关键词: GH4169合金, 高温时效, γ″→δ相相变, 析出相演化, 析出强化, 屈服强度模型

Abstract: As a precipitation-strengthened nickel-based superalloy, GH4169 undergoes a gradual transformation of the γ″ strengthening phase into the δ phase during long-term service above 650 ℃, resulting in significant degradation of high-temperature strength. For long-term service components, the residual yield strength after high-temperature exposure is a key parameter for evaluating load-bearing capacity and fatigue life. However, the quantitative relationship among high-temperature precipitate transformation, morphology evolution, and residual strength degradation remains insufficiently understood. To address this issue, this study systematically investigated the precipitate evolution and yield strength variation of GH4169 alloys with three different initial microstructural states, namely the original, standard, and improved states, before and after high-temperature aging. The results show that aging at 800 ℃ significantly promotes the γ″→δ transformation. The original and standard samples are mainly characterized by intragranular precipitate coarsening and the growth of needle-like δ precipitates, whereas the improved sample primarily exhibits slow coarsening of grain-boundary δ precipitates. Based on microstructural characterization, a yield strength model considering the γ″→δ transformation and the morphology evolution of non-spherical precipitates was established using microstructural parameters, including grain size, matrix composition, precipitate size, precipitate volume fraction, and dislocation density. In the model, Nb-rich precipitates were classified according to morphology and size into nanoscale γ″ precipitates, granular/short-rod precipitates, and needle-like δ precipitates, and their strengthening contributions were evaluated separately. The predicted yield strengths agree well with the experimental values at room temperature and 650 ℃, with errors below 8%. The results provide a microstructure-parameterized methodological reference for evaluating the residual strength of GH4169 alloy after long-term high-temperature exposure.

Key words: GH4169 alloy, high-temperature aging, γ″→δ transformation, precipitate evolution, precipitation strengthening, yield strength model