Influence of environment on delayed failure of alumina ceramics

Subcritical crack growth in alumina ceramics is a phenomenon that arouses i nterest 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 envi ronment on subcritical crack-growth exponent for various alumina-base ceram ics is studied. A dynamic fatigue technique is utilized It is revealed that the subcritical crack-growth resistance of glass-bonded aluminas is signif icantly lower than that of high-purity alumina in air and in wafer. Only ne gligible difference was revealed in the delayed failure behaviour of cerami cs bonded with various common glassy phases. However, high-purify alumina c eramics are much more susceptible to fatiguing in an acidic environment com pared to the yttria-alumosilicate glass-bonded alumina: hydrochloric acid e nvironment reduces drastically the crack-growth velocity exponent due to th e low stress-corrosion resistance of magnesia-enriched interfaces in high-a lumina ceramics. (C) 1998 Elsevier Science Limited. All rights reserved.