PLASMA ASSISTED CHEMICAL VAPOR-DEPOSITION ON 3-DIMENSIONAL SUBSTRATES

A novel plasma assisted chemical vapor deposition reactor forms ceramic coatings on "three-dimensional" surfaces of complicated parts such as cutting tools and bearing surfaces. The reactor chamber features a unique rf-driven electrode configuration to establish uniform, large volume, low temperature plasmas from which the coatings are deposited. Highly adherent silicon nitride coatings formed from silane/ammonia/argon plasmas have hardness values up to 30 GPa. Variations of methane/silane feed gas ratios produce microcrystalline silicon carbide films with C/Si atomic ratios ranging from 0.4 to 3; the coatings consist of free Si and stoichiometric SiC; SiC, free Si and diamond-like carbon (DLC); or SiC and DLC, depending on the methane/silane fraction. Hardness varies monotonically between about 10 and 60 GPa as the carbon fraction increases. SiC coatings significantly reduced wear rates in abrasive wear tests; Si-SiC coatings effectively protected molybdenum samples during a 180 h oxidation test in 650-degrees-C air.