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以服役900 h的DZ125合金叶片为研究对象, 通过对叶片服役前后的枝晶干、枝晶间、晶界及碳化物各类组织退化行为的研究, 确定了枝晶干γ’相的体积分数作为反映服役温度的可量化表征参量. 结合叶片用DZ125合金在900~1100 ℃下显微组织的演变行为, 研究了热暴露温度与枝晶干γ’相体积分数之间的量化对应关系. 在此基础上, 提出了一种基于显微组织的涡轮叶片服役温度的实验评估方法. 同时, 分别假设叶片服役温度恒定以及考虑叶片实际服役温度变化2种情况, 实现了对等效平均服役温度(T_ave)及等效最高服役温度(T_max)的定量评估. 评估结果表明: 叶片叶身中部服役温度最高, 由叶身中部向叶尖和叶根服役温度逐渐降低; 同一截面服役温度由高到低依次为: 进气边>叶盆>排气边>叶背; 服役温度最高的区域为叶身中部截面的进气边, 服役时经历的等效最高服役温度为1050~1100 ℃. 叶片等效平均服役温度及等效最高服役温度的分布规律一致, 但部分部位的等效最高服役温度高于等效平均服役温度, 本研究认为叶片的等效最高服役温度的评估结果更为合理.

To get the actual service temperature distribution of turbine blades in aeroengines is very important for the design and maintenance. However, the acquisition of service temperature distribution has always been a challenge due to the complex and severe working condition of turbine blades. In this work, one turbine blade made of directionally solidified DZ125 superalloy was investigated after the service in air for 900 h. The microstructural evolution of DZ125 superalloy after thermal exposure at 900~1100 ℃ without the stress in different time period was also investigated, for comparison. According to microstructural degradation behaviors in the dendritic region, interdendritic region, carbides and grain boundary of DZ125 superalloy before and after service, the volume fraction of γ’ precipitates in the dendritic region was determined as the quantitative characterization parameter. A method to evaluate the service temperature of turbine blades was developed, based on the quantitative characterization of microstructural evolution, such as the relationship between the thermally exposured temperature and volume fraction of γ’ precipitates. The equivalent average service temperature (T_ave) and the equivalent maximum service temperature (T_max) were proposed based on the assumption of the constant temperature during service and the nearly service condition with variable temperature of blades, respectively. The results indicate that the service temperature was higher in the middle of the blade, and became lower at the locations closer to the tip or the root. For each cross-section, the service temperatures of the serviced blade in the descending order were leading edge, pressure side, trailing edge and suction side. The highest service temperature of 1050~1100 ℃ appeared at the leading edge in the middle of the blade. The distribution trend of T_ave agreed well with that of T_max, but T_max was higher than T_ave in some locations of the blade. This work suggests that the evaluation results of T_max were more reasonable than those of T_ave. This method would be helpful to establish the assessment method of the service-induced microstructural damage in turbine blades made of directionally solidified superalloys.