The role of bismuth on the microstructure and corrosion behavior of ternary Mg-1.2Ca-xBi alloys for biomedical applications

Abstract

In this study the influence of various Bi additions on the microstructure and corrosion behavior of the Mg-1.2Ca-xBi alloys (x = 0.5, 1.5, 3, 5, 12 wt.%) were evaluated by using optical and scanning electron microscopy, immersion and electrochemical tests. Microstructural observations showed that the refinement efficiency became more pronounced with increased Bi amount. Microstructural results of Mg-1.2Ca-xBi (x = 0.5, 1.5, and 3) indicated that the formation of three distinct phases - namely a-Mg, Mg2Ca and Mg3Bi2. However, further addition of Bi to 5 and 12 wt.% leads to evolution of a-Mg, Mg3Bi2, and Mg2Bi2Ca phases. The addition of Bi up to 0.5 wt.% enhanced corrosion resistance while further addition from 1.5 to 12 wt.% accelerated the degradation rate because of the emergence of more galvanic coupling between the a-Mg phases and secondary phases. The analyses showed that the Mg-1.2Ca-0.5Bi alloy gives the best corrosion resistance behavior, which makes it ideal for biodegradable medical applications.