Electrodeposition of Ni-Al2O3 composite coatings employing supercritical CO2 baths

• Ni-Al2O3 composite coating could be fabricated by electrodeposition using an sc-CO2 bath.
• A smoother surface of the Ni-Al2O3 composite coating was obtained.
• Improved hardness and wear resistance were attributed to electrochemical carburization.
• Ni-Al2O3 coating had a higher corrosion resistance if prepared from the sc-CO2 bath.

The co-deposition of Ni and Al2O3 by electrodeposition in supercritical CO2 (sc-CO2) baths with and without emulsification was studied. The material characteristics of the Ni-Al2O3 composite coatings, including its crystal structure, surface morphology, chemical composition, micro-hardness, wear resistance, and corrosion resistance, were all examined and compared with those of pure deposited Ni. Although a reduction in electrodeposition rate and a lower solid Al2O3 particle content in the composite coatings were obtained incorporating sc-CO2 bath, substantial increases in the micro-hardness and wear resistance of the coatings were observed comparing with those formed in conventional bath. The advantages of sc-CO2 electrodeposition, with and without surfactant addition, over the conventional electrodeposition of composite coatings, are addressed.