FATIGUE CRACK-GROWTH THROUGH PARTIALLY-STABILIZED ZIRCONIA AT AMBIENT AND ELEVATED-TEMPERATURES

Fatigue crack growth through magnesia stabilized zirconia at 20, 450 and 650-degrees-C has been observed dynamically in a high temperature loading stage for the scanning electron microscope. Crack tip micromechanics parameters were measured using the stereoimaging technique. Fatigue crack growth at ambient temperature was found to be very similar to crack growth through metallic alloys. With increasing temperature, the stress intensity levels in which stable fatigue crack growth could be sustained were found to narrow significantly, until fatigue is expected to not be a valid mechanism of crack growth above about 750-degrees-C. Measured crack tip parameters were used to derive the low-cycle fatigue and the stress-cycles to failure characteristics. The latter agreed with measured SN curves. Deformation within the plastic zone was shown to account for the measured value of fracture toughness. The mechanisms of crack growth are discussed.