利用场发射扫描电镜和萃取相分析等方法对FGH4720Li合金在600~730℃下时效3000 h过程中的组织演变进行了观察和分析。结果表明，γ'_Ⅰ相最为稳定，而γ'_Ⅱ和γ'_Ⅲ相则会发生复杂变化。600℃下时效时，合金组织无明显变化；在650℃下时效3000 h后，仅有γ'_Ⅲ相发生长大，其他γ'相无明显变化；当时效温度升高到730℃，γ'_Ⅲ相的长大速率加快，然后迅速粗化，时效200 h后，γ'_Ⅱ相发生粗化，但B-γ'_Ⅱ相会先发生Ostwald熟化现象，吸收大量γ'_Ⅲ相而粗化，并且在300~500 h之间发生分裂，然后在500 h后通过互相聚合而粗化，而S-γ'_Ⅱ相则始终通过互相聚合的方式来粗化。2种γ'_Ⅱ相粗化行为的差异与γ'_Ⅲ相的分布特征有关。

GH4720Li is used for turbine disks in a large number of civil and military propulsion systems because of its excellent mechanical properties and corrosion resistance. GH4720Li turbine disk is mainly manufactured through cast and wrought conventionally, but the addition of a high mass fraction of Ti, Al, and Mo can cause severe element segregation and more difficult microstructure control, which can become more severe as the turbine disk gets larger. Owing to this difficulty, the turbine disk quality cannot be guaranteed if the GH4720Li turbine disk is still in cast and wrought form, and the manufacturing process will be more complex, resulting in increased costs. However, the powder metallurgy method can efficiently eliminate element segregation and produce a more uniform microstructure than the cast and wrought methods. GH4720Li alloys manufactured using the powder metallurgy method are called FGH4720Li alloys. As there has been limited research on FGH4720Li and no report on the microstructure evolution during long-term ageing for FGH4720Li to date, it is necessary to study the microstructure evolution behavior during long-term ageing for FGH4720Li to obtain improved microstructure stability. In this study, field emission scanning electron microscopy and extractive phase analysis were used to investigate the microstructure evolution of FGH4720Li in the temperature range of 600-730^oC up to 3000 h. The results showed that primary gamma prime was the most stable; whereas, secondary and tertiary gamma prime microstructure evolutions were comparatively complex. At 600^oC, there was no microstructure change. At 650^oC, only the tertiary gamma prime grew, but there was no microstructure change for the other gamma primes up to 3000 h. When the ageing temperature increased to 730^oC, the tertiary gamma prime grew faster before coarsening rapidly. After 200 h, the secondary gamma prime coarsened noticeably, but the big secondary gamma prime coarsened by Ostwald ripening first, absorbing a large amount of tertiary gamma prime and splitting up between 300 and 500 h, before ageing with further processing. Big secondary gamma prime mainly coarsens by amalgamation; whereas, small secondary gamma prime always coarsens by amalgamation during ageing. The divergence between these two types of secondary gamma prime is related to the distribution characteristics of the tertiary gamma prime.