Influence of Heat Treatments on Microstructures and Properties of GH80A Superalloy for Buckets of USC Steam Turbines

Abstract:

The microstructure evolution and property variation of GH80A superalloy after a series of solution heat treatments, single or double aging treatments and long time aging at 550~750 °C for 10 000 h were investigated. Results show that the precipitation temperature of γ′ precipitates is identified as 930~950 °C. The γ′ precipitation could be inhibited by water quenching and cooling medium shows more effects on cooling γ′ precipitate than the solution temperature. Primary γ′ precipitates are strongly influenced by aging temperature and the precipitation of secondary γ′ precipitates just begins at double aging stage. The tensile strength after single/double aging is decreased a little with the solution temperature increasing while the plasticity is increased. Long-time aging microstructure shows good stability below 700 °C and the coarsening of primary γ′ precipitates proceeds by volume diffusion below 700 °C while by interface controlling at 750 °C