A Comparison of Corrosion Behavior in Saline Environment: Rare Earth Metals (Y, Nd, Gd, Dy) for Alloying of Biodegradable Magnesium Alloys

Rare earth (RE) metals are widely used as the alloying elements in biodegradable magnesium alloys as medical implants. However, corrosion behavior of pure RE metals not only in physiological media but also in chlorinated saline environment is not well understood. In the present work, the RE metals Y, Nd, Gd and Dy are selected to investigate their corrosion behavior in 0.1 mol/L NaCl solution with immersion and electrochemistry techniques. As indicated, corrosion of the currently investigated RE metals is promoted in the order of Dy, Y, Gd and Nd. In terms of electrochemical response, such a sequence correlates with the increased impedance and the decreased corrosion rate (CR). These RE metals manifest weak ability for passivation in the native surface. Then, reaction with aqueous solution easily happens through the anodic dissolution and cathodic hydrogen evolution. The corrosion products, RE(OH)3, adhered on the surface of RE metals, do not have an appreciable power to resist the reaction proceeding with corrosive chloride ions. In contrast to pure Mg, the RE metals, including Y, Nd, Gd and Dy, exhibit significantly fragile corrosion resistance in saline media. Therefore, with the current findings, it is impossible to reveal a well-defined correlation of corrosion resistance between RE-containing Mg alloy and RE metal itself.