Abstract:Different thermal exposure aging treatments were performed on DD6 nickel-based single crystal superalloy to obtain different degraded microstructures. The mechanism of microstructural degradation evolution, and corresponding residual strength and fracture mechanism were studied. Parametric characterization methods of microstructural degradation degree were explored, and a quantitative mapping relationship between residual strength and microstructural degradation degree was established. The results indicate that during thermal exposure aging process, γ′ phase undergoes dissolution or growth according to Ostwald ripening mechanism. After aging at 980 ℃ for 1190 h and 1100 ℃ for 100 h, the content of γ′ phase almost reaches thermal equilibrium state. With the increase in temperature and time, the width of γ and γ′ phases will continue to coarsen and gradually stabilize. Finally, the width of γ phase is about 400 nm and the width of γ′ phase is about 760 nm. While coarsening, DD6 alloy undergoes rafting under the internal γ/γ′ phase mismatch stress or applied loads. Coarsening and rafting both reduce the strength of DD6 alloy. Considering the effects of coarsening and rafting, the microstructure size parameter ωλ2 is used to establish a good quantitative mapping relationship with residual strength, and this characterization method for microstructural degradation does not depend on microstructure size in the initial state.