Investigating the Effects of Repair Welding on Microstructure, Mechanical Properties, and Corrosion Behavior of IN-939 Superalloy

This study aimed to investigate the effects of tungsten inert gas (TIG) repair welding on microstructure, mechanical properties, and corrosion resistance of Inconel 939. After welding with Inconel 625 filler under argon atmosphere, the microstructure, hardness, tensile strength, and corrosion resistance of the specimens were analyzed. The results showed that the hardness value and corrosion resistance decreased in the heat-affected zone and particularly in the fusion zone. These changes were attributed to a decrease in the amount of γ’ phase in the fusion zone, the generation of liquation cracking, and the accumulation of dislocations. Also, the cyclic hot corrosion tests were conducted on the specimens prepared from the base metal and the weldment in a synthetic molten salt environment for 30 h at 900 °C, which corresponds to the operating temperature. The results showed that although the weldment remained unchanged by the end of the test, in contrast, the base metal began to change after initial cycles, and a brittle oxide layer formed on the surface. Finally, the results of hot tensile tests performed at 900 °C showed that TIG welding has limited effects on yield strength and elongation. Welding reduced the yield strength and elongation as much as 4 and 47%, respectively, of those of the BM.