Influence of the temperature on the strength and the subcritical crack growth rate of alumina

Dynamic four-point-bending tests between 20 and 900 degreesC were carried out in laboratory air on an alumina ceramic with a few intergranular glass phases (MgO, SiO2, CaO). The inert strength decreases with increasing temperature from 25 to 900 degreesC. In this range the temperature has no influence on the values of the corrected Weibull modulus M-k. This means, that the strength distribution of the alumina investigated did not depend on the test temperature. The subcritical crack growth parameter A increases with increasing temperature from 25 to 500 degreesC and then decreases with further increasing temperature up to 900 degreesC. In contrast to this behaviour, for the parameter n the opposite temperature dependence turns out; n decreases between 25 and 500 degreesC and then increases. From da/dt-K-I plots it can be seen that the subcritical crack growth behaviour changes at a temperature of about 500 degreesC. For a constant crack propagation rate K-I decreases with increasing temperature from 25 to 500 degreesC and then increases with further increasing temperature. (C) 2004 Elsevier B.V. All rights reserved.