Effect of ZrB2 and its oxide impurities (ZrO2 and B2O3) on hot-pressed Si3N4 ceramics at low temperature

Based on the previous work on Si 3 N 4 -ZrB 2 , the addition of 2.5 vol.% ZrB 2 promoted α - to β -Si 3 N 4 phase transformation, bimodal microstructure, and toughness and strength improvement after hot-pressing at 1500 °C. However, the mechanism needed to be further explored. In the present work, the effect of ZrB 2 and its oxide impurities (ZrO 2 and B 2 O 3 ) on phase composition, microstructure and mechanical properties of Si 3 N 4 ceramics with MgO-Yb 2 O 3 additives were studied. Results showed that the addition of B 2 O 3 had no influence on Si 3 N 4 ceramics, whereas the addition of ZrO 2 inhibited the α - to β -Si 3 N 4 phase transformation, formed an uniform equiaxed microstructure, and deceased the toughness and strength. The positive effect of oxide impurities can be eliminated. Based on the STEM analysis , the possible reason was that the addition of ZrB 2 led to the formation of Si-Mg-O-N-Yb-Zr-B liquid phase , and then promoted α - to β -Si 3 N 4 phase transformation.