新型定向凝固镍基高温合金DZ445中γ'相在高温下的演变规律
Evolution Law of γ' Precipitates in New Directionally Solidified Nickel-Base Superalloy DZ445 at High Temperatures
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摘要: 通过对新型定向凝固镍基高温合金DZ445进行800~900℃热暴露试验,研究了合金中γ'强化相在高温下的演变规律。结果表明:高温下γ'相的长大受基体元素扩散控制,长大动力学遵循Lifshitz-Slyozov-Wagner熟化规律,扩散激活能为305 kJ·mol-1;合金组织稳定,即使是在900℃热暴露10 000 h,γ'相颗粒的平均尺寸也只增大至(928±14) nm,在800~900℃下热暴露10 000 h时γ'相体积分数保持在50%上下,未观察到拓扑密堆相析出;在850,900℃热暴露过程中,γ'相形貌由类球状向立方或四方块状转变,这种转变与颗粒尺寸和晶格错配度有关。Abstract: 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.