Evaluation of the corrosion resistance of AlCoCrFeMnNi high entropy alloy hard coating applied by electro spark deposition

Abstract

Although hard coatings have good resistance to wear and scratching, their corrosion resistance has decreased, failing. Improving the corrosion resistance of the hard coating has lately become a difficult subject. This work produced a newly created AlCoCrFeNiMn alloy with a high entropy using mechanical alloying and spark plasma sintering. Aluminum was added as the sixth elemental component to the chemical composition of the CoCrFrNiMn high entropy alloy to achieve this objective. Subsequently, the AlCoCrFeNiMn layer was deposited via electro-spark deposition on a substrate (ESD). To achieve a uniform layer, parameter optimization was performed, and the effects of frequency (5, 8, and 11 kHz), duty cycle (50, 60, and 70 %), and applied current (15, 25, and 35 A) were studied. Using the Vickers technique, the acquired surface microhardness of coatings was measured. The most significant measurement of hardness was around 1426 HV0.05. Using potentiostat-polarization testing and electrochemical impedance spectroscopy at room temperature, the corrosion of the coatings was evaluated. The AlCoCrFeNiMn HEA coating considerably increased the corrosion resistance of the substrate, according to the results. Corrosion rates for uncoated and coated samples were 1.44 and 0.13, respectively. At the optimal frequency of 11 kHz, the duty cycle of 60 %, and the current of 35 A, the coating exhibited the highest corrosion resistance, which was 10 times greater than the corrosion rate of the substrate. All of the coated samples displayed a passivation behavior, ascribed to the production of chromium oxide and aluminum oxide on the surface of the HEA layers due to their lower free Gibbs energy formation values. In addition, the coating's roughness was assessed, and the correlation between surface roughness and corrosion resistance was determined.