Published online by Cambridge University Press: 03 March 2011
Four-point bending creep tests were conducted in air on two alumina matrix composites reinforced with 18 and 30 vol% of silicon carbide whiskers, respectively. In both materials, the SiC whiskers tended to form agglomerates. In the temperature range from 1673 to 1823 K, the stress exponents, n, were ∼3.9 and ∼6.3 and the activation energies for creep, Q, were ∼690-740 and ∼930-1010 kJ mol−1 for the composites containing 18 and 30 vol % of SiC, respectively. It is shown that the higher value of n in the composite with 30 vol % of SiC whiskers may be lowered to ∼3 by incorporating a threshold stress. The creep strength of both composites was enhanced by comparison with a similar composite containing 9.3 vol % of SiC whiskers, but there was only a very minor improvement in creep strength when the volume fraction of whiskers was increased from 18 to 30 vol %.