Magnesium-zinc-calcium alloys have unique advantages of being used as biomedical bone implants since their mechanical properties and biocompatibility are similar to human tissues. However, insufficient strength and poor corrosion resistance have been the major problems to stunt the application. In this paper, the changes of microstructure, mechanical properties and corrosion resistance of ternary Mg-3Zn-0.2Ca (wt.%) with different contents of Mn (0.3, 0.5, 0.7, 0.9, wt.%) are studied. With the increase of Mn content, the grain size of as-cast alloy first decreases and then increases, this indicates that the amount of Mn affects the degree of subcooling of the alloy. At the 320 • C/24 h homogenizing treatment, the large and uneven dendrites are transformed into uniform equiaxed grains, the mechanical properties of alloys with different Mn contents are different on the basis of Mg-3Zn-0.2Ca (wt.%) alloy. The five alloys were extruded into bar with a diameter of 8 mm through hot-extrusion process. Quaternary Mg-3Zn-0.2Ca-XMn (X = 0.3, 0.5, 0.7, 0.9) (wt.%) alloys are investigated and the results show that 0.5 wt.% Mn alloy has the best yield tensile strength (YS) (302 MPa) and good ultimate tensile strength (UTS) (327 MPa). The reason is that the different contents of Mn restrain the dynamic recrystallization in extrusion process, which remarkedly reduced the grain size. Moreover, each alloy is investigated by electrochemical measurements at 37 • C in a simulated body fluid (SBF). The electrochemical results show that the corrosion potential of Mn-contained alloys are increased compared to ternary Mg-3Zn-0.2Ca (wt.%) alloy, and 0.5 wt.% Mn-contained alloy performs the best result.
In this study, a mental matrix composite (MMC) made of Mg-3Zn-0.8Zr alloy as a matrix and β-TCP particles as reinforcements were prepared for investigating the effect of β-TCP spherical particles sized in 100 nm on the microstructure of that alloy. The grains of as-cast or as-extruded Mg alloys systematically decreased from about 80 μm to about 30 μm with the choice of β-TCP contents. X-ray diffraction (XRD) analysis and optical microscopy (OM) observations show that the Mg-3Zn-0.8Zr-β-TCP (1.0 or 1.5, in wt %) composites were composed of various phases in addition to Mg and MgZn2 comparied with Mg-Zn-Zr alloy. New diffraction peaks appearing in the MMC, which suggests that a potential interaction occurred between β-TCP and the matrix. Transmission electron microscopy (TEM) images reveal that secondary phases, which wraps upon the surface of β-TCP, are uniformly distributed in the grains of Mg-Zn-Zr alloy. Energy spectrum analysis shows that the component of dark-colored parts is equivalent to β-TCP, but the component of light-colored parts is Mg-Zn-Ca, which demonstrates that there is a real interaction occurred between the matrix and β-TCP.
A stable n-HA non-aqueous sol was prepared. During the reaction, the gelatin coated the surface of n-HA rod and chemically bonded with the n-HA. PA66 was dissolved in formic acid and then added to n-HA sol with constant stirring for 3 hours at room temperature, a homogenous composite of 40wt.% n-HA and 60wt.% PA66 was successfully synthesized. It was found that no new phases appeared during formulating the n-HA sol and PA66 solution, but the crystallinity of PA66 was lower. The amide groups in the gelatin are same as PA66, the gelatin coated n-HA sol and PA66 solution have very good compatibility. The developed n-HA/PA66 composites were then soaked in a simulated body fluid (SBF) for 1, 2, 3, and 4 weeks, respectively. It was found that the composites immersed for 2 weeks effectively induced a new bone-like apatite layer with lower crystallinity. The n-HA/PA66 composites have much better bioactivity than PA66.
The present investigation was carried out to optimize the hydrogen fluoride (HF) aqueous solution treatment for an Mg-2.5Zn-0.5Zr alloy, in order to improve the corrosion resistance of the material for orthopaedic applications. An MgF2 coating was formed on the surface of Mg-2.5Zn-0.5Zr alloy treated with HF solution. The effect of the HF concentration and processing time on the morphology and electrochemical performance of the MgF2 coating was systematically studied. The results showed that the MgF2 coating became thick gradually with the increase of the concentration of HF solution. However, the pinhole on the surface treated with 40% HF increased significantly. The coating thickness immersed in the same concentration of HF solution increased with immersion time, and cracks formed in the surface after four hours of immersion, resulting in a decrease in the corrosion potential. When the alloy was immersed in the HF solution with a concentration 20% at 37°C for 2h, a uniform and dense fluoride coating was formed, with a thickness of MgF2 layer of about 0.5μm. The corrosion potential of the coated Mg alloy in simulated body fluid (SBF) was 0.28V higher than the uncoated one. In addition, the fluoride-coated showed a good biocompatibility.
Due to the special topography in length and diameter, magnesium oxide (MgO) whisker has good mechanical properties to improve the mechanical and biological properties of biodegradable polymer materials, while the morphology of MgO whisker is significantly related to the morphology of its precursor whisker. In this work the precursor whisker is prepared through the mild solution approach and the effects of three producing factors on the growth of precursor whisker are systematically investigated by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). It reveals that the morphology and composition of MgO predominantly dependent on precursor is prominently influenced by the preparing parameters, especially in solution concentration, aging time and aging temperature. The suitable preparing conditions in present experiment are with 0.6mol/L solution concentration, under 10h aging time and at room temperature, through which the radial dimension of whisker reaches to the nanolevel and the optimal aspect ratio is 80:1.
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