Segregation and crack formation in laser welded IN792 equiaxed superalloy

IN792 is a Ni-base superalloy commonly employed for manufacturing blades and rotors of jet engines owing to its excellent mechanical properties and corrosion resistance at high temperature. These components operate in a very hostile environment and are exposed to high temperature and stress which can lead to the formation of cracks compromising their performance. Laser welding is a suitable high-energy density method to repair the damaged parts; however, if the IN792 superalloy has a structure with equiaxed grains, new cracks may be caused by the welding process. SEM observations highlighted that the fracture surfaces exhibit the typical morphology of a brittle fracture. XPS investigations made on the crack surfaces showed that they are enriched of Co. Co segregation has been explained by considering the migration of alloying elements in the melt during solidification. In the final stage of solidification, the volume contraction of the last liquid, rich in Co and entrapped in the already solidified parts, is not compensated. This results in relevant stresses that can lead to crack nucleation. Crack propagation takes place in brittle mode due to the significant presence of oxides which represent a preferred pathway for crack advancement.