一种新型镍基合金相的析出规律

Phase Precipitation of a New Kind of Ni-Base Superalloy

采用物相分析和透射电镜(TEM)方法研究了GH4199合金中不同温度长期时效处理条件下相的析出规律·结果表明,合金经长期时效处理后γ′相在700～800℃时析出比较充分,800℃以上开始回溶,γ′相在高温长期时效过程中的长大规律符合Ostwald理论,同时合金中有TCP相的析出·GH4199合金电子空位数为2 31到2 35,比镍基合金中μ相析出的临界电子空位数2 30略大,故当合金在高温下具有足够的热暴露时μ相会析出;合金的电子空位数虽不高于σ相析出的临界值,但由于γ′相的大量析出,造成合金基体中的Cr,Mo等形成σ相元素局部相对含量剧增,有可能导致σ相析出·

GH4199 alloy is a newly developed Ni-base superalloy which is precipitation hardened by an Ni_3(Al,Ti) γ′ phase with orderly fcc structure. The γ′ phase precipitates coherently in nickel-rich fcc γ matrix. The phase precipitation behaviour in GH4199 was studied by means of phase analysis technology and TEM observation, as well as the calculation of electron vacancy number. Experimental results showed that almost a maximum amount of γ′ precipitates can be found at 700～800℃ and it begins to dissolve at above 800℃. Furthermore, the harmful brittle TCP phase can be found in this alloy at the temperature range of 700℃ to 950℃ after long-term aging. The electron vacancy number in GH4199 is 2.31～2.35, which is higher than that of critical number of μ phase formation, as shown in reference. Therefore, μ phase can be precipitated under thermo-exposure conditions. In contrast, the σ phase is also observed by TEM. The calculated electron vacancy number is less than the critical number (2.52) of σ phase formation as given by reference. The enrichment of Cr and Mo in γ-matrix after a large amount of γ′ phase precipitation leads the σ phase to form in GH4199.