热暴露时效对DD6合金组织和强度的影响

Effect of Thermal Exposure Aging on Microstructure and Strength of DD6 Alloy

摘要:

对DD6镍基单晶高温合金进行热暴露时效处理获得不同程度的退化组织，研究组织退化演变机理以及对应剩余强度和断裂机理，并探讨组织退化损伤程度的参量表征方式，建立组织退化损伤程度与剩余强度间的量化映射关系。结果表明，在热暴露时效过程中，γ′相按照Ostwald熟化机制回溶或长大，980 ℃下1190 h和1100 ℃下100 h后γ′相含量已基本达到热力平衡态，γ相和γ′相随着温度升高和时间延长继续粗化并趋于稳定，最终γ相宽度约400 nm和γ'相宽度约760 nm。在粗化的同时，DD6合金在内部γ/γ′相错配应力或外加应力作用下，组织发生筏化。粗化和筏化均降低了合金的强度。综合考虑粗化和筏化作用，本研究采用微观结构尺寸参量ωλ²与剩余强度建立了良好的量化映射关系式，且该损伤量化表征方式不受合金初始态微观结构尺寸的约束。

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.