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High Velocity Oxygen Fuel Spray (HVOF)

Wear- and corrosion-resistant surfaces are needed to protect critical components in various industries. The High Velocity Oxygen Fuel (HVOF) process supplies this protection by producing very dense, hard coatings with fine microstructures.

Process description

High Velocity Oxygen Fuel (HVOF) spraying uses oxygen and fuel to form a combustible mixture. Liquid-fuel HVOF (HVOF-LF) generally uses liquid kerosene as the fuel. Gas-fuel HVOF (HVOF-GF) employs fuel gases such as propylene, propane, hydrogen, or natural gas (methane).

The fuel is thoroughly mixed with oxygen within the gun and the mixture, combusted and then ejected through a nozzle at supersonic velocities. The feedstock material, in powdered form, is fed through the gun, generally using nitrogen as a carrier gas. The ignited gases surround and uniformly heat the powder material as it exits the gun and is propelled onto the workpiece surface. 

As a result of the high kinetic energy transferred to the powder particles the feedstock powder material generally does not need to be fully melted. The resulting coating has a very predictable chemistry that is homogeneous and has a fine granular structure. 

Process basics

  • Heat source: combustion 
  • Feedstock: powder (metals, alloys, carbides) 
  • Flame temperature: approx. 2 800 °C (5 000 °F) 
  • Particle velocity: 400 to 800 m/s (1 300 to 2 600 ft/s) 
  • Approximate application rate: 40 to 200 g/min (5 to 26 lb/h) 

HVOF Coatings: Characteristics and Materials

By utilizing a high-velocity stream of gas, along with a powdered coating material, the HVOF spraying process creates a dense, tightly adherent coating layer on surfaces, i.e. HVOF coatings. HVOF coatings have exceptional mechanical properties, such as high hardness, wear resistance, and corrosion resistance. Industries ranging from aerospace to automotive utilize HVOF coatings to protect critical components subjected to harsh environments.

Notably, the versatility of HVOF coating extends to various coating materials, including metallic powders such as tungsten carbide and chromium carbide, ceramic powders like alumina and zirconia, carbide powders offering exceptional hardness, and even thermal barrier coatings (TBCs) for high-temperature applications. These materials are selected based on the specific application requirements, ensuring tailored properties and optimal performance for diverse engineering components.

Key benefits of High Velocity Oxygen Fuel Spray

  • Produces coatings that are very clean, very hard and dense with fine, homogeneous structures
  • Coatings are tenaciously bonded to the substrate
  • Using liquid fuel allows compressive coating stress, using gas fuel generally allows spraying of thicker coatings

Typical applications for HVOF Spray

  • Oil & gas gate valves and seats
  • Hydroturbine components
  • Paper manufaturing rolls
  • Aircraft landing gears