HVOF Thermal Spray

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HVOF stands for High-Velocity-Oxy-Fuel. The HVOF thermal spray process was originally invented in the hopes of finding an alternative to the Detonation Gun process. In this process, combustion takes place between oxygen and a fuel gas such as hydrogen, similar to the simple combustion guns, except that additionally, the velocity is highly accelerated. Thus the coating powder particles get both thermal energy as well as kinetic energy. One can visully see diamond patterns in the flame indicating the supersonic speed of the process. Powder particles are usually injected through the gun and form high quality coatings. To prevent coating build-up in the gun, thermal spray engineers have used some tricks such as changing the cooling water flows and directions. HVOF thermal spray produces dense microstructures and is very suitable to coat materials such as tungsten-carbide-cobalt, Cobalt-molybdenum,Chromium, silicon ( commonly known as T-800 ). It has also been very successfully used in re-building of mis-machined surfaces using inconel. Cobalt-Nickel-Chrome-Aluminum-Yttrium (CoNiCrAlY) deposits formed by HVOF thermal spray process using certain parameters have produced LPPS quality coatings as far as oxides and porosity are concerned. This is of course, a succint description of the HVOF process.