Three-step reactive hot pressing of B4C–ZrB2 ceramics.

B 4 C–ZrB 2 ceramics were reactively hot pressed by three-step process using B and C with Zr (C–B–Zr mixtures) or ZrO 2 (C–B–ZrO 2 mixtures) as raw materials. Based on thermodynamic analysis and experimental results, the C–B–Zr or C–B–ZrO 2 mixtures were firstly held at 1000 °C, then held at 1650 °C, and finally held at 2000 °C under 30 MPa. B 4 C–ZrB 2 ceramics were obtained by using the three-step process and controlling the reaction sequence. The ZrB 2 grains in B 4 C–ZrB 2 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–ZrO 2 mixtures showed homogeneous distribution with small grain size of 1–2 μm. The B 4 C–ZrB 2 ceramics from C–B–ZrO 2 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 MPam 1/2 ), compared with the ceramics from C–B–Zr mixtures. [ABSTRACT FROM AUTHOR]