Gas turbine blades made from nickel-based superalloys, valued for their high temperature stability and creep resistance, undergo various forms of microstructural degradation during extended service at elevated temperatures that can ultimately lead to blade failure. To extend blade and turbine rotor life, Sulzer has developed evaluation and rejuvenation processes that include microstructural assessment and stress rupture testing of specimens from service-exposed blades. While stress rupture testing presents certain limitations and challenges in evaluating material condition, Sulzer has successfully rejuvenated hundreds of gas turbine blade sets across multiple superalloy types, including GTD 111, IN 738 LC, and U 500, demonstrating the effectiveness of heat treatment rejuvenation in improving microstructure and mechanical properties of service-degraded components.

The A286 is one of the earliest superalloys developed. It has been used for manufacturing different components of turbo machineries because of its balanced high temperature properties. These components include shafts, discs, spacers, blades and fasteners. This paper reviews some of the issues and recent field experiences related to metallurgy, fabrication, in-service evaluation and failure of some of these components. The fabrication aspects including the effects of alloy melting processes, forging parameters and different types of heat treatments on the processed parts are discussed. The importance of these factors on the microstructure and properties of A286 are highlighted. The effects of service exposure on some of these parts are also discussed. In service evaluation involves checking for service induced damage or changes in microstructures and properties so that the suitability of the part for continued service can be determined. The failure analysis section of the paper briefly discusses failures of two expander wheels and an expander disc made out of A286 to pinpoint some of the salient features of damage accumulation and fracture during service.