精确控冷热处理对盘用粉末高温合金FGH4113A高温塑性的影响

Effect of Precisely-Controlled Cooling Heat Treatment on High-Temperature Ductility of Powder Metallurgy Superalloy FGH4113A for Turbine Disks

摘要:

以粉末高温合金FGH4113A为研究对象，设计并实施了固溶阶段精确控冷，研究了不同冷却路径对其微观组织演变及800 ℃拉伸性能的影响机制。结果表明，冷却路径对合金的强度-塑性协同性具有重要影响。采用传统的150 ℃/min连续冷却工艺时，合金800 ℃拉伸屈服强度为920±7 MPa，抗拉强度为1079±9 MPa，断后延伸率为13.4%±2.9%。相比之下，采用第一阶段慢冷（44~75 ℃/min）与第二阶段快冷（459~594 ℃/min）相结合的工艺（CP2），屈服强度和抗拉强度分别提升至978±7和1112±5 MPa，同时延伸率优化至14.6%±1.1%。通过将工艺参数优化为第一阶段48~65 ℃/min冷却及第二阶段275~326 ℃/min冷却（CP3），在保持屈服强度975±10 MPa、抗拉强度1108±6 MPa的同时，将延伸率提升至18.5%±0.8%。微观组织表征揭示，阶段控冷工艺通过高温区间慢冷促进位错回复与中温区间快冷冻结低缺陷结构的组合，有效获得了低晶粒取向差、低位错密度的晶粒组织。此外，γ''相析出行为分析表明，第一阶段冷却速率主导了二次γ''相的尺寸，第二阶段冷却速率会影响三次γ''相的尺寸，而冷速转折温度则调控三次γ''相的体积分数。通过γ''相的多尺度协同分布，具体而言，适中的二次γ''相通过促进位错绕过机制，增强材料的应变硬化能力；弥散分布的三次γ''相则通过位错切割机制补偿二次γ''相粗化造成的强度损失。本研究表明，阶段精确控冷是一种无需改变合金成分即可实现FGH4113A粉末高温合金的800 ℃强度-塑性协同优化的有效途径，为该合金的热处理工艺设计提供理论依据和实践指导。

Abstract:

This study investigated the powder metallurgy superalloy FGH4113A, focusing on the design and implementation of precisely controlled cooling during the solid solution state. The effect of cooling path on microstructural evolution and tensile properties at 800 ℃ was examined. The results show that the cooling path significantly affects the strength-ductility synergy. At a conventional continuous cooling rate of 150 ℃/min, the alloy exhibits a yield strength of 920±7 MPa, an ultimate tensile strength of 1079±9 MPa, and an elongation of 13.4%±2.9%. In contrast, a two-stage cooling process (CP2), combining an initial slow cooling (44–75 ℃/min) with a subsequent fast cooling (459–594 ℃/min), enhances the yield strength and ultimate tensile strength to 978±7 and 1112±5 MPa, respectively, while also improving the elongation to 14.6%±1.1%. Further optimization of the process parameters to an initial cooling rate of 48–65 ℃/min followed by a second-stage rate of 275–326 ℃/min (CP3) achieves an elongation of 18.5%±0.8% while maintaining high strength levels (yield strength of 975±10 MPa and ultimate tensile strength of 1108±6 MPa). Microstructural characterization shows that the staged cooling strategy effectively produces grain structures with low orientation spread and low dislocation density by promoting dislocation recovery via slow cooling at high temperature and then freezing the low-defect structures through fast cooling at medium temperature. Furthermore, analysis of γ'' precipitation behavior indicates that the primary cooling rate governs the size of secondary γ'' phase, the secondary cooling rate influences the size of tertiary γ'' phase, and the cooling transition temperature regulates the volume fraction of tertiary γ'' phase. Through this multiscale cooperative distribution of γ'' phases, moderately-sized secondary γ'' phase enhances strain hardening capacity by promoting the Orowan bypassing mechanism, while the finely-dispersed tertiary γ'' phase compensates for the strength loss associated with coarsened secondary γ'' phase through shearing mechanism. This work demonstrates that precisely controlled staged cooling is an effective pathway for synergistically optimizing the strength and ductility of FGH4113A superalloy at 800 ℃ without altering its chemical composition, providing both a theoretical basis and practical guidance for the heat treatment design of this alloy.