How does phase transformation affect the fatigue behavior of 3Y-TZP in cryogenic environment?

The present work was to investigate the fatigue behavior of 3Y-TZP in cryogenic environment. The crack velocity versus the applied stress intensity (v-KI) curve presented two different stages and a larger threshold value KI0 during propagating in liquid nitrogen (LN2). For comparison, the static load crack growth test was also conducted on 3Y-TZP under ambient conditions (RT), primarily to understand the difference in fatigue behavior mechanisms in liquid nitrogen environment. Confocal Raman spectroscopy was used to estimate the extension of the tetragonal to monoclinic (t→m) phase transformation. For the first time, we have directly visualized the phase-transformation evolution directly around the very tip of crack propagation in liquid nitrogen environment. With these arranged experiments, it was attempted to answer two important issues: (i) Did the mechanism of fatigue behavior change from RT to LN2? (ii) How did t→m phase transformation affect the fatigue behavior in cryogenic environment? The experimental results suggested that there was an accumulation of crack tip shielding of 3Y-TZP induced by the phase transformation during crack propagation that limited the crack growth rate in cryogenic environment. This work was significant in understanding the service behavior of 3Y-TZP as structural components in cryogenic applications.