Paper Title
Investigation of Monel 400 to Inconel 718 Dissimilar Alloy GTA and EB Welds

Abstract - Ni-based alloy such as Monel 400 and Inconel 718 is used in gas storage pressure vessels of human space launch vehicles because of its high strength and excellent resistance against oxidation and corrosion. The need for dissimilar joining arises at the components of the two dissimilar materials are assembled together. In this paper, the weldability, mechanical and metallurgical characteristics of Monel 400 to Inconel 718 dissimilar alloy gas tungsten arc (GTA) and electron beam (EB) welds are studied. The effect of the welding processes on microstructure, tensile properties and hardness were investigated. Further effects of filler wire (Inconel 718 and ERNiCu-7) on the tensile properties, location of failure, mode of failure and microstructure evolution of dissimilar welds were studied. For comparison, the similar alloy welds of Inconel 718 and Monel 400 were made and studied. Results showed that the heat input of the process influences the microstructure evolution and mechanical properties. With the GTA and EB weld parameters used, welds do not show any solidification cracking or HAZ liquation cracking. High energy beam welds (EBW) showed superior properties and a finer-grained microstructure than the GTA welds in the dissimilar welds. The filler wires Inconel 718 and ERNiCu-7 show comparable tensile properties, and the location of failure was observed in the Monel 400 base material. However, a hardness survey across the weld showed higher hardness in the fusion zone of Inconel 718 filler welds than ERNiCu-7. Similarly, for EBW location of failure for dissimilar welds was observed in the Monel 400 base material. The fractograph shows a fully ductile mode of failure in the tensile test. The tensile properties of similar and dissimilar welds were corroborated with the hardness data across the welds. In the dissimilar welds of GTA and EB, higher hardness was achieved at the fusion zone than the Monel 400 base metal. Keywords - Monel 400, Inconel 718, Gas Tungsten Arc Welding, Electron Beam Welding, Dissimilar Welds.