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高铝钛铸造镍基高温合金有比重小、高温强度高、综合性能好的特点。合金中有γ固溶体、Ni_3(Al,Ti)、TiC、M_(23)G_6、γ′·C等主要相,成分出格或工艺控制不当时,可能出现σ、μ或M_6C相。调整合金元素的种类和数量,对合金的相组织有决定性的作用,影响持久强度等性能和σ相的析出,其中以铬、铝、钛最为关键。如γ′强化相大量析出后,基体中富集易形成σ相的铬、钼、钴等元素,给σ相的形成创造条件。合金中铝钛总量愈高,γ′相愈多,γ基体中铬含量逐渐增多,将促进σ相析出。如铝铬量一定,随着钛的增多,基体中铬、钼和钴趋向增加,也促使σ相析出。铝钛增多,钛的树枝状偏析严重,能引起(γ+γ′)共晶增多,σ相往往在时效过程中于(γ+γ′)共晶周围析出。经变化合金中铝、钛、铬的含量,研究其持久强度和瞬时性能等的影响,得出一般情况下可用9Cr系,铝钛总量可在10.2至11.4%之间,其900℃,32公斤/毫米~2下的持久时间超过100小时,瞬时性能良好。只要铝保持5.5%,则钛可由4%至5.5%。其它如钼、碳、硼、钴、钒等均分别予以研究讨论。防止析出σ相,除控制铬、铝、钛等的含量合格外,还必须注意铸造工艺,密切注意铸温和造型技术,减少偏析。合金有良好的组织稳定性,不需要热处理,而且冶炼和铸造工艺均不复杂,便利生产。
High-aluminum titanium casting nickel-based superalloy a small proportion, high temperature strength, good overall performance characteristics. The alloy has γ solid solution, Ni_3 (Al, Ti), TiC, M_ (23) G_6, γ’C and other major phases. When the composition is out of control or the process is improperly controlled, σ, μ or M_6C phases may appear. Adjusting the type and amount of alloying elements has a decisive effect on the phase structure of the alloy, affecting the properties such as long-term strength and the precipitation of the σ phase, of which chromium, aluminum and titanium are the most important ones. For example, when a large amount of γ ’strengthening phase is precipitated, elements such as chromium, molybdenum and cobalt which are apt to form a σ phase are enriched in the matrix, thereby creating conditions for the formation of σ phase. The higher the total amount of aluminum-titanium in the alloy, the more γ ’phase, the more the content of chromium in γ matrix will increase, which will promote the precipitation of σ phase. As a certain amount of aluminum chromium, with the increase of titanium, chromium, molybdenum and cobalt matrix tends to increase, also prompted the precipitation of σ phase. Al-Ti increases and the dendritic segregation of titanium is serious, which can cause the increase of (γ + γ ’) eutectic. The σ phase tends to precipitate around the (γ + γ’) eutectic during the aging process. The contents of Al, Ti and Cr in the alloy were studied to study the influence of the long-term strength and transient properties. The results show that under normal conditions, the total amount of 9Cr and Al-Ti can range from 10.2 to 11.4% Persistence of more than 100 hours in kg / mm ~ 2, instantaneous performance is good. Titanium can be from 4% to 5.5% as long as the aluminum remains 5.5%. Other such as molybdenum, carbon, boron, cobalt, vanadium, etc. were discussed separately. Prevent the precipitation of σ phase, in addition to controlling the content of chromium, aluminum, titanium and other qualified, we must also pay attention to the casting process, pay close attention to casting mild modeling techniques to reduce segregation. Alloy has good tissue stability, does not require heat treatment, and smelting and casting process are not complicated, facilitate the production.