Chemical Vapor Deposition of Oxidation Resistant HfB2 + SiC Composite Coatings

Abstract

Prior testing has repeatedly shown a HfB2 + SiC composite to have oxidation resistance superior to that of HfB2 or SiC. The majority of the prior work has relied on hot pressing or hipping for fabrication. Attempts to prepare the material by chemical vapor deposition have been unsuccessful. We have recently performed computerized thermodynamic free energy minimization calculations which predict reagent concentrations for the HfCl2-CH3-SiCl3-BCl3-H2 system which should result in the codeposition of the HfB2 + SiC composite at 1200–1500 K. Coatings of HfB2 + SiC offer potential for oxidation protection of graphite and carbon-carbon composites.