Three-step reactive hot pressing of B4C–ZrB2 ceramics

B4C–ZrB2 ceramics were reactively hot pressed by three-step process using B and C with Zr (C–B–Zr mixtures) or ZrO2 (C–B–ZrO2 mixtures) as raw materials. Based on thermodynamic analysis and experimental results, the C–B–Zr or C–B–ZrO2 mixtures were firstly held at 1000 °C, then held at 1650 °C, and finally held at 2000 °C under 30 MPa. B4C–ZrB2 ceramics were obtained by using the three-step process and controlling the reaction sequence. The ZrB2 grains in B4C–ZrB2 ceramics from C–B–Zr mixtures had a bimodal grain size distribution including fine grains with size of 1–2 μm and large agglomeration-like grains with size of 10–30 μm, while that in the ceramics from C–B–ZrO2 mixtures showed homogeneous distribution with small grain size of 1–2 μm. The B4C–ZrB2 ceramics from C–B–ZrO2 mixtures showed higher relative density, more homogeneous and fine-grained microstructure, higher hardness (33.0 ± 1.3 GPa), and comparable toughness (4.1 ± 0.2 MPam1/2), compared with the ceramics from C–B–Zr mixtures.