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:
- 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.
- 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.
- 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.