Understanding the Effects of Processing on the Mechanical Behavior of a SI3N4 Ceramic Through Microstructural Investigations

The mechanical properties of silicon nitride (Si3N4) ceramics are determined by their microstructure, which in turn depends on processing routes adopted to fabricate the material. To obtain dense Si3N4, sintering aids are almost always added during the densification process. The sintering aids remain in the ceramics as amorphous residues which adversely affect the high temperature mechanical behavior of the material. In this paper, we have investigated the effects of processing on the mechanical behavior of a sintered Si3N4 ceramic through detailed microstructural observations. A commercial Si3N4 was annealed using conventional furnace annealing and microwave annealing at different temperatures. Creep tests were performed to compare the high temperature mechanical behavior of the as-sintered and annealed ceramics. It was found that microwave and furnace annealing heat-treatments improve the creep resistance of the ceramic through devitrification of the triple junctions phases.