Nanocrystalline Co-Ni alloy coating produced with supercritical carbon dioxide assisted electrodeposition with excellent wear and corrosion resistance

• Co-Ni alloy coatings are fabricated by supercritical carbon dioxide assisted electrodeposition.
• Effect of Sc-CO2 fluid on the microstructure and properties of Co-Ni alloy coatings are studied.
• Co-Ni alloy coatings produced in emulsified Sc-CO2 bath exhibit brighter, smoother surface and higher microhardness.
• Co-Ni alloy coatings prepared in emulsified Sc-CO2 bath possesses better wear and corrosion resistance.

Co-Ni alloy coatings were produced by two different electrodeposition techniques, i.e., supercritical carbon dioxide (Sc-CO2) assisted electrodeposition and conventional electrodeposition in air. Effect of the two electrodeposition techniques on surface morphology, grain size, crystalline texture, microhardness, wear and corrosion resistance of the resulting Co-Ni alloy coatings were investigated. The results show that the Co-Ni alloy coating electroplated with the aid of Sc-CO2 fluid exhibits brighter surface appearance, lower surface roughness and smaller grain size. The preferred orientation plane of (1 0 0) for the coating prepared in air is changed to be close-packed (1 1 1) facets for the coating produced in emulsified Sc-CO2 bath. The microhardness of the Co-Ni alloy coating deposited in emulsified Sc-CO2 bath is much higher than that of the one produced by the traditional electrodeposition. Moreover, the Co-Ni alloy coating produced in emulsified Sc-CO2 bath possesses better wear and corrosion resistance, which wear and corrosion rate are respectively about one fourth and half of the one deposited by the conventional electrodeposition. This work offers an attractive strategy for fabricating Co-Ni alloy coating as protective layers to increase the lifetime of components exposed to corrosion and wear condition.

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