Effect of LiYO(2) addition on sintering behavior and indentation properties of silicon nitride ceramics
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The influence of the sintering additive LiYO(2) (5-15 wt.%) on sintering behavior, microstructure and mechanical properties of Si(3)N(4) ceramics was investigated. Since LiYO(2) enables densification of Si(3)N(4) at extraordinarily low temperatures, sintering was carried out in the range from 1200-1700 degrees C. Densification was found to be enhanced with increasing additive content due to an increasing volume fraction of the liquid. The phase transformation and grain growth occurred through a solution-reprecipitation mechanism, where the precipitation took place preferentially on pre-existing beta-Si(3)N(4) nuclei (of which the starting powder already contained 20 wt.%). The indentation fracture toughness increased with both sintering time and additive content as a result of the growth of elongated grains.