高性能镍基粉末高温合金固溶连续冷却γ′相多阶段析出行为和尺寸粗化动力学研究

Study on the kinetics and reverse coarsening effect of multi generations precipitation during continuous cooling in high performance Ni-Base PM Superalloy

摘要:

本文采用示差扫描量热分析和热模拟连续冷却实验,系统地研究了新型高性能三代粉末高温合金在γ′相固溶线温度以上连续冷却过程中强化相γ′相多批次析出行为。研究结果表明,合金在0.1和0.4 ℃.s_-1冷却速率下可以获得γ′相多模尺寸分布显微组织。这种γ′相多批次析出与冷却速率密切相关,缓慢冷却是造成γ′相尺寸多模分布的主要因素。采用线性回归方法拟合得到二次γ′相平均尺寸与冷却速率定量关系。分析和讨论了在γ相基体上形成多模γ′相尺寸分布的动力学机理。对具有多模γ′相尺寸分布的合金进行时效处理发现,由于合金显微组织中大尺寸二次γ′相的形态不稳定,出现γ′相反粗化现象,即随着时效时间增加,γ′相尺寸逐渐减小。这种反粗化效应使合金强度升高,增强合金显微组织稳定性。讨论了反粗化效应的发生条件,对研发新型高性能粉末高温合金提供制造工艺和组织调控的理论依据。

Abstract:

Differential scanning calorimetry (DSC) and thermal simulation continuous cooling experiments were used to systematically study the behavior and microstructure of γ′ multi generations precipitation during the continuous cooling process in the third generation high performance PM superalloy. The results show that the alloy can obtain a multimodal size distribution of γ′ precipitates at cooling rates less than 1.4 ℃/s-1. The multi generations precipitation is closely related to the cooling rates. The slow cooling is the dominant factor causing the multimodal size distribution of γ′ precipitates. The linear regression method is used to get the quantitative relationship between the average sizes of secondary γ′ and cooling rates, and the formation kinetics and mechanism of multimodal size distribution of γ′ precipitates on the γ matrix are analyzed and discussed. Results of long-term aging of alloy with γ′ multimodal size distribution show that reverse coarsening phenomenon occurs due to the unstable morphology of the large-size secondary γ′, i.e., the average size of γ′ precipitates decreases with the increase of aging time. This reverse coarsening effect increases the strength of the alloy, and increases the long-term stability of the microstructure of the alloy. The conditions and reasons for the reverse coarsening of γ′ are also discussed. This work will provide a theoretical basis for the further research and development of new high performance PM superalloys.