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

Simple hot pressing and vacuum pre-treatment at 1600 degrees 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 degrees C, the strength converged to 154 and 182 MPa, respectively, as was mostly driven by SiC grain sliding. Oxidation in static air at 1600 degrees 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. (C) 2021 Elsevier B.V. All rights reserved.