材料期刊网

利用光学显微镜、场发射SEM等手段,对标准热处理（1080℃×4 h/AC＋845℃×24h/AC＋760℃×16h/AC）后的GH864镍基合金分别在650℃和870℃进行长期时效,研究长期时效温度和时间对合金组织和性能的影响。结果表明,GH864合金在650℃时效1000 h过程中,随着时间的延长γ＇相长大不明显,晶界碳化物及γ＇相尺寸分布状态几乎保持不变,基体中有三次γ＇相析出,随着时效时间延长硬度增加,体现了合金在该温度下良好的组织稳定性;在650℃及870℃长期时效,γ＇相随温度升高及时间延长而粗化,其规律遵循L-S-W理论,且温度越高,粗化速率也越大,温度比时间的影响更为明显;在870℃温度时效3000 h过程中,γ＇相急剧长大及其体积分数逐渐降低,γ＇相时效后期的长大速率较初期减缓;同时,合金中的晶界碳化物逐渐溶解消失,局部位置γ＇相完全溶入基体并导致复杂的合金元素反应,形成复杂组织,最终导致合金硬度下降,合金发生了明显退化。

Degradation behavior of microstructure of GH864 alloy after exposure at 650 ℃ and 870 ℃ for long to 3000 h were investigated by optical microscope and field emission SEM.The results show that γ′ strengthening phase and carbides at grain boundary of GH864 alloy exhibit no significant change during long exposure at 650 ℃,however,there are tertiary γ′ precipitates,and hardness of the alloy increases with the ageing time prolonging.Therefore,it indicates that microstructures of the alloy at 650 ℃ is much stable.Long exposure at 650 ℃ or 870 ℃,the coarsening rate of γ′ phase gradually increases with increasing temperature and time,and the coarsening behavior of γ′ phase meets the LSW aging theory.The growth rate of γ′ phase in the early stage is higher than that in the later stage,while the influence of temperature on the coarsening rate is more obvious than time.During aging at 870 ℃,the size of γ′ phase grows up sharply and the relative volume fraction of γ′ phase gradually decreases with aging time.Meanwhile,the carbides at grain boundary gradually dissolve and disappear.In local position,complex reaction occurrs by complete dissolution of γ′ phase,eventually leading to the decreases of hardness of GH864 alloy,which is suggested that the GH864 alloy is obviously degraded.