FATIGUE CRACK-PROPAGATION IN CERIA-PARTIALLY-STABILIZED ZIRCONIA (CE-TZP)-ALUMINA COMPOSITES

Fatigue crack propagation rates in tension‐tension load cycling were measured in ZrO2‐12 mol% CeO2‐10 wt% Al2O3 ceramics using precracked and annealed compact tension specimens. The fatigue crack growth behavior was examined for Ce‐TZPs of different transformation yield stresses obtained by sintering for 2 h at temperatures of 1500°C (type A), 1475°C (type B), 1450°C (type C), and 1425°C (type D). The threshold stress‐intensity range, ΔKth, for initiation of fatigue crack propagation increased systematically with decreasing transformation yield stress obtained with increasing sintering temperature. However, the critical stress‐intensity range for fast fracture, ΔKc, as well as the stress‐intensity exponent in a power‐law correlation (log (da/dN) vs log ΔK) were relatively insensitive to the transformation yield stress. The fatigue crack growth behavior was also strongly influenced by the history of crack shielding via the development of the crack‐tip transformation zones. In particular, the threshold stess‐intensity range, ΔKth, increased with increasing size of the transformation zone formed in prior quasi‐static loading. Crack growth rates under sustained peak loads were also measured and found to be significantly lower and occurred at higher peak stress intensities as compared to the fatigue crack growth rates. Calculations of crack shielding from the transformation zones indicated that the enhanced crack growth susceptibility of Ce‐TZP ceramics in fatigue is not due to reduced zone shielding. Alternate mechanisms that can lead to reduced crack shielding in tension‐tension cyclic loading and result in higher crack‐growth rates are explored. Copyright © 1990, Wiley Blackwell. All rights reserved