Long-term Aging Behavior and Mechanism of CMSX-4 Nickel-Based Single Crystal Superalloy at 950 ℃ and 1050 ℃

Nickel-based single crystal superalloys CMSX-4 have been widely used to manufacture aeroengine turbine blades because of their excellent high-temperature comprehensive properties. The microstructure evolution behavior, mechanism, and influence on micromechanical behavior of the second-generation nickel-based single crystal superalloy during long-term aging at 950 degrees C and 1050 degrees C for 10-2000 h were investigated. The results show that, with the extension of aging time, the average size of gamma' phase increased, whose morphology changed from square block to strip and L shape and rafting phenomenon was observed. The coarsening of gamma' conforms to Lifshitz-Slyozov-Wagner (LSW) theory and the coarsening rates are 4.241x10- 5 and 9.954x10- 5 mu m3/h at 950 degrees C and 1050 degrees C, respectively. After aging at 950 degrees C and 1050 degrees C for 1000 h, segregation of refractory elements was formed in the samples. There are hard topological close-packed (TCP) phases surrounded by gamma' envelope precipitates, which destroyed the continuous structure of gamma'. The precipitation of TCP caused the depletion of refractory element Re in the gamma' envelope phases, resulting in softening effect. It was also found that high temperature can not only accelerate the coarsening of gamma' phase but also promote the precipitation and growth of TCP phases.