Chemical Vapor Deposition
Chemical vapor deposition (CVD) results from the chemical reaction of gaseous precursor(s) at a heated substrate to yield a fully dense deposit. Ultramet uses CVD to apply refractory metals and ceramics as thin coatings on various substrates and to produce freestanding thick-walled structures.
Thermodynamics and kinetics drive both precursor generation and decomposition. Control of thermodynamics and kinetics through temperature, pressure, and concentrations yields the desired deposit.
Metal deposition
metal halide (g) → metal(s) + byproduct (g) |
Ceramic deposition
metal halide (g) + oxygen/carbon/nitrogen/boron source (g) → ceramic(s) + byproduct (g) |
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Hot-wall CVD reactor rig at Ultramet |
Cold-wall CVD reactor in process |
Advantages of CVD
- Can be used for a wide range of metals and ceramics
- Can be used for coatings or freestanding structures
- Fabricates net or near-net complex shapes
- Is self-cleaning—extremely high purity deposits (>99.995% purity)
- Conforms homogeneously to contours of substrate surface
- Has near-theoretical as-deposited density
- Has controllable thickness and morphology
- Forms alloys
- Infiltrates fiber preforms and foam structures
- Coats internal passages with high length-to-diameter ratios
- Can simultaneously coat multiple components
- Coats powders
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| Layered CVD ceramic coating (top) conforms closely to underlying substrate to create a robust bond at the interface. | Microstructure of high-emittance black rhenium coating showing pyramidal dendrites formed by CVD |
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Left, large freestanding solid rhenium thruster (19" high × 10" diameter at base) fabricated by CVD, demonstrating Ultramet’s scale-up expertise; top right, freestanding parts of solid rhenium, tantalum, and tungsten formed by CVD; bottom right, monolithic rhenium thrust chambers in production at Ultramet for tactical propulsion applications.
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Top left, mirror fabricated entirely by CVD of silicon carbide foam with a polished silicon carbide facesheet; bottom left, rhenium-coated graphite spheres; right, iridium-lined rhenium thrust chamber with niobium flanges, all fabricated by CVD.