Microstructures and corrosion behavior of biodegradable Mg–Ca–xBi AND Mg–Ca–Zn–xBi alloys for biomedical implant application

Abstract

Low density, biodegradable and non-toxicity magnesium (Mg) has received great attention as biodegradable medical implants as it does not require second surgical procedure to remove the implant. However, poor corrosion resistance, rapid degradation and hydrogen gas evolution in human body fluid have limited its clinical application. This research is aimed to investigate the effect of bismuth (Bi) on the microstructures and corrosion behavior of Mg based alloy. The first stage of the research was focused on the effect of Bi on the binary Mg-Ca alloy by the addition of Bi from 0.5 to 12wt.%. The same process was repeated in the second stage by replacing binary Mg–Ca alloy with ternary Mg–Ca–Zn alloy. Microstructural analysis was conducted by optical microscopy, X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The corrosion resistance was investigated by using in vitro immersion tests and electrochemical test in Kokubo simulated body fluid (SBF). The results show that the grain size decreased with addition of Bi contents in both Mg-Ca-xBi and Mg-Ca-Zn-xBi alloys. SEM micrograph shows that the amount of intermetallic phases increased with increasing of Bi content in both ternary and quaternary alloys. The addition of 0.5 wt.% Bi content was found to enhance the corrosion resistance of both Mg based alloys and produced the lowest dissolution rate. Further addition of Bi content up to 12wt.% have deteriorate the corrosion resistance. These results show that the Bi element would enhance the corrosion behavior of Mg based alloys when it is solutes inside the a-Mg matrix. The precipitation of the intermetallic phases was detrimental to the corrosion resistance. The overall results show that Mg–Ca–0.5Bi and Mg–Ca–Zn–0.5Bi alloys presented highest corrosion resistance hence it can be good candidates for biomedical implant applications.