5. Conclusions

A mechanistic based cavitation model that considers nucleation, early-stage growth and sintering under multi-cycle creep-fatigue interaction has been developed to provide predictions of both the number density of cavities and the area fraction of cavitated grain boundaries in Type 316 stainless steel. The model replies on the local normal stress to connect the three concurrent or sequential cavitation events, providing important insights about how to design the creep-fatigue load waveform so that the creep cavitation can be enhanced. The following conclusions can be reached:
  1. When tensile hold time is longer than that of compression, the creep-fatigue test with initial compression is advantageous in terms of creating more cavities.
  2. Unbalanced stress hold time in favour of compression most likely closes all of the cavities nucleated during the previous tension phase.
  3. Effect of compressive hold time or stress level on the number density of cavities in creep-fatigue tests is not monotonic. The underlying mechanism is their competing effect on nucleation and sintering.
  4. There is an optimum value for the stress variation rate to obtain the highest number density of cavities, and their presence can be attributed to sintering effect.
  5. Our model can satisfactorily explain several interesting experimental observations, including nucleation incubation time, effective nucleation field in a stress-frequency space for high-temperature fatigue, and the effect of unequal ramp rate on cavitation.