Development of Mg-Gd-(Ag, Ca) alloys as biodegradable implant materials (Dissertation)

Mg alloys attract more and more attention as a new generation of biodegradable implant materials. However, they still have some drawbacks such as fast uncontrollable corrosion and a high amount of produced hydrogen bubbles during corrosion process. Moreover, knowledge on the effects of alloying elements and intermetallic phases in physiological environments is necessary to be further understood. Therefore, it is extremely important to develop novel Mg alloys combining proper mechanical properties, controllable homogeneous degradation properties with low degradation rate and good biocompatibility. Mg-RE (rare earth) alloys show a good combination of increased mechanical properties and bio-corrosion resistance [1-6]. Gd, Ag and Ca are used as the main alloying elements in this work. Gd has an acceptable biocompatibility and a high solid solubility in Mg. It was reported that Mg-Ag alloys showed improved ductility, a good biocompatibility and satisfactory antibacterial properties [7]. Addition of Ca contributes to the microstructure refinement of as-cast Mg alloys, and improvement of their strength and plasticity. Ca as the essential elements in human body is excellent biocompatible. In the present work, systematic studies of pure Mg, binary and ternary alloys were designed for development of Mg-Gd-Ag and Mg-Gd-Ca alloy series for biodegradable implant applications. Pure Mg, binary Mg-xGd (x=0.5, 1, 2 wt.%), Mg-xAg (x=1, 2 wt.%), Mg-xCa (x=0.4, 0.8 wt.%) and ternary Mg-2Gd-xAg (x=1, 2 wt.%), Mg-2Gd-xCa (x=0.4, 0.8 wt.%) alloys were prepared by permanent mould casting method. Their microstructure, mechanical properties, corrosion properties have been fully investigated. The phase diagrams of binary Mg-x(Gd, Ag, Ca) and ternary Mg-2Gd-x(Ag, Ca) alloys are calculated using Pandat software. The predicted phase transformations are compared with the experimental results. Solid solution (T4) heat treatment was carried out to optimize the microstructure and properties of these low-level alloys. Effects of Ag/Ca additions ...