Keyhole gas tungsten arc welding (GTAW) is a promising welding technique that enhances productivity and sustainability in the manufacturing industry. The substantial heat input associated with the single-pass keyhole-GTAW influences the phase transformations occurring in the weld. This study aims to investigate the microstructural evolution during keyhole-GTAW of the IN617 nickel-based superalloy. The microstructure of the fusion zone exhibits large columnar grains and a coarse dendritic solidification structure, accompanied by interdendritic micro-segregation which lead to the formation of titanium-rich M(C,N) and molybdenum-rich carbides. The heat-affected zone is characterised by the dissolution of carbide stringers. Notably, no constitutional liquation was observed. The implications of solidification and solid-state phase transformations on the hardness characteristics and tensile properties of the weld are discussed.
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