Effects of Y2O3 on microstructure and mechanical properties of ZrB2–SiC ceramics

Hot-pressed ZrB2–SiC ceramics was hot-pressed at a temperature of 1900 °C, and yttria (Y2O3) was added as a sintering aid. The amount of Y2O3 that was added had a significant influence on the sinterability and mechanical properties of the ZrB2–SiC ceramics. When a small amount (3 vol.%) of Y2O3 was added, the Y2O3 reacted with impurities oxides (ZrO2, B2O3 and SiO2) that were present on the surface of the starting powder. The elimination of impurities oxides suppressed the grain growth effectively, which led to an improvement in the densification of ZrB2–SiC ceramics. The mechanical properties, both the flexural strength and fracture toughness were enhanced through these improvements in the sinterability and microstructure. On the other hand, when a large amount (8 vol.%) of Y2O3 was added, the mechanical properties were not improved much, presumably because the extra additive made redundant liquid phase at the grain boundaries.