Fundamental understanding on the microstructure and corrosion resistance of Cr-(Cr, Al)(2)O-3 composite coatings in-situ synthetized by reactive plasma spraying

Three composite coatings were prepared with Al-Cr2O3-Al2O3 composite powders feedstocks by in-situ reactive plasma spraying, and the microstructures and corrosion resistances were studied. The results show that the CAC-1 coating is the hypoeutectic microstructure consisting of large-size Cr particles and the eutectic structure, the CAC-2 coating presents a typical eutectic microstructure [nano-Cr + (Cr, Al)(2)O-3], and the CAC-3 coating is the hypereutectic microstructure which is composed of (Cr, Al)(2)O-3 solid solution and eutectic structure. The corrosion resistance of the coating is closely related to the microstructure and defects of the coating. The surface of the nano-Cr particles in the CAC-2 coating can form a stable Cr(OH)(3) film, which hinders the further contact with the electrolyte, thereby improving the corrosion resistance of the coating itself. In addition, the uniform and dense microstructure also leads to the least coating defects, further improving the corrosion resistance of the coating. While the surface product film of large-size Cr particles in the CAC-1 coating cannot exist stably, causing the Cr to continue to dissolve until it peels off. The coating itself has the highest porosity, so the coating has the worst corrosion resistance. The CAC-3 coating mainly exhibits the characteristics of ceramic coating due to the limited eutectic structure contained. Due to the unevenness of the microstructure, the coating has more defects, resulting in lower corrosion resistance than the CAC-2 coating.

Automated summary

The corrosion resistance of the three composite coatings is closely related to their microstructures and defects. The CAC-2 coating with uniform and dense microstructure exhibits the best corrosion resistance, while the CAC-1 coating with large-size Cr particles and high porosity has the worst corrosion resistance. The CAC-3 coating, characterized by uneven microstructure, shows lower corrosion resistance compared to the CAC-2 coating.