Post-processing parameter optimization to enhance the surface finish of HVOF-developed coatings

Composite coatings of titanium carbide (TiC) and chromium oxide (Cr2O3) were successfully developed on the surface of Al-6061 aluminium alloy plates using high-velocity oxy-fuel (HVOF) thermal spray technique. The surface quality tested using the surface roughness tester (SRT) showed a high surface roughness in both TiC + 10% Cr2O3 and Cr2O3 + 10%TiC coatings. The high surface roughness obtained in the coated surfaces posed a limitation in its use as both tribological and corrosion protection coatings. Post-processing of the coated surfaces was performed through hot and cold compression techniques, respectively, to reduce the surface roughness. The influencing post-processing parameters such as the thermal load, compressive load and loading time durations were optimized using the Taguchi analysis in combination with Single-Response Performance Index (SPI), to minimize the surface roughness and enhance the surface finish of the coated component. The obtained optimized levels were utilized in the post-processing of the coated samples to obtain the lowest surface roughness value. The post-processed surface roughness (Ra) was validated using the surface roughness tester. The optimization technique using Taguchi design of experiments showed that the measured and the regression equation computed values were highly similar with minimalistic deviations. The post-processing of the coated surface showed an improved surface finish by reducing the measured Ra from 19.383 µm to lowest of 3.345 µm after post-processing. The research concluded that hot compression technique provided better surface finish as compared to the cold compression technique.