高温合金服役过程中的热力耦合状态可使组织发生退化，进而影响其力学性能。对FGH4720Li粉末高温合金在近服役状态下的组织与性能演变规律进行研究，可为同类合金用于涡轮盘的制造提供参考。本工作对FGH4720Li粉末高温合金在500 MPa、600和650 ℃下进行500、1000和2000 h持久实验，研究其在持久实验过程中的组织演变规律及在650 ℃持久实验后合金屈服强度的变化规律。结果表明，FGH4720Li粉末高温合金在650 ℃持久实验后屈服强度维持在约1120 MPa，合金中二次γ'相的形貌由椭球状逐渐变为花瓣状最后演变为带圆角的立方状，三次γ'相出现聚合粗化现象。采用高γ'相含量且强化相多模态分布的沉淀强化预测模型计算了持久实验后合金的屈服强度，进一步证明了三次γ'相含量和尺寸的变化是引起合金屈服强度变化的主要原因。

The FGH4720Li superalloy is produced by GH4720Li through the powder metallurgy (P/M) process, a method that effectively addresses the shortcomings of the original alloy production process, such as significant segregation, low alloying levels, and manufacturing difficulties. The P/M method also results in a finer and more uniform microstructure. However, during the service life of superalloys, the thermodynamic conditions can degrade the microstructure, potentially affecting their mechanical properties. There is currently limited research on how the microstructure and properties of FGH4720Li P/M superalloy evolve under near-service conditions. Therefore, it is essential to investigate this evolution to provide valuable insights for the manufacture of turbine disks. In this study, the microstructure evolution of FGH4720Li P/M superalloy and the variations in its yield strength have been examined after subjecting it to stress rupture for 500, 1000, and 2000 h at 600 and 650 ^oC under a stress level of 500 MPa. The results show that the yield strength of FGH4720Li P/M superalloy remains relatively high, at 1120 MPa, after stress rupture at 650 ^oC. Furthermore, the microstructure of FGH4720Li P/M superalloy undergoes a complex transformation during stress rupture. The secondary γ' phase's morphology gradually changes from an ellipsoidal shape to a flowerlike shape and ultimately to a cubic shape with rounded corners. The coarsening in the polymerization growth of tertiary γ' phases is also observed. To understand the changes in yield strength after stress rupture, a precipitation strengthening prediction model specifically designed for high γ' phase content and a multi-mode distribution of γ' phases was utilized. This calculation confirmed that the alteration in the content and size of the tertiary γ' phase is the primary factor responsible for the yield strength changes in the alloy.