关键词: 长期时效, γ′相, 碳化物, TCP相, 电子空位数

Abstract: GH4199 alloy is a newly developed Ni-base superalloy which is precipitation hardened by an Ni3(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°C and it begins to dissolve at above 800°C. Furthermore, the harmful brittle TCP phase can be found in this alloy at the temperature range of 700°C to 950°C 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.