Spark-plasma sintering of ZrB2 ultra-high-temperature ceramics at lower temperature via nanoscale crystal refinement

We have explored the feasibility of reducing the spark-plasma-sintering (SPS) temperature of additive-free ZrB2 ultra-high-temperature ceramics (UHTCs) via crystal size refinement of the starting powder down to the low nanoscale. We found that under otherwise the same SPS conditions (75 MPa pressure, and 100 °C/min heating ramp) nanoscale ZrB2 can be densified at temperatures about 450 °C lower than for the typical micrometre and submicrometre ZrB2 powders, and at least 250 °C below the ultra-fine powder temperature. Furthermore, the nanoscale crystal refinement also promotes the production of fine-grained ZrB2 UHTCs. We also found that elimination of the B2O3 impurities plays an important role in the complete densification. The unequalled sinterability of the nanoscale ZrB2 powders highlights the need to use high-energy ball-milling for the comminution of the typical commercially available ZrB2 powders.