Investigation on the Hot Crack Sensitivity of a Nickel-Based Single Crystal Superalloy Fabricated by Epitaxial Laser Metal Forming

In this study, the epitaxial laser metal forming(E-LMF) process was used to deposit a nickel-based single crystal superalloy under different cooling conditions, and its microstructure and formation mechanism were investigated. The results reveal that an epitaxial microstructure with an almost crack-free is formed under air-cooling, while water-cooling increases the hot crack sensitivity of the deposited due to the thermal stress accumulation. In the case of water-cooling, almost all cracks arise in the overlap zone, with a few cracks appearing in other regions. The element distribution analysis and grain boundary angle analysis show that micro-segregation, as well as high angle grain boundaries, result in typical solidification cracks. In the case of air-cooling, the crystal orientation of the deposited zone is consistent with that of the substrate, although there are some stray grains in the top zone. As the bottom layers are annealed for a longer time than the upper layers, the γ' phase is precipitated more at the bottom than at the top.