Cracking mechanism of GH5188 alloy during laser powder bed fusion additive manufacturing

GH5188 cobalt-based superalloy components fabricated using laser powder bed fusion (LPBF) additive manufacturing technique possess promising application prospects in aviation industry, but high cracking susceptibility of the alloy remains an important concern. In this paper, cracking mechanism of the LPBFed GH5188 alloy was investigated by analyzing microstructure, fracture surfaces, composition distribution and grain boundary characteristics of the prepared sample. It was found that cracks consistently propagate intergranular at grain boundaries with high misorientation angle. The cracks were confirmed to be solidification cracks, due to the existence of fracture surface with dendritic morphology, as well as the absence of eutectic structure, carbide and precipitated phase. Lanthanum oxide particles were observed in the as-built alloy, which may hamper feeding of molten material at interdendritic region, promoting tearing of liquid films. Hence, it could be suggested that low O and La contents help in avoiding crack formation. This work could provide guidance for fabrication of crack-free LPBFed GH5188 alloy components.