针对第三代单晶高温合金研制过程中析出少量拓扑密排相(TCP相)和中温性能偏低的问题，采用电子空位数计算，确定了对合金组织稳定性影响最显著的元素为Al，通过将Al含量降低0.4%，合金在1100℃、1000 h长期时效后完全无TCP相析出，实现了合金良好的组织稳定性。根据中温变形机制，认为合金中温持久性能偏低的原因为合金层错能偏低。确定合金成分的优化方案为在Al含量降低0.4%的基础上，少量降低Re和Co的含量以提高合金的层错能，通过将Re和Co含量分别降低0.25%和1%，合金在760℃、800 MPa的持久寿命由40 h提高到150 h，且合金的高温持久性能保持不变。在此基础上，确定了组织稳定且中/高温性能平衡的一种第三代单晶合金的最佳成分，并讨论了稳定合金组织和提高中温蠕变性能的原因。

Single-crystal superalloys have been developed to the 5th generation to improve their temperature capacity. Thus, a rare metal Ru is doped to the 4th and 5th generations based on the 6%Re (with the same mass fraction) contained in third-generation superalloys. Compared with Re addition in low-generation superalloys, improvement of temperature capacity decreases with Ru addition in high-generation superalloys; however, the cost of superalloys containing Ru has increased significantly. Therefore, considerable attention must be paid to the development of third-generation single-crystal superalloys because of their superior cost performance. Thus, considering the slight precipitation of the topologically close-packed (TCP) phase and low properties at the intermediate temperature of third-generation single-crystal superalloys, Al is considered as a significant element affecting microstructure stability, which is determined by calculating the number of electron vacancy (N_v). By reducing 0.4%Al, no TCP phase is precipitated in the superalloy after long-term thermal exposure at 1100^oC for 1000 h; therefore, good microstructure stability is obtained. The concentration of Re and Co is decreased slightly to increase the stacking fault energy of the superalloy and to enhance the properties at intermediate temperature. The stress rupture life at 760^oC and 800 MPa extends from 40 h to 150 h by reducing 0.4%Al followed with reduction of 0.25%Re and 1%Co. Moreover, the stress rupture properties at high temperature remain unchanged. Based on the abovementioned research, a third-generation single-crystal superalloy is developed, and the causes of stabilization of the microstructure and improvement to properties at intermediate temperature are also discussed.