INFLUENCE OF WHISKER VOLUME FRACTION ON THE CREEP-BEHAVIOR OF ALUMINA COMPOSITES REINFORCED WITH SILICON-CARBIDE

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 similar to 3.9 and similar to 6.3 and the activation energies for creep, Q, were similar to 690-740 and similar to 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 similar 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%.