Effects of SiC addition on the densification behavior and oxidation resistance of spark plasma sintered CrB₂-SiC composites

Monolithic CrB₂ and CrB₂-SiC (10, 15, 20 vol%) composites were produced by spark plasma sintering (SPS) at 1500 °C for 5 min under a pressure of 40 MPa. The densification, oxidation behavior and mechanical properties (Vickers hardness and indentation fracture toughness) of monolithic CrB₂ and CrB₂–SiC composites were investigated. No additional peaks beyond the characteristic peaks of the starting material were observed. The relative density was increased from 97.4 % to 99.1 % with the addition of 20 vol% SiC. The incorporation of SiC increased the Vickers hardness, indentation fracture toughness and oxidation resistance compared to those of monolithic CrB₂. Moreover, transgranular fracture was identified as the predominant fracture mode in both SiC-containing and SiC-free samples. It was observed that CrB₂ and CrB₂-SiC composites with furnace oxidation between 900 and 1100 °C did not contain Cr in the oxidized layer during oxidation and the protective oxide layers prevented further oxygen penetration which improved oxidation resistance. The oxidation behavior of the CrB₂-SiC binary composite demonstrated the formation of a Cr-free region, whereas the presence of Si, C and O elements in the EDS mapping indicated the formation of a silicon oxycarbide glassy phase. The oxidation resistance of CrB₂ composite with 15 vol% SiC was improved by a factor 20 compared to that of CrB₂.