HVOF (High Velocity Oxygen Fuel).

HVOF is a high-velocity flame spray process.  A mixture of fuel and oxygen is fed into a combustion chamber, where they are ignited and combusted continuously.  The resultant hot gas exits at a pressure close to 1 mpa and the jet velocity at the exit of the barrel exceeds the speed of sound.

The resulting coating has low porosity, high bond strength and is typically used to deposit wear and corrosion resistance coatings.