Dependence of Creep Performance and Microstructure Evolution on Solution Cooling Rate in a Polycrystalline Superalloy

It is well known that the solution cooling rate has a great effect on the creep life of superalloys. In this research, three typical cooling rates were applied to generate different distributions of γ’ precipitates for creep tests. Ingots used to make specimens were manufactured by hot extrusion, and the master alloy had the composition of an FGH4096 power metallurgy superalloy. SEM and SESD were used to observe the microstructure’s evolution. The experimental results show that the fastest cooling rate corresponds to the highest creep life as well as the smallest rupture strain, and vice versa. The microscopic observations disclose that with an increasing cooling rate, the size and area fraction of γ’ precipitates decrease, and the rupture mechanism changes from transgranular to intergranular. Moreover, some γ’ precipitates changed to cuboid after the creep test. The results will provide new technological processes to design more creep-resistant, nickel-base superalloys.