A new technology for repair welding of poorly weldable superalloy parts

Superalloys, which are designed to achieve excellent high-temperature resistance, normally contain a relatively high concentration of precipitation-strengthening elements (such as Al and Ti) and refractory elements, leading to poor weldability, including that of K423A alloy. In this study, fully environmentally protected tungsten inert gas (FEP-TIG) welding technology is proposed and employed for K432A castings repairing. Three different welding currents are applied to repair the parts, and all weld points are free of defects, exhibiting the excellent process tolerance of FEP-TIG. The microstructure of weld points is systematically evaluated by advanced electron microscopy. Various dendrite morphologies in the mixed zone (MZ) influenced by welding current and solidification conditions are revealed. The annealing treatment after welding induces the precipitation of Ni 3 (Al, Ti) γ′ phase in the MZ and M 23 C 6 carbide in the base metal (BM), affecting the microhardness of both zones. This study provides a valuable technology for repair welding of poorly weldable superalloy and establishes a theory foundation for further research of K423A repair welding.