Re和Ta对抗热腐蚀单晶高温合金900℃长期时效组织稳定性的影响

The development of gas turbines urgently requires the development of new single crystal superalloys with capacity to service for long time at higher temperature and under hot corrosion environment. In order to take into account both the strength and structural stability of the alloy, it is an effective way to increase the content of key strengthening elements Re and Ta reasonably, and control the mismatch of γ/γ' to delay the growth kinetics of γ'. In this work, the long-term thermal exposure (LTTE) experiments of single crystal superalloys with different Re and Ta contents at 900 ℃ were carried out. The evolution of morphology and size of γ', and the precipitation of topological close-packed (TCP) phase during 0~ 7500 h ageing process were quantitatively analyzed. The results show that the size and the coarsening rate of γ' phase decreases with the increase of Ta and Re content in 2Ta2Re, 5Ta0Re, 5Ta2Re, 8Ta0Re and 8Ta2Re alloys. The coarsening rates are 1.445×10^-5, 1.569×10^-5, 1.390×10^-5, 1.465×10^-5and 1.384× 10^-5 μm³/h respectively. With the increase of Ta and Re content, the effective diffusion coefficient decreases and the diffusion activation energy increases, thus of the coarsening rate of precipitated phase decreases. After ageing for 2000 h, TCP phase was precipitated in turn in alloys containing Re, and the precipitation of TCP phase was more serious in alloys containing higher content of Ta. The interaction between Ta and Re affects the atomic distribution behavior of elements in γ and γ', in which 8Ta2Re alloy Ta enters the γ' phase to increase its lattice constant, and at the same time promotes the distribution of elements such as Re, W and Cr in the γ matrix, which results in more negative γ/γ' mismatch and promotes the precipitation of TCP phase.