On the oxygen-induced hot cracking in a direct laser deposited Ni-based superalloy

We report on the observation of a novel hot cracking mechanism in a direct laser deposited nickel-based superalloy, using joint electron, X-ray, and atom microscopy. The majority of the observed cracks were related to Ni and Mo oxides formed in grain interiors as well as at grain boundaries. Using atom probe tomography, we detected an intermediate zone between oxide particles and the base alloy, where oxygen existed in solid solution and chemical compositions varied due to the oxide formation. The variation in composition lowered the melting point of the matrix while the oxides promoted stress concentration and crack nucleation, thus causing liquation cracking during reheating.