Microstructural Stability and Stress Rupture Properties of a Third-Generation Ni Base Single Crystal Supalloy

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 degrees C 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 degrees C 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.