Densification of ZrB 2-based composites and their mechanical and physical properties: A review

Abstract

This study reviews densification behaviour, mechanical properties, thermal, and electrical conductivities of the ZrB 2 ceramics and ZrB 2-based composites. Hot-pressing is the most commonly used densification method for the ZrB 2-based ceramics in historic studies. Recently, pressureless sintering, reactive hot pressing, and spark plasma sintering are being developed. Compositions with added carbides and disilicides displayed significant improvement of densification and made pressureless sintering possible at ≤2000 °C. Reactive hot-pressing allows in situ synthesizing and densifying of ZrB 2-based composites. Spark plasma sintering displays a potential and attractive way to densify the ZrB 2 ceramics and ZrB 2-based composites without any additive. Young's modulus can be described by a mixture rule and it decreased with porosity. Fracture toughness displayed in the ZrB 2-based composites is in the range of 2–6 MPa m 1/2. Fine-grained ZrB 2 ceramics had strengths of a few hundred MPa, which increased with the additions of SiC and MoSi 2. The small second phase size and uniform distribution led to higher strengths. The addition of nano-sized SiC particles imparts a better oxidation resistance and improves the strength of post-oxidized ZrB 2-based ceramics. In addition, the ZrB 2-based composites showed high thermal and electrical conductivities, which decreased with temperature. These conductivities are sensitive to composition, microstructure and intergranular phase. The unique combinations of mechanical and physical properties make the ZrB 2-based composites attractive candidates for high-temperature thermomechanical structural applications.