Effect of solid solution elements on cracking susceptibility of Ni-based superalloys during additive manufacturing

Alloy composition design usually contributes to eliminating cracking in Ni-based superalloys during additive manufacturing (AM). However, a detailed understanding of each solid solution element in the cracking susceptibility of Ni-based superalloys during AM is still missing. Thirteen newly designed alloys are considered to investigate the combined effect of solid solution elements on cracking susceptibility. The behaviors of solidification cracking, liquation cracking, and solid-state cracking were analyzed by the microstructural characterization and thermodynamic calculations. The results showed that W and Mo cause the formation of high melting-point carbides at grain boundaries (GBs), which increase solidification cracking susceptibility. Moreover, W and Mo lead to a slightly higher solidification cracking index (SCI) compared to Co, Cr, and Re. In the successive solidification and remelting process, the borides enriched in W, Mo, and B around GBs will cause grain boundary segregation and liquation cracking. W and Re extend the freezing range (FR) and exacerbate the segregation of Al and Ti in the inter-dendritic regions, contributing to the formation of eutectics. Similarly, complete or partial melting of the eutectic can induce liquation cracking during the thermal cycling in AM. The solid-state cracking susceptibility can be reduced by solid solution elements, especially Re and Co. In summary, compared to Co, Cr, and Re, W and Mo exacerbate the cracking susceptibility.