Influence of ZrB₂ on Si₃N₄ ceramics prepared by Si nitridation and hot-pressing process

This work investigated the effect of ZrB2 content on phase composition, relative density, microstructure, and mechanical performance of Si3N4 ceramics prepared by Si nitridation and hot-pressing method. Si3N4 ceramics were fabricated using Si powder by nitridation and hot-pressing process. Results showed that the addition of ZrB2 enhanced the transformation of alpha-Si3N4 into beta-Si3N4 phase during nitridation, resulting in a greater fraction of beta-Si3N4 (above 90 wt.%) phase in Si3N4 ceramics with ZrB2 after hot-pressing. In contrast, ceramics without ZrB2 had a lower ratio of beta-Si3N4 (40.4 wt.%). The use of 2.5 vol.% ZrB2 yielded a significant bimodal microstructure and increased fracture toughness to 5.0 +/- 0.2 MPam(1/2), but decreased Vickers hardness to 16.4 +/- 0.5 GPa. However, increasing the ZrB2 content to 5 vol.% and 10 vol.% led to a massive formation of equiaxed coarse beta-Si3N4 grains and a significant decrease in Vickers hardness and fracture toughness.