Daniel F. Carroll

Self-Reinforced Silicon Nitride — A new Microengineered Ceramic

A low cost, high fracture toughness silicon nitride material can be obtained through the in-situ growth of whisker-like elongated grains. This ability to form a reinforced material in-situ during densification avoids the processing difficulties and potential health hazards generally associated with whisker reinforced ceramic composites. The in-situ growth of elongated silicon nitride grains is controlled by the glass phase chemistry and processing conditions. A new class of self-reinforced silicon nitride materials have been developed based upon the Si3N4-Y2O3-MgO-CaO system, where yttrium can be replaced by seven other elements, magnesium can be replaced by six other elements and calcium with 19 other elements. These compositions have been found to yield fine grained, high aspect ratio silicon nitride ceramics with a unique combination of high flexure strength and fracture toughness.