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

Abstract

Based on the previous work on Si3N4-ZrB2, the addition of 2.5 vol.% ZrB2 promoted α- to β-Si3N4 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 ZrB2 and its oxide impurities (ZrO2 and B2O3) on phase composition, microstructure and mechanical properties of Si3N4 ceramics with MgO-Yb2O3 additives were studied. Results showed that the addition of B2O3 had no influence on Si3N4 ceramics, whereas the addition of ZrO2 inhibited the α- to β-Si3N4 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 ZrB2 led to the formation of Si-Mg-O-N-Yb-Zr-B liquid phase, and then promoted α- to β-Si3N4 phase transformation.