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 halide (g) → metal(s) + byproduct (g)
metal halide (g) + oxygen/carbon/nitrogen/boron source (g) → ceramic(s) + byproduct (g)
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
|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|
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 CVD rhenium thrust chambers for tactical propulsion applications.
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.