Microstructure and densification of ZrB₂-SiC composites prepared by spark plasma sintering

ZrB₂-SiC composites were prepared by spark plasma sintering (SPS) at temperatures of 1800-2100 °C for 180-300 s under a pressure of 20 MPa and at higher temperatures of above 2100 °C without a holding time under 10 MPa. Densification, microstructure and mechanical properties of ZrB₂-SiC composites were investigated. Fully dense ZrB₂-SiC composites containing 20-60 mass% SiC with a relative density of more than 99% were obtained at 2000 and 2100 °C for 180 s. Below 2120 °C, microstructures consisted of equiaxed ZrB₂ grains with a size of 2-5 μm and α-SiC grains with a size of 2-4 μm. Morphological change from equiaxed to elongated α-SiC grains was observed at higher temperatures. Vickers hardness of ZrB₂-SiC composites increased with increasing sintering temperature and SiC content up to 60 mass%, and ZrB₂-SiC composite containing 60 mass% SiC sintered at 2100 °C for 180 s had the highest value of 26.8 GPa. The highest fracture toughness was observed for ZrB₂-SiC composites containing 50 mass% SiC independent of sintering temperatures.