Microstructural features and properties of the nano-crystalline SiC/BN(C) composite ceramic prepared from the mechanically alloyed SiBCN powder

► As-milled SiBCN powder consists of spherical agglomerates, 6.5±5.4μm in size. ► Hot pressed SiC/BN(C) ceramic consists of nano β-SiC, α-SiC and BN(C). ► Turbostratic BN(C) is composed of t-carbon, t-BN and B-doped t-carbon layers. ► BN(C) retards grain growth and is responsible for the fine grains. ► The temperature and pressure greatly affect the ceramic density and properties. Nano SiC/BN(C) ceramic was prepared from the mechanically-alloyed amorphous SiBCN powder, hot pressed at 1900°C under 80MPa in the nitrogen atmosphere for 30min. The microstructures and the properties of the prepared ceramic were carefully studied by XRD, TEM (SAED, HRTEM and EFTEM), EELS and property testing. Results show that the ceramic consists of β-SiC, α-SiC and BN(C). SiC has an average grain size of about 78.2±32.4nm, most of which have numerous stacking faults. BN(C) has small size, no fixed shape and turbostratic structure with heterogeneously distributed t-carbon layers, t-BN layers and B-doped t-carbon layers. It has uniform distribution in the ceramic, retarding the atomic diffusion and being responsible for the fine grains. The ceramic has room-temperature density, flexural strength, Young’s modulus and fracture toughness of 2.6g/cm3, 331.1MPa, 139.4GPa and 2.8MPam1/2, respectively. The detailed investigation of the hot-pressed SiC/BN(C) ceramic is helpful for the further study of this material and other ceramics, targeted for the high-temperature applications.