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HVOF Coating Process Overview

The principle for HVOF is that high-volume combustible gases are fed into a combustion chamber. The combustion takes place internally at very high chamber pressures. It is then fed into a long confining nozzle or barrel through which the combusting gases exit the device generating a supersonic gas jet with very high particle speeds. The sheer volume of gas flow, coupled with the high temperature of combustion, creates gas velocities in the 1525 to 1825 m/s (5000 to 6000 ft/s) range at the nozzle exit. The combustion jet temperatures ranges between 2500 to 3100 °C (4500 to 5600 °F). High-velocity oxyfuel gases used include hydrogen, propylene, propane, acetylene, and kerosene etc. The process results in extremely dense, well bonded coatings, making it attractive for many applications. The high gas velocity generated by HVOF, much higher than in conventional flame or plasma spray, has been shown to increase particle velocity, with a corresponding increase in coating density and coating adhesion.
HVOF Coating Process Overview

Components of HVOF System

  • Oxygen, fuel gas, and powder carrier gas circuits consisting of a high-volume gas supply, high-pressure gas hoses, high flow gas regulators for oxygen and fuel, high flow gas controls, and flashback arrestors at the gun and regulators
  • An HVOF spray gun comprising a torch body, combustion chamber, powder injector, and nozzle
  • Water- or air-cooling circuits
  • Feedstock delivery: high-pressure powder feeder
  • Safety interlocks and console purging

Coating Characteristics

High-velocity oxyfuel coating properties are reported to be comparable to those of detonation gun coatings, particularly for carbide and oxide coatings. High Velocity Oxyfuel sprayed coating density, adhesion, and oxide contents also compare favorably with high-energy, plasma sprayed coatings. Porosity is typically reported at less than 1%. Compositional analysis of HVOF WC/Co coatings have shown that, compared to plasma spray, only a small amount of WC decomposition (to W2C) occurs, preserving the intrinsic high hardness values of the material.

Benefits

  • Fine microstructure
  • Very dense and low porous coatings
  • High bond strength
  • Finishes to an extremely smooth surface
  • Optimal microhardness
  • Excellent corrosion properties
  • Excellent for hard metal (carbide coatings)
  • Low degree of oxidation

Typical Coatings

  • Cermets, carbides (tungsten carbide, chromium carbide)
  • Super alloys based on iron, nickel, and/or cobalt (Stellite, Triballoy, Inconel, Hastelloy, etc.)
  • Hard Chrome Replacement
  • MCrAlYs bond coatings under TBCs (Thermal Barrier Coatings)

Applications

  • Sealing moving surfaces to prevent seals from leaking
  • Improvement of wear resistance and chemical protection of ball valves
  • Protection of hydraulic piston rods against seawater environment in the offshore industry
  • Repairs and dimension corrections of worn drive shafts and bearing seatings
  • Substrate for Thermal Barrier Coatings (TBCs)
  • Cavitation protection in hydroelectric power stations
  • Protection of pump casings and impellers against chemical corrosion
We, at Metal Coat started our journey way back in 1988 are one of the leading manufacturers and suppliers of a vast array of Thermal Spray Equipment and Coating Systems.
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