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摘要
The high pressure turbine blades of gas turbines at the service time of 25 000 and 50 000 h were selected to evaluate the damage of microstructure and the deterioration of mechanical properties after long-term service of single crystal turbine blades. The metallographic structure quantitative analysis and microhardness test were conducted at the middle of the blade body. Then, the size of γ' phase, volume fraction of γ' phase, size of secondary γ' phase, width of γ matrix channel and the Vickers hardness at different service time and positions were measured. The results show that the coarsening degree of the size of γ' phase is various at different positions in the same leaf. Moreover, the γ' phase size at the leading edge and the trailing edge (at high temperature zone) is larger than that at the pressure side and suction side. While the γ' phase volume fraction is slightly smaller than that of the other two places. It is interesting to notice that the γ' phase size of serviced 50 000 h blade is greater than that of the serviced 25 000 h blade at the same position. However, the volume fraction displays the opposite law. Furthermore, the secondary γ' phase precipitates in some positions; meanwhile the width of the base channel significantly increases at the secondary γ' phase precipitation position. It is verified that the secondary γ' phase precipitation is related to the high working temperature and the way of cooling by air cooling/furnace cooling experiment of 1100℃/2 h. The TCP phase precipitates in the abnormally high temperature region, which is rich in the elements of W and Re. After analysis, the phase is identified as the μ phase. The microhardness at each position decreases at different service time. The decrease of microhardness and the increase of the size of γ' phase demonstrate that there is a negative correlation between them. On the contrary, the microhardness decreases with the decline of volume fraction, indicating that the microhardness is positively correlated with the volume fraction. Therefore, these results suggest that the γ' phase size and volume fraction can be used as the evaluation parameters for evaluating the damage of the material. However, when the harmful phase is precipitated or the material is in high stress, it is necessary to comprehensively consider the variation of the γ' phase parameter caused by the two factors, and the degradation of the material performance.
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