Reactively sputter-deposited high-emissivity tungsten carbide/carbon coatings

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Abstract
Stable adherent high-emissivity tungsten carbide/carbon coatings have been deposited onto iridium and carbon/carbon substrates by reactively sputtering a cemented tungsten carbide target in an acetylene–argon atmosphere. The thin, light-weight, high-emissivity coatings have potential for improving the heat transfer characteristics and reducing the weight of satellite thermoelectric generators. The tungsten carbide/carbon coating emissivity increased from 0.35–0.91 as the acetylene partial pressure during deposition increased from 0–0.133 Pa. Auger electron spectroscopy, x-ray diffraction, and electron microprobe analysis of the coatings revealed that the film structure and composition changed from β-WC1-x to an amorphous carbon-rich material as the acetylene partial pressure exceeded 0.034 Pa. One-micron-thick tungsten carbide/carbon films on iridium withstood vacuum anneals at 1775 K for 19 h without significant degradation in the coating durability or emissivity.

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