Studies on Parametric Optimization of HVOF-Sprayed Cr2O3 Coatings on Al6061 Alloy

Abstract

High-velocity oxy-fuel (HVOF) is a widely used thermal spray technique to obtain high density, high bond strength, and improved hardness coatings. In the present work, optimization of HVOF process parameters was carried out using the Taguchi method to minimize porosity and improve microhardness, and bond strength of Cr2O3 coatings. Based on the signal-to-noise ratio and analysis of variance, the significance of each process parameter and optimum parameter combination is obtained. Based on the signal-to-noise ratio, the most significant process parameter affecting porosity and microhardness was standoff distance, while for bond strength, it was powder feed rate. An optimal combination of process parameters for porosity, microhardness, and bond strength was obtained from S/N ratio analysis. For porosity, optimal parameters were standoff distance of 100 rpm, powder feed rate of 30 g/min, and gun speed of 250 mm/s. The optimal process parameters for microhardness were standoff distance of 300 rpm, powder feed rate of 50 g/min, and gun speed of 200 mm/s. Finally, for bond strength, the optimal process parameters were standoff distance of 300 rpm, powder feed rate of 50 g/min, and gun speed of 250 mm/s. Statistical results for porosity, microhardness, and bond strength showed that the difference between the predicted R2 and adjusted R2 values were relatively minimal and close to the one highlighting the fitness of the regression model employed for analysis. Fracture analysis after bond strength test showed combined adhesion/cohesion type failure for the Cr2O3 coatings.