SPHERICAL-IMPACT DAMAGE AND STRENGTH DEGRADATION IN SI3N4-SIC COMPOSITES

Four types of SiC-whisker/silicon nitride and SiC-particle/silicon nitride composites were produced, and their mechanical properties and impact damage behaviour examined. All of the composites exhibited elastic response behaviour at spherical impact with Hertz cone crack initiation. Impact resistance behaviour, however, was different for each composite. This was due to the different mechanical properties produced by their microstructures. A SiC-platelet/silicon nitride composite displayed the highest resistance to crack initiation and propagation, which resulted in high impact resistance to strength degradation. On the other hand, SiC-particle/silicon nitride, SiC-whisker/silicon nitride, and large SiC-whisker/silicon nitride composites showed less impact resistance, even though they have higher mechanical properties such as bending strength and fracture toughness. © 1990 Chapman and Hall Ltd.