Effect of plasma sprayed flyash based composite coatings on corrosion resistance

With the aim of exploring the possibility of achieving a low-cost thermal spray coating to prevent wear, erosion and corrosion. In the current study, flyash-Al₂O₃ and flyash-SiC composite coatings were effectively created using the air plasma spray process on substrates of Al6061 alloy. NiCr material is used as the bond coat to improve the bond strength between the coat and the substrate. Taguchi's DoE method is applied to for spray process parameters optimization. In addition, the developed coating is subjected to microstructure analysis and long-term immersion corrosion testing (1 year) in an aqueous environment to assess corrosion properties. The results revealed that the over a certain test period, the developed flyash-SiC coating has greater corrosion resistance than the uncoated and flyash-Al₂O₃ coated Al6061. It is noticed that the corrosion resistance of the flyash-Al₂O₃ coating shifts to a negative value with respect to the uncoated substrate. The uncoated sample is extensively pitted and locally corroded, as shown by the SEM image of the corroded surface. Flyash-corroded Al₂O₃'s surface exhibits extensive degradation in the form of peeling, breaking, and cracking of the splats. With flyash-SiC composite coating a very minor corrosion splat deterioration is seen.