Abstract
FSX-414 is a cobalt-based superalloy widely used in stationary gas turbine blades due to its high-temperature strength and oxidation resistance. However, service-induced degradation often necessitates repair welding to extend component life. In this study, the effect of filler metal selection on the microstructure and mechanical performance of GTAW-repaired FSX-414 was investigated. Four filler metals, namely FSX-414, HS25, HS188, and Mar-M918, were evaluated under identical welding conditions. The repaired joints were characterized using optical microscopy, SEM/EDS analysis, Vickers microhardness testing, and tensile testing conducted at both room and elevated temperatures. The results showed that filler metal composition significantly influenced dendritic morphology, carbide formation, hardness, and fracture behavior. The average weld metal hardness ranged from 367.5 HV for HS25 to 425 HV for HS188. Mar-M918 exhibited the best tensile performance, with the highest ultimate tensile strength and elongation, whereas FSX-414 showed the lowest values. Fractographic and microstructural observations indicated that variations in carbide precipitation and elemental segregation contributed to the observed mechanical behavior. Overall, Mar-M918 provided the most favorable strength–ductility balance, highlighting the critical role of filler metal selection in repair welding of FSX-414.