Evaluating the Microstructures and Mechanical Properties of Dissimilar Metal Joints Between a New Cast Superalloy K4750 and Hastelloy X Alloy by Using Different Filler Materials

Two kinds of filler materials were used to join dissimilar alloys between a new cast superalloy K4750 and Hastelloy X by tungsten gas arc welding (GTAW). The segregation behavior, interfacial microstructure and mechanical properties of the dissimilar joints were evaluated. The results show that both filler materials can be used to obtain sound dissimilar joints successfully. Microstructural observation show that no obvious cracking is observed in the joints achieved by both filler materials. The segregation extent of various elements in Hastelloy X weld metal is more severe than that in the K4750 weld metal. No unmixed zones were observed at the interfaces. Transition areas with the chemical compositions various between the K4750 alloy and the Hastelloy X alloy were found at the joint interfaces. The maximum width of the transition area between the K4750 weld metal and Hastelloy X base metal is smaller than that between the Hastelloy X weld metal and K4750 base metal. The ultimate tensile strength and yield strength of the joints with Hastelloy X filler material are slightly higher than those with K4750 filler material, however, the K4750 filler material results in a higher total elongation and fusion zone microhardness than those with Hastelloy X filler material. Both dissimilar joints fractured with a ductile feature which exhibits tearing edges and dimples. Hastelloy X filler material is suggested to be more suitable for joining of K4750 superalloy and Hastelloy X dissimilar metals in terms of obtaining superior comprehensive mechanical properties.