Abstract: The changes of γ′ and η phases in LF9 nickel-based alloy after solution treatment at 800-1 040 ℃ for 1 h and then water quenched were studied by SEM,TEM,EDS and ICP-AES methods and the impact toughness of the alloy was measured using impact tester.The results showed that the γ′ phase in the alloy would grow up at high temperatures.For example,the average size of γ′ phase in original forging microstructure was about 20 nm,became 120 nm at 980 ℃ and dissolved completely at 1 020 ℃.The secondary parallel η phase grew up outward along grain boundaries at 820 ℃,reached peak value at 980 ℃ and dissolved completely at 1 040 ℃.At the same time,the γ′-depleted-zone appeared beside the growing η phase.The microplastic effect of the γ′-depleted-zone reduced the crack diffusion rate and thus improved the alloy ductility.However,the increase of the precipitation quantity and size of the η phase decreased the impact tonghness of the alloy.