Microstructure and Mechanical Properties of ZrB2-HfC Ceramics Influenced by HfC Addition

ZrB2-HfC ceramics have been fabricated using the liquid phase sintering technique at a sintering temperature as low as 1750 degrees C through the addition of Ni. The effects of HfC addition on the microstructure and mechanical properties of ZrB2-based ceramics have been investigated. These ceramics were composed of ZrB2, HfC, Ni, and a small amount of possible (Zr, Hf)B-2 solid solution. Small HfC grains were distributed among ZrB2 grain boundaries. These small grains could improve the density of ZrB2-based ceramics and play a pinning role. With HfC content increasing from 10 wt % to 30 wt %, more HfC grains were distributed among ZrB2 grain boundaries, leading to weaker interface bonding among HfC grains; the relative density and Vickers hardness increased, and flexural strength and fracture toughness decreased. The weak interface bonding for 20 and 30 wt % HfC contents was the main cause of the decrease in both flexural strength and fracture toughness.