The Effect of Strontium Content on the Corrosion Behavior of New Biodegradable Mg-1Ca-1Y Composite for Implant Application

Abstract

In this study, new biodegradable magnesium composites Mg-1Ca-1Y-xSr (x = 0.5, 1.0, 1.5, and 2.0) were designed and produced by mechanical alloying to improve the corrosion properties. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were employed to characterize the resulting biodegradable magnesium composites. Besides, the corrosion process was monitored with the help of electrochemical corrosion testing methods, such as open circuit potential (OCP), anodic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that the microstructure of the composites consisted of different phases, with their amounts increasing when adding Sr. Moreover, the phase analysis revealed the formation of intermetallic phases Mg2Ca, Mg17Sr2, and Mg24Y5 in the composites. The immersion of composites in 0.9 wt.% NaCl solution exhibited cathodic potential after 2 h. Enhanced corrosion potential was obtained for a 2.0 wt.% Sr composite. In contrast, composite A with the lowest Sr content exhibited higher cathodic corrosion potential. Analysis of the anodic curves revealed passivation behavior for all composites after immersion into the solution. In addition, pitting was observed on the sample's surface, and the potential for pitting increased for the Mg-1Ca-1Y composite. On the other hand, a semi-circle capacitive loop was noted for all composites, and polarization resistance of the film was better for Mg-1Ca-1Y-2Sr than other samples. That is probably due to the involvement of Sr in the protective oxide layer and the decrease of the galvanic effect in the microstructure. In general, the addition of Sr was favorable for the new biodegradable Mg-1Ca-1Y composite, which may be considered a promising candidate for biodegradable magnesium implants.