Thermodynamic Study on Denitrification and TiN Precipitation in IN718 Nickel Base Superalloy Melt

doi:10.20057/j.1003-8620.2023-00113

Abstract

Abstract: Low nitrogen content can control the formation of TiN inclusions， thereby improving the metallurgical quality and comprehensive performance of nickel based high-temperature alloys. This article first compared the differences between the standard Gibbs free energy and the interaction coefficient of alloy elements with N， Ti activity in nickel based and iron based metal liquids， it pointed out that two different sets of thermodynamic data from nickel based and iron based metal liquids cannot be mixed.The thermodynamic model for nitrogen removal of IN718 alloy was established based on the existing thermodynamic parameters of nickel based alloys. It was found that reducing temperature and increasing vacuum degree to reduce nitrogen partial pressure while meeting other smelting conditions are the direct means to reduce nitrogen content in the alloy liquid. The addition of different alloying elements has different effects on nitrogen removal. At the same time， the thermodynamic model and segregation model for TiN precipitation were established， and the calculation results showed that under the production temperature of IN718 at 1 450 ℃， the ［N］ content in the alloy liquid was controlled below 43.69×10^-6， the solute elements N and Ti are enriched and precipitated in the liquid phase during solidification. The calculated precipitation temperature is 1 468 K， and the solid fraction is fs 0.829. If we want to control the solid phase fraction fs to be above 90% or 95% respectively for precipitating TiN inclusions，［N］ needs to be controlled below 25.00×10-⁶ and 15.00×10^-6 respectively.

Key words: Nickel Base Superalloy, Denitrification, TiN Precipitation, Thermodynamics

摘要： 低氮含量可控制TiN夹杂物生成，从而提高镍基高温合金冶金质量和综合性能。通过比较镍基和铁基金属液中标准吉布斯自由能和合金元素对N、Ti活度相互作用系数的差别，指出镍基和铁基中两套不同的热力学数据，二者不能混用。以目前已有的镍基高温合金的热力学参数建立了IN718合金脱氮热力学模型，得出在满足其他冶炼条件的前提下，适当降低温度和提高真空度以降低氮气分压是降低合金液中氮含量的直接手段，以及不同合金元素加入对脱氮的影响不同。同时，建立TiN析出的热力学模型以及偏析模型，计算结果得出，在IN718的生产温度1 450 ℃条件下，控制合金液中的w［N］在43.69×10^-6以下，凝固过程中溶质元素N、Ti在液相中富集TiN析出，计算析出温度为1 468 K，此时固相分率f_s为0.829。若要控制固相分率f_s分别在90％或95％以上才会析出TiN夹杂物，w［N］需分别控制在25.00×10^-6和15.00×10^-6以下。

关键词: 镍基高温合金, 脱氮, TiN析出, 热力学

CLC Number:

TF701

Luo　Xiaoyu, Guo　Jing, Guo　HanJie, Li　Zeyou. Thermodynamic Study on Denitrification and TiN Precipitation in IN718 Nickel Base Superalloy Melt[J]. Special Steel, 2024, 45(1): 33-41.

罗小雨, 郭靖, 郭汉杰, 李泽友. IN718镍基高温合金熔体脱氮和TiN析出热力学研究[J]. 特殊钢, 2024, 45(1): 33-41.

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