Synergistic control of solidification cracks and MC carbides to enhance the tensile strength of electron beam welded GH4251 alloy joints

With the continuous advancement of the aviation industry, the demand for high-temperature alloys in aircraft engines has been increasing significantly. However, in the fusion welding of precipitation-strengthened nickel-based alloys with high Al and Ti content, crack formation and the precipitation of brittle phases remain major challenges that severely affect welding quality. This study investigates the fundamental principles governing the weldability and mechanical behavior of such alloys, focusing on the GH4251 alloy welded by electron beam technology. By optimizing the welding parameters, synergistic control of MC carbides and solidification cracks was successfully achieved, resulting in a room-temperature tensile strength of 1471 MPa — equivalent to 92 % of the base metal. Experimental and simulation results reveal that solidification cracks and MC carbides within the weld seam act as stress concentration sites under external loading, thereby accelerating macroscopic fracture of the joint. The occurrence of solidification cracks is further promoted by instantaneous tensile stresses and high-angle grain boundaries during welding. Moreover, a high density of dislocations was observed at the semi-coherent interface between MC carbides and the γ matrix, accompanied by pronounced tensile strain within the carbides themselves. Overall, this research provides new insights into the relationships among welding parameters, microstructural evolution, and room-temperature tensile strength in high Al and Ti precipitation-strengthened nickel-based superalloy joints.