cellular dendrite size in the fabricated sample. In comparison to initial melt samples, remelted samples exhibited an 85% reduction in crack density and a 60% reduction in porosity. These findings present a potential approach for defect inhibition during L-PBF processing of IN939 and other high-temperature alloys.