【作者】 刘珣；

【导师】 储成林；

【作者基本信息】 东南大学 ， 材料科学与工程， 2015， 硕士

【摘要】 镁合金是一种应用前景广阔的可降解生物医用材料,通过表面处理可以弥补其在生理环境中腐蚀过快的缺点。本文采用微弧氧化技术对AZ31B镁合金丝材进行表面改性处理,研究了氧化时间和电流密度等微弧氧化工艺参数对镁合金丝性能和微观组织的影响,在此基础上,系统研究了微弧氧化时间、磷酸缓冲液中氯离子浓度以及PLLA封孔处理对镁丝降解性能的影响规律,研究表明：镁合金丝表面微弧氧化膜的组成相以MgO为主,延长氧化时间,陶瓷膜表面裂纹增多,膜层孔隙率先增大后减小,氧化时间为30min (10-30min)时孔隙率最大,而氧化时间对膜层表面孔隙大小没有明显影响；增大电流密度,微弧氧化膜生长速率呈线性上升,表面裂纹增多,孔隙率和平均孔径均先增大再减小,电流密度为8A/dm2(6-108A/dm~2)时两者达到最大值,分别为6.4%和2.59μm。延长氧化时间或增大电流密度都会增加膜层厚度,降低抗拉强度。丝材直径对镁合金微弧氧化陶瓷膜的微观组织影响不大,但膜层孔隙率和平均孔径随丝径增大而减小,丝材强度损失率随之降低。微弧氧化处理会导致小丝径的镁合金丝平均晶粒尺寸略有增大。微弧氧化处理能显著提高镁丝在含血液浓度氯离子的磷酸缓冲液中的耐腐蚀性。短时间浸泡(低于10天),微弧氧化时间的影响不大；浸泡10天后,10min氧化处理的镁丝剩余质量百分数最大。浸泡10天,光丝表面腐蚀严重,而10min氧化处理镁丝表面陶瓷层保持完整。浸泡4天后,10min氧化镁丝的剩余抗拉强度最大,光丝的强度损失率最大。不同浓度氯离子的磷酸缓冲液浸泡实验发现,浸泡相同时间,磷酸缓冲液中氯离子含量越大,镁丝裂纹越多,抗拉强度损失率增大。PLLA涂覆处理后,微弧氧化时间对镁丝浸泡过程中的质量和直径损失率影响小。浸泡33天时,20min和30min氧化并经PLLA涂覆处理的两种镁合金丝表层均保持完整,后者剩余抗拉强度最大。更多还原

【Abstract】 Magnesium alloys are considered as the promising biodegradable materials for biomedical applications and surface modifications are commonly applied to slow down the degradation rate of magnesium alloys in the physiological environment. In this work, micro-arc oxidation (MAO) was used for surface treatment of AZ31B wires. The effect of MAO parameters including MAO time and current densities on the properties and microstructure of the wires was investigated. Moreover, the degradation behaviors of the wires with different MAO time, in different phosphate buffers with various concentration of chloride ion were studied. Furthermore, poly-L-lactic acid (PLLA) was applied to seal the surface pores ofMAO coating and its effect was reported.The results show that the main phase of the MAO coating is MgO and the mean grain size of the wires with small diameter has a little increase after MAO treatment. With the increasing of MAO time, the porosity of the coating increases firstly and then decreases, meanwhile, more cracks are observed at the longer MAO time. The porosity of the coating gets the largest value at MAO time of 30 min, and however, the average pore size has no apparent change with the changing of MAO time. Similarly, with the increasing of the current density (CD), the coating grows with a constant rate and more cracks would appear in the coating, and correspondingly, the tensile strength of the wire decreases. Meanwhile, the values of surface porosity and average pore size of the coating firstly increase and then decreases and at CD of 8 A/dm~2, they have the largest values, which are respectively 6.4% and 2.59μm. While the diameter of the wire increases, the surface porosity and average pore size of the coating has an inverse decrease and the loss of the strength caused by MAO decreases, however, the morphology ofthe coating has no obvious change.The degradation behavior of the wires in the phosphate buffer with the same chloride ion concentrations in the case of flood improves significantly after MAO treatment. During short time immersion (less than 10 days), the MAO time has little effect on the degradation behavior. After 10 days immersion, the remaining mass percentage of 10 min MAO-treated wire kept the highest. For the un-MAO wire, it corroded seriously after 10 days immersion while coating of 10 min MAO-treated wire kept integrated. The loss ratio of the strength of un-MAO wire and remained tensile strength of the wire with 10 min MAO treatment both kept the highest after 4 days immersion. The results of the immersion tests in the phosphate buffer with different chloride ion concentration denote that in the predetermined immersion time, the number of the corrosion cracks and the loss of strength increase with the increasing of chloride ion concentration.With the incorporation of PLLA coating, the effect of MAO time on the loss ratio of mass and diameter of the wire is improved. After 33 days immersion, the 20 min and 30 min MAO-treated wire kept integrated after sealing with PLLA, and the latter one has the largest strength afler immersion.更多还原