Influence of environment on delayed failure of alumina ceramics

Dynamic fatigue testing of various alumina ceramics in humid air, water, acidic, and alkaline environments was performed. It is shown that the fatigue resistance of glass bonded alumina in air and in water is significantly reduced compared with that for high purity magnesia doped alumina. The crack growth velocity exponent is independent of the composition of the glassy grain boundary phase, as well as of the water content in the environment. Hydrochloric acid slightly lowers the crack growth velocity exponent for yttria-alumosilicate glass bonded ceramics, whereas the exponent decreases drastically for the magnesia doped material in an acidic environment. Possible mechanisms controlling slow crack growth in the ceramics are outlined.