新型生物医用Mg-Dy-Sr-Nd-Zr合金及其压铸态的组织与性能研究

发布时间：2019-06-02 05:20

【摘要】：生物镁合金材料凭借其良好的生物相容性、力学相容性及生物可降解性,受到医学界及材料界的广泛关注,但是降解过程的控制及精密成型等难题限制了其在医疗领域的临床应用。近年来,稀土元素成为生物镁合金材料在合金化方面的研究热点,含有稀土的WE43医用镁合金同时具有良好的力学性能及耐腐蚀性能。为了开发出更能适应人体环境的生物医用镁合金,在WE43合金的基础上,替换其中稀土元素,选择了没有毒性的稀土元素Dy及生物相容性良好的元素Sr作为合金化元素。利用金属模浇铸制备了Mg-xDy-ySr-2.4Nd-0.5Zr(x=2、6、10;y=0.5、1.5、2)合金,通过光学显微镜(O M)、扫描电镜(SEM)、室温拉伸试验、电化学及失重实验分别分析了不同含量的Dy以及Sr元素对生物医用镁合金材料的显微组织、力学性能以及生物降解性能的影响。针对生物镁合金塑性差的问题,再对具有良好力学性能及耐腐蚀性能的Mg-10Dy-0.5Sr-2.4Nd-0.5Zr合金采用压铸成型工艺,并对比分析铸态及压铸态生物医用镁合金的组织与性能之间的内在规律。铸态Mg-xDy-ySr-2.4Nd-0.5Zr合金的晶粒呈树枝状生长,其平均晶粒尺寸随着Dy元素含量的增加发生明显细化。Sr元素对生物镁合金的晶粒尺寸细化效果并不明显,但是过量的Sr元素会增加镁合金偏聚的倾向。铸态合金中第二相由Mg2 Dy、Mg3Dy、Mg17Sr2、Mg12N d相组成并沿着晶界析出。D y元素的增加可以通过固溶强化、细晶强化的作用使镁合金的力学性能得到提高。然而过量的Sr元素导致镁合金晶粒分布不均从而产生应力集中,因此镁合金的力学性能随着Sr含量的增加反而下降。铸态生物医用Mg-10Dy-0.5Sr-2.4Nd-0.5Zr合金具有最佳的力学性能,其抗拉强度、屈服强度及延伸率依次为203MPa、128MPa、7.4%。生物医用Mg-xDy-ySr-2.4Nd-0.5Zr合金的耐腐蚀性能随着Dy元素的增加通过细化晶粒得到增强。Mg17Sr2容易与α-Mg相发生电偶腐蚀,因此镁合金的腐蚀速率随着Sr元素含量的增加呈增大的趋势。铸态Mg-10Dy-0.5Sr-2.4Nd-0.5Zr合金在PBS模拟体液中具有最佳的耐腐蚀性能,降解速率为0.58mm/a。压铸成型没有改变Mg-10Dy-0.5Sr-2.4Nd-0.5Zr合金的相组成,但是沿晶界分布的第二相呈细小网格状分布。压铸态合金的晶粒尺寸明显细化至18μm,晶粒形态由树枝晶向等轴晶转变。晶粒大小不均匀并且合金内部的气孔导致压铸态Mg-10Dy-0.5Sr-2.4N d-0.5Zr合金的强度降低,但是压铸态镁合金的拉伸断口出现大量的韧窝和撕裂棱,并且延伸率增加,说明压铸态Mg-10Dy-0.5Sr-2.4Nd-0.5Zr合金的塑性明显增强,断裂类型属于准解理断裂。因此,压铸成型技术改善了生物医用镁合金的塑性变形能力。压铸态镁合金的腐蚀产物溶解速率大于其修复速率,在镁合金的腐蚀层中没有形成稳定的Mg(OH)2保护膜,极化曲线同样表明压铸态镁合金没有发生钝化行为。因此压铸成型降低了Mg-10Dy-0.5Sr-2.4Nd-0.5Zr合金的耐腐蚀性能。压铸态镁合金的腐蚀类型也发生了改变,由铸态合金的局部点腐蚀转变为均匀腐蚀。
[Abstract]:With its good biocompatibility, mechanical compatibility and biodegradability, the biological magnesium alloy material is widely concerned by the medical community and the material world, but the control and precision molding of the degradation process have limited its clinical application in the medical field. In recent years, rare earth elements have become hot spots in the alloying of magnesium alloy materials, and the WE43 medical magnesium alloy containing rare earth has good mechanical properties and corrosion resistance. In order to develop a biological medical magnesium alloy which is more suitable for human environment, the rare earth element is replaced on the basis of the WE43 alloy, and the rare earth element Dy with no toxicity and the element Sr with good biocompatibility are selected as the alloying elements. Mg-xDy-ySr-2.4 Nd-0.5Zr (x = 2,6,10; y = 0.5, 1.5,2) alloy was prepared by metal mold casting, and the microstructure of the biological medical magnesium alloy material was analyzed by optical microscope (O M), scanning electron microscope (SEM), room temperature tensile test, electrochemical and weight loss experiment. And the effect of the mechanical property and the biodegradability. In order to solve the problem of the plastic difference of the biological magnesium alloy, an Mg-10Dy-0.5Sr-2.4 Nd-0.5Zr alloy with good mechanical properties and corrosion resistance is adopted to adopt a die-casting forming process, and the internal law of the microstructure and the property of the as-cast and die-cast biomedical magnesium alloy is compared and analyzed. The grain size of the as-cast Mg-xDy-ySr-2.4 Nd-0.5Zr alloy is dendritic growth, and the average grain size of the as-cast Mg-xDy-ySr-2.4 Nd-0.5Zr alloy is obviously refined with the increase of the content of the Dy element. The effect of Sr element on the grain size refinement of the biological magnesium alloy is not obvious, but the excessive Sr element will increase the tendency of the magnesium alloy to become more and more. The second phase in the as-cast alloy is composed of Mg2 Dy, Mg3Dy, Mg17Sr2 and Mg12Nd and is precipitated along the grain boundary. The increase of the D y element can improve the mechanical properties of the magnesium alloy by solution strengthening and fine grain strengthening. However, the excessive Sr element results in uneven distribution of the grain distribution of the magnesium alloy, and the stress concentration is generated, so the mechanical property of the magnesium alloy decreases with the increase of the Sr content. As-cast biomedical Mg-10Dy-0.5Sr-2.4 Nd-0.5Zr alloy has the best mechanical property, and its tensile strength, yield strength and elongation are 203 MPa,128 MPa and 7.4%. The corrosion resistance of the biomedical Mg-xDy-ySr-2.4 Nd-0.5Zr alloy can be enhanced by refining the crystal grains with the increase of the Dy element. Mg17Sr2 is susceptible to galvanic corrosion with the Mg-Mg phase, so the corrosion rate of the magnesium alloy increases with the increase of Sr element content. As-cast Mg-10Dy-0.5Sr-2.4 Nd-0.5Zr alloy has the best corrosion resistance in the body fluid of PBS, and the degradation rate is 0.58mm/ a. The phase composition of the Mg-10Dy-0.5Sr-2.4 Nd-0.5Zr alloy is not changed in the die-casting process, but the second phase along the grain boundary is distributed in a fine mesh shape. The grain size of the die-cast alloy is obviously thinned to 18 & mu; m, and the grain morphology is changed from the dendritic to the like. The grain size is not uniform and the air holes in the alloy lead to the decrease of the strength of the die-cast Mg-10Dy-0.5Sr-2.4 Nd-0.5Zr alloy, but the tensile fracture of the die-cast magnesium alloy has a large number of dimple and tear edges, and the elongation is increased, indicating that the plasticity of the die-cast Mg-10Dy-0.5Sr-2.4Nd-0.5Zr alloy is obviously enhanced, The fracture type belongs to the quasi-cleavage fracture. Therefore, the die-casting technology improves the plastic deformation capacity of the biomedical magnesium alloy. The dissolution rate of the corrosion product of the magnesium alloy in the die-casting state is higher than the repair rate, and the stable Mg (OH)2 protective film is not formed in the corrosion layer of the magnesium alloy, and the polarization curve also shows that the magnesium alloy in the die-casting state has no passivation behavior. And the corrosion resistance of the Mg-10Dy-0.5Sr-2.4 Nd-0.5Zr alloy is reduced. The corrosion type of the magnesium alloy in the die-casting state has also changed, and the local point corrosion of the as-cast alloy is changed into uniform corrosion.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R318.08;TG146.22;TG249.2

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