Hf-based thick refractory coatings will be developed on existing carbon substrates including C-C composites to improve its oxidation resistance at 3200-5000F. A wet-chemical synthesis approach to preparing HfB2VC mixtures will be used, ideally lending itself to control the HfB2VC mixtures and to afford a graded coating with a carbon rich inner-coat, and a HfB2 rich outer coat. A HfO2 outer layer will be deposited on the composite. A dense tetragonal-stabilized HfO2 over coat will provide more protection. Elements of stabilization include tungsten (W), molybdenum (Mo), and yttrium (Y). Furthermore, W and Mo will also serve as an in-situ sintering aid for HfO2. The HfB2 phase will provide supplementary protection if any failure should occur in the original HfO2 outer layer. Samples will be tested by the use of an oxyacetylene torch test to evaluate temperatures to 5000F. Successful tests will include samples that are able to withstand multiple thermal cycles without cracking and have low erosion depths.
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