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Characterization of microstructure and mechanical properties of nickel based superalloy 617 by pulsed current gas tungsten arc welding technique

Nickel based superalloy (alloy 617) exhibits high strength and oxidation resistance at elevated temperatures. The major limitation of this alloy is microsegregation of alloying elements due to the formation of Molybdenum (Mo) rich secondary phases in the interdendritic region of the weldments. The present study investigates the possibilities to mitigate the microsegregation effect. In order to achieve this, weld joints were fabricated with pulsed current gas tungsten arc welding (PCGTAW) techniques with three different filler wires. The filler wires employed with present study are ERNiCrMo-4, ERNiCrMo-10 and ERNiCrMo-14. The macro examination was carried out to reveal the defects in the weld joints. Optical and Scanning electron microscope (SEM) analysis were performed to evaluate the micro structural changes in the fusion zone and Heat Affected Zone (HAZ). Microstructure shows the fine equiaxed dendrite structure in the fusion zone. Energy Dispersive x-ray Spectroscopy (EDS) analysis was also carried out in the weldments to quantify the level of microsegregation of alloying elements. Tensile test reveals the strength and ductility of the weld joints. Root and face bend test was carried out to check the ability of the weld joints to withstand bending forces. The result shows the defect free weld was achieved in all the welded joints. EDS analysis revealed the presence of Mo rich phases in the ERNiCrMo-4 filler wire. There is no evidence for the formation of secondary phases in the filler wires. The tensile strength of ERNiCrMo-14 filler shows the marginally higher strength compare to other filler wires. Root and Face bend test did not show the presence of cracks and other defects in the weldments.