Effect of Mo2C addition on the mechanical properties and oxidation resistance of ZrB2-SiC ceramics

Simple hot pressing and vacuum pre-treatment at 1600 °C followed by hot pressing were used for obtaining dense composites of ZrB2–15 vol% SiC– 5 vol% Mo2C. The room temperature strength was around 820 MPa for the hot-pressed material and 650 MPa for the material obtained by use of thermally treated powders. At 1800 °C, the strength converged to 154 and 182 MPa, respectively, as was mostly driven by SiC grain sliding. Oxidation in static air at 1600 °C for 2 h showed the formation of a 3-layered scale for both materials but with different thickness. The outermost layer was a borosilicate glass; the intermediate layer consisted of a phase based on zirconium oxide, silicon oxide, molybdenum boride and oxide; and the last layer was a silicon-depleted boride matrix. The two-step processing route resulted in a material with higher oxidation resistance, due to coarser grain size and higher amount of (Mo,Zr)B phase, which remained stable as solid compound in the sub-scales. •Addition of Mo2C reduce impurities on the surface of ZrB2 ceramics and form high-temperature phases such as solid solution (Zr,Mo)C and MoB.•The vacuum treatment leads to a decrease oxygen and an increase the MoB content of composite ceramics.•The addition of molybdenum carbide to ZrB2–15 vol% SiC improves oxidation resistance at 1600 °C.