Low heat input welding of nickel superalloy GTD-111 with Inconel 625 filler metal

GTD-111 precipitation-strengthened nickel-based superalloy is widely used in blades of gas turbine engines which operate at high temperature and in a hot localized corrosion atmosphere. After long-term exposure to high temperature, gamma' precipitate is known to exhibit catastrophic changes in size and distribution which cause deterioration of its properties and failure of the component. In this study, a damaged blade removed froma land-based gas turbine generator was subjected to nonpre-heat-treated GTAW and laser welding repair with various welding powers in the range of 135 to 295 J x mm(-1), followed by post-weld heat treatment (PWHT) at 1473 K for 7200 s and strain aging at 1118 K for 86 400 s. Results show no significant relationship between welding powers, size and area fraction of the gamma' precipitate in the fcc gamma matrix in both GTAW and laser-welded specimens. The final gamma' precipitate size and distribution depend mainly on PWHT parameters as gamma' precipitates in all GTAW and laser welded specimens showed similar size and area fraction independently of the heat input from welding. Unmixed zones are observed in all laser welding specimens which may cause preferential weld corrosion during service. Microcrack occurrence due to welding and PWHT processes is also discussed.