6 | CONCLUSION
The CCF test system, which can apply the high and low cycle loads simultaneously without interfering each other, is designed to study the effect of PSP treatment on the CCF life of turbine blades. The untreated and PSP treated full-scale turbine blades are tested. The results are summarized as following:
  1. According to the σH-N curves, the threshold vibration stress is determined to be 194.0MPa. The PSP treatment has the positive effect on the CCF life of turbine blades, only when the vibration stress is below the threshold vibration stress. While the vibration stress is above the threshold value, the PSP treatment has no or the negative effect on the CCF life.
  2. The PSP treatment results in the compressive residual stress in the treated area. When the vibration stresses are below the threshold vibration stress, the number of crack sources and crack growth rate decreases due to the compressive residual stress.
  3. The compressive residual stress is found to be released along with the microstructure change of K403 when the vibration stresses are above the threshold value. The lamellar MC carbides and σ phases precipitate from the matrix. These microstructure changes accelerate both the initiation and propagation process of cracks. Therefore, the CCF life of the PSP treated blades reduces compared with that of the untreated blades.