LAUSR

Abstract The evolution of both microstructure and microhardness of the IN 740H alloy welding joint following 10,000 h thermal exposure at 750 °C was studied. In this study, the IN 617 filler metal was used to obtain the welding joint through the gas tungsten arc welding process without welding defects. The grain growth occurred in the heat affected zone (HAZ), epitaxial growth of the grains near the fusion line was observed, and the partition coefficients were calculated in the weld metal zone. The microhardness of the heat affected zone of the weld was slightly higher, compared to both base and weld metals. Following the solution treatment, recrystallization and further grain growth occurred in the weld zone, and the new equiaxed grains were formed. Following 10,000 h thermal exposure at service temperature (750 °C) without post weld heat treatment, the microhardness of the HAZ and the weld metal increased, as the exposure time was increasing; the interstitial element (C) was fully homogenized in the weld metal zone. The IN 617 filler metal can be a potential candidate material for the welding of the IN 740H alloy.