Processing and Properties of (Zr,Hf)B_2-SiC Ceramic Composites

摘要

Different molar ratio of HfB_2 and ZrB_2 had been mixed, and 30 vol.% SiC was selected as sintering additives. The mixing powders were sintered by hot pressing at 1900 °C for 1 h under a pressure of 20 MPa in Ar atmosphere. X-ray diffraction, scanning microscopy and Archimedes's method were used to characterize the phase, microstructure and density of the sintered composites. Meanwhile, the hardness, the fracture toughness and flexural strength of the obtained composites were considered too. It can be found that the (Zr,Hf)B_2 solid solutions were formed by HfB_2 and ZrB_2 during the sintering. The flexural strength of (Zr,Hf)B_2-SiC composites increased with the amount of HfB_2 increasing, which reached (332±40) MPa for the composites content of 70% HfB_2. Which fracture toughness was (2.22±0.25) MPa·m~(1/2). The highest Vickers' harness of was (24.8±3.4) GPa for the composites content of 50% HfB_2.