HVOF
A mixture of gaseous or liquid fuel and oxygen is fed into a combustion chamber, where they are ignited and combusted continuously. The resultant hot gas at a pressure close to 1 MPa emanates through a converging-diverging nozzle and travels through a straight section. The jet velocity at the exit of the barrel (>1000 m/s) exceeds the speed of sound. A powder feed stock is injected into the gas stream, which accelerates the powder up to 800 m/s. The powder partially melts in the stream, and deposits upon the substrate.
- Fuel: propane, propylene, acetylene, hydrogen, kerosene
- Coating material: powder form
Advantage
- High coating density : similar to detonation or LPPS
- High bond strength
- Low oxide
- Compressive residual stress in the coating layer
Disadvantage
- Difficult for ceramics having high melting point
Applications
- Metal coating: Ni-base, Co-base, MCrAlY
- Cermet coating: W-carbide, Cr-carbide
