Pressureless sintering of zirconium diboride with carbon and boron carbide nanopowder

Zirconium diboride ceramics with and without carbon and boron carbide nanopowder additives were prepared by ball milling with ZrB2 grinding media and pressureless sintering. Additions of up to 1 wt% nano-B4C and 0.5 wt% C were made to the ZrB2 powder. The materials were then sintered between 1800 and 2300 °C for between 90 and 360 min in an Ar/10H2 atmosphere. After sintering at 2200 °C for 90 min, densities ranged from 88.3 to 90.7% for the ZrB2 with 0–1.0% nano-B4C addition. Carbon additions of 0.5 wt% and nano-B4C additions from 0 to 1.0 wt% resulted in densities ranging from 90.9 to 91.9% after sintering at 2100 °C for 90 min. Grain size ranged from 16.6 to 21.7 μm for ZrB2 with nano-B4C content increasing from 0 to 1.0 wt%, sintered at 2200 °C. For the ZrB2 with 0.5 wt% C, increasing the nano-B4C content from 0 to 1.0 wt% resulted in a decrease in grain size from 25.4 to 18.5 μm. The densities achieved in this study were lower than previous pressureless sintering studies of ZrB2 that used WC-6Co grinding media, presumably due to the absence of WC and Co that can also act as sintering aids.