Microstructures and properties of silicon carbide- and graphene nanoplatelet-reinforced titanium diboride composites

Monolithic TiB₂, TiB₂-SiC, and graphene nanoplatelet (GNP)-containing TiB₂–SiC-GNP composites were prepared by spark plasma sintering (SPS). The Vickers hardness and thermal conductivity values of the TiB₂-SiC composites decreased with increasing SiC addition. However, SiC addition increased the fracture toughness and oxidation resistance relative to TiB₂. The GNP-containing composites exhibited different behaviours depending on the GNP content and strength of the interface between the GNPs and surrounding matrix. A strong interface improved the oxidation resistance and thermal transfer properties. The highest fracture toughness values were achieved for the composites with 5 vol% GNPs, but the higher GNP loadings resulted in poorer mechanical properties and thermal conductivities. The formation of Si-depleted layers was also observed after oxidation at 1200–1400 °C for all composites.