A Study of Anticorrosion Coatings for Surface Modification of Biodegradable Magnesium Alloy

Magnesium alloys material would dissolve easily in body fluid which contains chloride ion, and the corrosion products are necessary to the human body. Due to the suitable mechanical property, biocompatibility and biodegradability, magnesium alloys are promising in the development of bio-absorbable orthopedic implants for interventional therapy and bone tissue engineering. However, a rapid corrosion rate resulted form the intrinsically active response of magnesium alloys to chloride-containing blood plasma and human body fluid remains the problem. Subsequently, a better understanding of the interaction between magnesium alloys and human body environment is the prerequisite to lower the corrosion rate. The surface modification technique could change the surface composition and the degradation rate of magnesium alloys. In this study, Diamond-like carbon films (DLC) are deposited on AZ31 magnesium alloy by combining plasma enhanced unbalance magnetron sputtering physical vapor deposition (PEUMS-PVD) and microwave electron cyclotron resonance plasma enhanced chemical vapor deposition (MW-ECR PECVD) techniques. In these techniques, the SiC interlayer is introduced between metallic substrates and DLC films by using methane (CH₄) and silicon target in order to increase the coating’s adherence. The corrosion behavior of the DLC films in simulated body fluid and biocompatibility have been measured and evaluated synthetically by the surface analysis technique, electrochemical measurement and hemocompatibility experiments.The present study demonstrated that DLC films were successfully formed by PECVD on Mg alloy substrate. Both films are composed of graphite that had a disorderedgraphite-like structure. Silicon component of Si/SiC intermediate layers suppresses the formation of sp² graphitic clusters and increases the sp³ bonding and the hydrogen content in the DLC films. Based on these observations, it might be concludedthat DLC films on the Mg alloy substrate leads to a moderate increase in degradation resistance. As a hard DLC film was formed on the Mg alloy substrate, further study is worthwhile to check biocompatibility of these coatings and improve the quality of the film.