Evolution Law of γ' Precipitates in New Directionally Solidified Nickel-Base Superalloy DZ445 at High Temperatures

Evolution law of γ' strengthening precipitates at high temperatures in a new directionally solidified nickel-base superalloy DZ445 was studied by thermal exposure tests at 800-900 ℃. The results show that at high temperatures, the growth of γ'precipitates was controlled by diffusion of matrix elements, and the growth kinetics followed the Lifshitz-Slyozov-Wagner ripening law; the diffusion activation energy was 305 kJ·mol^-1. The microstructure of the alloy was stable. Even after thermal exposure at 900 ℃ for 10 000 h, the average particle size of γ' precipitates only increased to (928±14) nm. The volume fractions of γ' precipitates remained about 50% in thermal exposure at 800-900 ℃ for 10 000 h, and no topologically close-packed phase was observed. During thermal exposure at 850 ℃ and 900 ℃, the shape of γ' precipitates changed from spheroidal to cubic or tetragonal, which was related to the particle size and lattice mismatch.