Improved processing and oxidation-resistance of ZrB2 ultra-high temperature ceramics containing SiC nanodispersoids

We have studied the hot-pressing behavior of ZrB2/SiC ultra-high temperature ceramics (UHTCs) as a function of: (i) SiC starting-powder size, (ii) SiC vol%, (iii) ZrO2 doping, and (iv) colloidal dispersion of ZrB2/SiC powder mixtures. It has been found that the addition of SiC promotes densification of ZrB2 at a moderate hot-pressing temperature of 1650 °C. It has also been found that ball-milling of the ZrB2/SiC starting-powder mixtures using ZrO2 balls media results in the doping of the powder mixture with ZrO2, which promotes hot-pressing densification. Reduction in the SiC starting-powder size, and colloidal dispersion of the powders, both have been found to promote hot-pressing densification of ZrB2/SiC materials; the highest density achieved in such ZrB2/SiC ceramics is 99.9%. Detailed microstructural characterization of the ZrB2/SiC ceramics using electron microscopy shows that some of these materials contain a Zr(O,B)2 phase, and amorphous films at interphase interfaces. Oxidation studies reveal that SiC grain-size reduction results in improved oxidation-resistance in ZrB2/SiC materials. The ZrB2/SiC ceramics produced here possess modest hardness and toughness properties. The results presented here point to a new strategy for improving processing and oxidation-resistance of ZrB2/SiC materials: dispersion and reduction of SiC grains.