Influence of environment on delayed failure of alumina ceramics

Subcritical crack growth in alumina ceramics is a phenomenon that arouses interest with respect to the problems of performance of various engineering parts, e.g. seal rings, bearings, etc. The subcritical crack growth results in dependence of strength on time known as delayed failure. Effect of environment on subcritical crack-growth exponent for various alumina-base ceramics is studied. A dynamic fatigue technique is utilized It is revealed that the subcritical crack-growth resistance of glass-bonded aluminas is significantly lower than that of high-purity alumina in air and in wafer. Only negligible difference was revealed in the delayed failure behaviour of ceramics bonded with various common glassy phases. However, high-purify alumina ceramics are much more susceptible to fatiguing in an acidic environment compared to the yttria-alumosilicate glass-bonded alumina: hydrochloric acid environment reduces drastically the crack-growth velocity exponent due to the low stress-corrosion resistance of magnesia-enriched interfaces in high-alumina ceramics. (C) 1998 Elsevier Science Limited. All rights reserved.