Effect of carbon nanotube incorporation on the evolution of morphology, phase and compositional homogeneity, surface oxide chemistry and corrosion behaviour of electrodeposited FeCuMnNiCo-carbon nanotube composite coatings

Abstract

The effect of addition of various concentration of Multi-walled Carbon Nanotubes (0.05, 0.1, 2.5, 5.0, 15.0, 25.0 mg/L) on the corrosion resistance of FeCuMnNiCo high-entropy alloy composite coatings synthesized by electrodeposition method was investigated. The idea behind the reinforcement of CNTs into High Entropy Alloy (HEA) coatings was to utilise the chemical inertness and hydrophobic nature of CNTs which could enhance corrosion resistance behaviour. The experimental results reveal that concentration of CNT had a major effect on microstructure, composition and roughness ultimately influencing electrochemical behaviour of coatings. Owing to the uniform dispersion, till the optimum concentration, CNT played a vital role in homogenizing the composition, making the composite coating surface more smooth, fine-grained, compact with enhanced hydrophobicity (contact angle from 81.250 to 144.70) .Beyond this threshold, non-uniformly dispersed, agglomerated CNTs led to formation of surface defects thus adversely affecting corrosion resistance by promoting galvanic coupling. It was noticed that the nature of passive oxide layer formed on the coating surface had a direct corelation with the corrosion behaviour. As compared to FeCuMnNiCo, the one with 12.50 mg/L CNT had more protective oxides formed in form of stable Feox+2,Ni+2 and Co+3 oxides which led to an increase in protection efficiency by 87.14%.