Properties of whisker-reinforced ceramics

The paper summarizes the findings of a series of studies of SiC whisker-reinforced alumina composites emphasizing the properties of these composites and the influence of composition and microstructure. First, both the steady-state toughness and the R-curve response increase with whisker content and diameter. The room temperature flexure strength of aluminas with different grain sizes also increases with whisker content. Furthermore, the resistance to slow crack growth under both montonic and cyclic loading is substantially improved by whisker reinforcement in comparison to that of alumina and other ceramics. The thermal conductivity and electrical resistivity exhibit a substantial increase and decrease, respectively, with whisker loadings above 10 vol.%. The thermal expansion coefficients decrease in a systematic fashion with increase in whisker content. However, the expansion coefficients are greater in the direction parallel to the hot pressing axis as compared to the perpendicular direction due to internal stresses and the preferred orientation of whiskers. The changes in mechanical and thermal properties due to SiC whisker additions result in substantial improvement in thermal shock resistance for samples of various sizes. At elevated temperatures, tests in air show that improvements in strength and resistance to strength degradation are associated with SiC whisker reinforcement. The limitingmore » factors in elevated temperature mechanical response of the composite at 1200{degrees}C and above are related to surface oxidation-reaction processes and creep. On the other hand, the creep resistance of the composite is far greater than alumina with a similar fine grain size at temperatures {ge} 1200{degrees}C. Futhermore by increasing the grain size of the alumina matrix, the creep resistance of the composite can be substantially increased.« less