Effect of Oxygen/Fuel Ratio on the Tribological Properties of HVOLF Thermal Spray WC-12Co Coatings

Abstract

This project investigated the application of the WC-12Co coatings to stainless substrates utilising the HVOF approach. The variables in the coating method were the fuel and oxygen flow rates. The observed properties were the tribology performance, hardness level, surface roughness, porosity level and coating thickness. The samples for investigation were prepared in the lab utilising cutting, mounting and polishing stages. It was shown that the HVOF approach is considered an efficient and compatible approach to apply the WC-12Co coating on stainless substrates. Moreover, it was observed that the HVOF approach is sensitive with regards to the various parameters in particular the oxygen-to-fuel ratio as it affects the melting and fusion of the coating layer. The optimum parameters obtained in this project were a fuel and oxygen rates of 380 ml/min and 944 l/min, receptively, at a Stand-of-Distance (SoD) value of 386 mm with 25 passes over the surface. The obtained results showed that as the hardness increases, the coefficient of friction and surface irregularities decrease. Also, at a given oxygen rate, as the fuel rate increases, the hardness increases. On the contrary, at a given fuel rate, as the oxygen rate increases, the hardness decreases. This project presented an optimisation study whereby the optimum parameters for the HVOF were identified based on physical and mechanical testing.