Investigation of a dual-stage high velocity oxygen fuel thermal spray system

The high velocity oxygen fuel (HVOF) thermal spray coatings are used to protect the surfaces from deterioration. The base material surface properties can be modified to achieve the longevity of the product. Besides spraying material, the coating quality depends greatly on the gas and particle dynamics. The coating quality is also affected by the particle temperature, particularly for the materials which are temperature sensitive such as titanium and copper. As the gas phase temperature is high, the material gets melted and oxidized before it reaches the substrate. To avoid this problem, a dual-stage thermal spray system, has been developed for coating temperature sensitive materials. This process involves making coatings by high velocity impact of powder particles heated to temperatures below their melting point. The advantages of a dual-stage thermal spray process include an easy control of particle oxidation and production of various coating structures by controlling the particle velocity and temperature. The particle temperature can be controlled by varying the coolant flow rate in the mixing chamber.