ZrB 2 ‐SiC and ZrB 2 ‐ZrC Ceramics with High Secondary Phase Content

Zirconium diboride–based ceramics were studied to explore the effects of high secondary phase content and the relative merits of silicon carbide and zirconium carbide. Densification and grain growth were not influenced by heating rate or composition. Hardness increased with silicon carbide or zirconium carbide content from 18 to 26GPa and 18 to 21.5GPa respectively. Flexural strength was controlled by grain size and mode of crack propagation, and maximized at 380MPa at 20wt% silicon carbide and 590 MPa at 50wt% zirconium carbide. Zirconium carbide enhanced flexural strength better, due to its smaller coefficient of thermal expansion mismatch with zirconium diboride.