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 degrees C for 180-300 s under a pressure of 20 MPa and at higher temperatures of above 2100 degrees 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 degrees C for 180 s. Below 2120 degrees C, microstructures consisted of equiaxed ZrB2 grains with a size of 2-5 mu m and alpha-SiC grains with a size of 2-4 mu m. Morphological change from equiaxed to elongated alpha-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 degrees 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. (C) 2009 Elsevier Ltd. All rights reserved.