Corrosion behavior of Cr–P/nano Al2O3 composite coatings

Abstract

The effect of Al2O3 nano-particles incorporation on corrosion resistance and micro hardness of chromium-phosphorous coatings was investigated. For this purpose, different amounts of alumina nano-particles (i.e. 0–35 g l−1) were dispersed in the plating bath. Dynamic light scattering/Zeta potential analyzer was used to determine the dispersion or agglomeration tendency of nano-particles in the plating bath. Scanning electron microscope (SEM), equipped with an energy dispersive spectroscope (EDS) and optical microscope (OM), was used to study the morphology and the chemical compositions of the coatings. Corrosion behavior of the coatings was studied via electrochemical impedance spectrometry (EIS) and linear polarization tests in a 3.5 wt% NaCl solution at ambient temperature. Micro hardness of the coatings was also studied via a micro hardness tester. According to the results, phosphorous content of the coatings was decreased from 17.5 wt% to 11.5 wt% as the amount of alumina nano-particles increased in the plating bath. Similarly, micro crack density of the coatings was also decreased. Also, composite coatings revealed higher corrosion resistance and micro hardness. Corrosion current density was decreased from 2 μA cm−2 to 0.2 μA cm−2 and hardness of the coatings was increased from 600 HV to 930 HV, as the composition of the coating was converted from pure Cr–P alloy coating to Cr–P/nano Al2O3 composite coating.