Volume 8, Issue 30 (3-2019)
Abstract
The main objective of the present study was to apply a polymer coating made of Polycaprolactone/chitosan (PCL/Ch) /1%wt. Baghdadite to an anodized AZ91 alloy through the immersion method in an attempt to improve these alloy's resistance to corrosion, bioactivity, and biocompatibility. The results of the corrosion test were indicative of an improvement in the corrosion resistance and a 103-fold decrease in the corrosion current density of the anodized AZ91 alloy as a result of applying the polymer-ceramic coating. Moreover, applied the polymer-ceramic coating increased the roughness of AZ91 from 0.329 ± 0.02 to 7.792 ± 0.34 μm. Simulated body fluid (SBF) was used to evaluate the apatite formation ability of the samples. The results showed the formation of an apatite layer on the sample surface which can be considered as a bioactivity criterion.
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Volume 10, Issue 35 (3-2020)
Abstract
Plasma electrolytic oxidation is a novel and promising method for coating the light alloys especially magnesium alloys. Several parameters affect the coating quality and its properties, where in this study; the effects of frequency on properties of coatings produced by PEO on AZ31 Mg alloy were investigated. The coating process was performed in a silicate-based electrolyte containing KF and K2TiF6 using a soft-sparking waveforms with 30 % cathodic pulse width at 1, 2, and 3 kHz. The surface morphology of the coatings was a net-like (scaffold) containing a micro-pores network, micro-cracks, and granules of oxide compounds, in which, no noticeable change on coating morphology occurred with increasing the frequency. Also, the coatings were composed of MgO, MgF2, Mg2SiO4, SiO2 (amorphous), and TiO2 (crystalline and amorphous) phases contributed by the elements from both substrate and electrolyte in the coating process. Based on the cross-sectional images, the thickness of coatings displayed no significant increase with increasing in frequency, but the porosity percentage was increased. Also, the very small pores were presented in the inner layer with increasing frequency. Corrosion behavior of the coatings was evaluated using electrochemical impedance spectroscopy (EIS) in 3.5 wt. % NaCl until 7 days of immersion. The results of the EIS showed that with increasing frequency and porosity, the larger surface of the coating is in contact with the solution, and the presence of porosity in the more compact layer of the coating allowed the access of solution to the substrate, which reduces the barrier performance of the coating.
