The effect of anelasticity and phase transformation on crack growth in Y-TZP ceramics

Crack growth behavior has been investigated under monotonic and cyclic loadings for Y-TZP that produces remarkable anelastic strain. Monotonic loading testing was carried out under the condition of various stress rates (8 × 10², 8 × 10^–1 and 8 × 10^–4 MPa/s) and temperatures (RT and 373 K). Resistance of crack propagation was observed at the lowest stress rate at elevated temperature. Cyclic fatigue crack growth rate was examined under the condition of different frequencies and stress waveforms. Crack growth rate clearly depended on stress waveform, which was explicable by exhaustion and restoration of anelasticity at the crack tip region. Experimental results make it clear that anelasticity works as strong resistance against crack growth. In this study, the effect of environment-induced tetragonal to monoclinic phase transformation on fracture strength was also investigated for pre-cracked sample. Aged (transformed) samples have shown extreme crack closure and considerable improvement in strength.