Boride-based Ultra High Temperature Ceramic Surface Coatings deposited via Controlled Atmosphere Plasma Spray

Traditional aerospace materials can no longer withstand the temperatures experienced at extreme hypersonic flight speeds, prompting a demand for new thermal protection system (TPS) surface coatings. Zirconium Boride (ZrB2) and Hafnium Boride (HfB2) are Ultra High Temperature Ceramics (UHTC) with the ideal combination of high melting temperatures and thermal conductivities which can be exploited to transfer heat rapidly away from at risk surfaces.

However, these materials have poor oxidation resistance and the inclusion of oxides within deposited coatings would detrimentally affect vital properties. In this paper, we demonstrate the successful construction and operation of a Controlled Atmosphere Plasma Spray (CAPS) vessel for the deposition of boride based UHTC materials with minimal oxide inclusions. Coatings deposited within the CAPS vessel have undergone an extensive comparison to samples deposited via traditional Atmospheric Plasma Spray (APS). Rietveld analysis was employed to inspect the amount of oxides formed within deposited coatings and nano-hardness indentation utilized to support the results. The hardness data additionally underwent a Weibull analysis that allowed a novel inspection into the variability in hardness of samples that was attributed to regions of high and low oxide inclusions.