Optimizing HVOF spray process parameters to attain minimum porosity and maximum hardness in WC–10Co–4Cr coatings

• Empirical relationships were developed to estimate porosity and hardness.
• Response surface methodology (RSM) was applied to optimize HVOF spray parameters.
• The coating exhibits a minimum porosity of 1.38 vol.% and maximum hardness of 1318 HV.
• Porosity affects the coating hardness and shows inversely proportional relationship.
• Oxygen flow rate dominates the coating porosity and hardness.

Many thermal and thermo-chemical surface treatment techniques are being used to modify the surface of the material with desired properties for various applications in service. Nowadays, high velocity oxy-fuel (HVOF) spray is being widely used in industrial applications due to its ability to produce a high-quality coating with required hardness and low oxide content due to its high velocity impact inherent in the process. Porosity and hardness are two important coating properties for wear and corrosion related applications, and they play a significant role in the service life of the components. In HVOF spraying, the parameters such as oxygen flow rate, liquefied petroleum gas (LPG) flow rate, powder feed rate and spray distance have greater influence on the final properties of the coatings. The present work aims to select the optimum HVOF spray parameters to attain minimum porosity and maximum hardness in WC–10Co–4Cr coating sprayed on naval brass substrate material. Statistical tools such as design of experiments (DOE), analysis of variance and response surface methodology (RSM) were used to meet the stated objectives. From the results, it was observed that the oxygen flow rate has greater influence on coating porosity and hardness followed by LPG flow rate, powder feed rate and spray distance, respectively.