Sintering and Toughening of Silicon Nitride-Based Composites
The properties of silicon nitride based ceramics, particularly at high temperatures, are controlled by secondary intergranular phases, normally glassy, which are present as a result of sintering additives. Properties of the sintered product can be improved by post-sintering heat treatments to crystallise the grain boundary glass. Second-phase reinforcements, such as SiC platelets or whiskers, offer further possibilities for improvements in properties and this paper describes sintering studies of silicon nitride with SiC inclusions, densified with mixed oxide additives such as Y2O3 + Al2O3. Densities as high as the matrix can be achieved by pressureless sintering with 10% platelets. SiC platelets allow increases in toughness not shown by whisker reinforcements. Toughening mechanisms involve crack deflection around the platelets.
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