Study on Cracking Mechanism of Laser Deposition Repaired Heterogeneous Nickel-Based High Temperature Alloy

In view of repair difficulty of the high crack sensitivity K424 nickel-based superalloy thin wall piece, the low crack sensitivity GH4169 nickel-based superalloy powder was employed in deposition repairing on K424 superalloy substrate.The characteristics of cracks and the mechanisms of cracking during this process were studied. The results show that during the repair process, cracks initially initiate in the heat-affected zone of the base material, subsequently extending towards both the depositional zone and the interior of the base material. These cracks exhibit a sinuous intergranular cracking pattern, displaying typical liquation crack morphology. Morphological and compositional analyses indicate that the liquid film on the grain boundaries primarily originates from the eutectic reactions of incomplete melting larger-sized γ' phases and γ phases under laser irradiation, resulting in the formation of the liquid film under thermal conditions. Additionally, low-melting-point phases such as carbides and borides melt and accumulate at high temperatures, promoting the formation of liquation films at elevated temperatures.The numerical model established with Simufact Welding software validates the stress and temperature fields during the repair process, revealing significant stress fields near the heat-affected zone as the driving force for crack formation. Therefore, in the heat affected zone, the formation of liquid film on the grain boundary and the existence of large stress provide conditions for the formation of liquation cracks.