Microstructure, Mechanical And Degradation Properties Of Magnesium-yttruim Based Biomaterials

Magnesium(Mg) alloys have attracted great attention as biomedical materials due to their appropriate mechanical properties and suitable degradation rate in physiological environment. Nevertheless, biomedical magnesium alloys require, and what is most important, biosafety to human body. The yttrium(Y) element has been recently reported as an effective alloying addition to prepare Mg-based biomaterial. Of particular importance is that the mechanical properties and anti-corrosion properties of Mg alloys can be improved by adding Y alloying element. More attractively, the toxic range of Y is wide and its metabolic pathway is clear. Thus, Mg-Y based system is regarded as a potential one to manufacture bio-Mg materials. The effect of backward extrusion and melt extraction technique on microstructue, mechanical and degradation of Mg-Y based biomaterials is investigated.Microstructures, aging behaviour from room temperature to 300 ℃and mechanical properties in different media of backward extruded(BE) Mg–Y based biomaterial have been investigated.The results reveal that BE-Mg–Y based alloy is mainly composed of polygon-shaped grains and fine precipitates. The results of aging response show that BE-Mg–Y based alloy exhibits remarkable age hardening behaviour when the aging temperature is 200 ℃and higher. The high mechanical properties of aged BE-Mg–Y based alloy are mostly associated with fine microstructure, solid solution strengthening and the existence of homogeneous precipitates. The hydrogen embrittlement dependence on the aging time is confirmed in BE-Mg–Y based alloy. Additionally, the strength and elongation of BE-Mg–Y based alloy are significantly influenced by the ion concentration in media.These results offer some implications for understanding the reduced strength of Mg based implants in body environment. It is demonstrated that the temporary high mechanical strength in air of BE-Mg–Y based biomaterials is insufficient to evaluate the in vivo mechanical integrity.Mg-Y-based microwire which offers high strength in combination of low degradation rate has been prepared for the first time by a modified melt extraction technique. A circular Mg-Y-based microwire is achieved with an extraction rate of 40 m/s, which is composed of Mg matrix and an amorphous phase, and exhibits higher basal texture than that of as-cast sample. The outstanding tensile strength accompanying with an acceptable elongation is obtained with an extraction rate of 40 m/s. The improved strength is mainly attributed to high solid solution strengthening, fine grain and the presence of an amorphous phase. In addition, the reduction of secondary phase and homogenous microstructure after melt extraction eliminate both pitting corrosion and micro-galvanic corrosion. A low degradation rate of 0.366 mm/y is attained in a simulated body fluid, which is less than 1/10 of that of as-cast sample. These excellent mechanical properties and low degradation rate provide some prerequisites to develop bio-Mg implants. It reveals that this modified extraction technique is one of effective approaches to prepare microwire, which can be directly used for Mg-based stent self-assembly.