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

Abstract

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.The present study investigates the effect of various geometric parameters of a dual-stage thermal spray system by developing a comprehensive mathematical model. The objective is to develop a predictive understanding of various design parameters. Conservation of mass, momentum and energy of reacting gases were taken into account in developing the model. Due to low particle loading, the particle phase was decoupled from the gas phase. The results demonstrate the advantage of dual stage system over single stage system especially for the deposition of temperature sensitive materials.