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)

 

 

CVD reaction

 

 

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.