Dissimilar welding of Hastelloy C-2000 and Monel 400 by Laser beam welding: Metallurgical and mechanical insights

This study investigates the dissimilar welding of Hastelloy C-2000 and Monel 400 using Laser Beam Welding (LBW). Owing to the differences in their chemical, thermal, and metallurgical characteristics, joining these alloys can lead to elemental segregation, undesirable phase formation, residual stresses, and reduced joint performance. Hence, a low-heat-input and precisely controllable process is required to minimize metallurgical degradation and thermal distortion. This study evaluates the metallurgical and mechanical characteristics of dissimilar joints to assess the suitability of LBW for high-performance alloy applications. Detailed microstructural analysis was performed using Optical Microscopy, Scanning Electron Microscopy, and X-ray Diffraction, revealing finer dendritic structures and minimal intermetallic phase formation. Residual stress measurements indicated lower tensile stress magnitudes in the LBW welds, which was attributed to the rapid thermal cycle and reduced heat input. Mechanical characterization through tensile, Charpy impact, and hardness testing showed that the LBW joints exhibited 12–15% higher ultimate tensile strength and up to 20% greater impact toughness. The hardness distribution across the weld zone was more uniform, indicating better metallurgical bonding and lower thermal distortion. Moreover, LBW resulted in a narrower heat-affected zone and reduced the weld bead width, thereby enhancing the joint quality. The key findings revealed that LBW produced high-aspect-ratio welds with narrow HAZs, refined dendritic microstructures, and minimal elemental segregation. XRD analysis confirmed a predominantly single-phase FCC Ni–Cu solid solution with minor carbide formation and no harmful intermetallic compounds. The fusion zone exhibited a hardness of approximately 244–251 HV, confirming the high mechanical integrity of the welded joint.