【作者】 王彬；

【导师】 关绍康；

【作者基本信息】 郑州大学 ， 材料加工工程， 2012， 硕士

【摘要】 可降解镁合金血管支架是当前国内外的研究热点,但其耐腐蚀性能和力学性能仍然不能满足血管支架的要求。目前较多报道集中在通过合金化及塑性变形工艺以细化镁合金晶粒从而提高其强韧性,但挤压等变形工艺引入的应力会降低镁合金的耐腐蚀性能。因此,如何利用合金化及加工工艺制备出同时具有优异的耐腐蚀性及高强韧的材料是镁合金应用于血管支架亟待解决的问题。针对于此,本文选择具有良好的力学性能和耐腐蚀性能的低锌系Mg-2Zn-0.2Y合金,仅含有与人体生物相容的元素,微量添加对人体无毒、可提高材料抗凝血性及合金强韧性和耐腐蚀性能的稀土元素Nd,同时采用亚快速凝固工艺(铜模喷铸)以细化镁合金组织,避免变形应力,提高基体固溶度,从而获得与血管支架尺寸相当的具有良好综合性能的Mg-Zn-Y-xNd合金。通过金相显微分析,X射线衍射分析、电化学测试、溶血凝血试验、压缩试验等方法研究了亚快速凝固Mg-Zn-Y-xNd合金的显微组织、体外腐蚀特性及生物相容性和力学性能,为血管支架用镁合金成分与工艺的最佳配合提供有效的基础数据和实践依据,并为下一步制备支架用微管奠定基础。研究结果表明：Mg-Zn-Y-xNd合金(x=0,0.5,1.0,1.5,wt%)经亚快速凝固后显微组织变化明显,主要由花瓣状树枝晶组成,枝晶臂为4-5μm左右；含适量Nd合金二三次枝晶臂变得不明显；合金中大部分的Zn. Nd元素固溶于a-Mg基体中,XRD中仅显示α-Mg的衍射峰,且相对于普通凝固合金的α-Mg衍射峰向右偏移约0.14°；对于普通凝固Mg-Zn-Y-xNd合金(x=0,0.5,1.0,1.5,wt%),随Nd含量增加,晶粒先细后粗,晶粒度为400→90→70→440μm；合金晶界处第二相增多,变得连续,由点、棒状→线状；加入Nd1.5%Nd时枝晶粗大；合金中出现了NdZn及NdZn2相。对于亚快速凝固(Φ3mm)Mg-Zn-Y-xNd合金(x=0,0.5,1.0,1.5,wt%),显微组织中出现花瓣状树枝晶,随Nd含量增加,枝晶臂变得明显,二次枝晶臂间距均在5μm左右；对于亚快速凝固(Φ2mm)Mg-Zn-Y-xNd(x=0,0.5,1.0,1.5,wt)合金,横截面易出现三晶区组织,加入Nd使一次枝晶臂大小均匀,稍多时使枝晶臂变长,二次枝晶臂间距均在4μm左右；亚快速凝固下各合金主要为固溶一定量合金元素的§-Mg相；Mg-Zn-Y-xNd合金(x=0,0.5,1.0,1.5,wt%)经亚快速凝固后,各合金的腐蚀电位、开路电位增大,腐蚀电流密度减小,转移电阻和阻抗模增大,合金的耐腐蚀性能提高,且对于Mg-Zn-Y-1.0Nd合金最为显著；随Nd含量增加,亚快速凝固(Φ3mm与Φ2mm)和普通凝固下Mg-Zn-Y-Nd合金的腐蚀电位、开路电位均增大,腐蚀电流密度先减小后增大,转移电阻和阻抗模先增大后降低,在Nd含量为1.0%时腐蚀电流密度最小,转移电阻和阻抗模最大,即耐腐蚀性能达最优。Nd能够减小镁合金发生腐蚀的倾向,适量加入Nd可降低腐蚀速率,提高耐蚀性；亚快速凝固增强了Nd提高Mg-Zn-Y-Nd合金耐腐蚀性能的作用。在普通凝固与亚快速凝固(Φ3mm)两组冷速下,Mg-Zn-Y-1.0Nd合金耐腐蚀性能优于Mg-Zn-Y-0.5Nd合金的程度不大；在亚快速凝固(Φ2mm)下,Mg-Zn-Y-1.0Nd合金耐腐蚀性能优于Mg-Zn-Y-0.5Nd合金显著(腐蚀电流密度减小了45.1%,转移电阻增大了85.5%)。所有合金中,亚快速凝固((Φ2mm)Mg-Zn-Y-1.0Nd合金耐腐蚀性能最好,优于已经用于制备血管支架的WE43合金；考虑到亚快速凝固(Φ2mm)合金易形成三晶区,以及实际血管支架是对微管形状材料的内外回转面性能有要求,对比研究了亚快速凝固(Φ2mm)Mg-Zn-Y-1.0Nd合金的回转面与截面的腐蚀性能。动电位极化试验、电化学阻抗分析及浸泡试验均表明亚快速凝固圆柱形试棒回转面的耐腐蚀性能优于截面,这非常有利于亚快速凝固Mg-Zn-Y-1.0Nd合金充分发挥其表层细晶区的优异耐腐蚀性能而应用于血管支架。经亚快速凝固,Mg-Zn-Y及Mg-Zn-Y-1.0Nd合金的血液相容性提高；加入1.0%Nd使合金溶血率降低,活化部分凝血活酶时间延长,亚快速凝固下更明显；普通凝固及亚快速凝固Mg-Zn-Y-1.0Nd合金的溶血率及APTT均优于WE43合金和316L不锈钢；亚快速凝固Mg-Zn-Y-1.0Nd合金其浸提液培养的细胞生长形态较好,细胞存活率高,细胞毒性为1级,达到国家对生物材料安全性要求；随Nd含量增加(0→1.0,wt%),亚快速凝固下Mg-Zn-Y-Nd合金显微硬度和压缩强度增大,最大压缩应力时应变变化不大；普通凝固Mg-Zn-Y-Nd合金显微硬度、拉伸强度和压缩强度增大,伸长率先增后减：经亚快速凝固,Mg-Zn-Y-xNd(x=0,0.5,1.0)合金的显微硬度和压缩强度提高,普通凝固各合金在压缩试验中的脆性断裂转变为塑性失效,且对于Mg-Zn-Y-1.0Nd合金的效果最明显。更多还原

【Abstract】 Biodegradable magnesium (Mg) alloys are attracting most attention in the field of vascular stents all over the world; however, their corrosion and mechanical properties of Mg alloys haven’t fully satisfied the corresponding requirements. Most current studies focus on grain refinement of Mg alloys through alloying and plastic deformation, but deformation technologies, like extrusion, will introduce extrusion stress which badly affects the corrosion resistance of Mg alloys. Therefore, to develop new Mg alloys with both excellent corrosion resistance and exceptional mechanical properties for degradable stents, how to optimize alloying and new processing technologies is an urgent and cruicial problem.Based on Mg-Zn-Y alloy with low Zn content and only biocompatible elements, which has good mechanical and corrosion properties, this paper micro alloyed rare earth element Nd wich is nontoxicious to human, can improve the anticoagulant property and has obvious refinement on Mg alloys, and chosen subrapidly solidification (copper mold casting) to refine microstructure, avoid the deformation stress, enhance the solid solutin ability of α-Mg phase, to obtain Mg-Zn-Y-Nd alloys with excellent properties and comparable size with stents. Microstructure, in vitro degradation and biocompatibility and mechanical properties of subrapidly solidified Mg-Zn-Y-xNd alloys were studied through Optical microscopy, X-ray diffraction, electronchemical tests, hemolysis tests, and so on, hoping to provide useful practical reference to the research on the best match of alloying and processing techniques, and basis for next step of preparation of small tubes for stents.The results showed that:After subrapid solidification, microstructures of Mg-Zn-Y-xNd (x=0,0.5,1.0,1.5, wt%) alloys changed obviousely:most were rosette-like dendrites, the secondary dendrite arm space (SDAS) was around4-5μm, secondary dendrites of alloys with certain Nd content turned not obvious, and most of Zn and Nd elements were solid soluted into the a-Mg substrate, which led to that there are only peaks of α-Mg phase in XRD, and they showed offset to the right compared to those of cast alloysFor the as-cast Mg-Zn-Y-xNd (x=0,0.5,1.0,1.5, wt%) alloys, with the increase of Nd content, grains became firstly smaller and then bigger,400→90→70→200μm; the amount of second phase along grain boundries increased, and their morphologies were rodlike→lineship; excessive amount of Nd increased the tendency of dendrite formation, and there were NdZn and NdZn2phases. For the subrapidly solidified (Φ3mm) Mg-Zn-Y-xNd (x=0,0.5,1.0,1.5, wt%) alloys, rosette-like dendrites appeared. With the increase of Nd content, dendrites became more obvious, but the SDAS remained nearly the same, about5p.m. For subrapidly solidified (Φ2mm) Mg-Zn-Y-xNd (x=0,0.5,1.0,1.5, wt%) alloys, typical microstructure of three-crystal zone easily appeared in the cross section. Nd addition can homogenize the size of secondary dendrite arms, excessive addition would promote dendrites to become longer, but the SDAS was about4μm for all Φ2mm alloys. The main phase for subrapidly solidified alloys (Φ3mm and Φ2mm) was α-Mg solid solution.For Mg-Zn-Y-xNd (x=0,0.5,1.0,1.5, wt%) alloys, after subrapid solidification, corrosion potential and open circuit potential increased, corrosion current density decreased, and charge transfer resistance increased, indicating that the corrosion resistance of alloys were improved, and this improvement was most effective for Mg-Zn-Y-1.ONd alloy.With the increase of Nd content, for as-cast and subrapidly solidified (Φ3mm and Φ2mm) alloys, the corrosion potential and open circuit potential increased, corrosion current density decreased firstly and then increased, and charge transfer resistance increased firstly and then decreased. The corrosion resistance got best when the amount of Nd addition is1.0%. Nd can decrease the tendency of corrosion reaction; a moderate amount of Nd can reduce the corrosion rate and improve the corrosion resistance.The effects of Nd in improving corrosion resistance of Mg-Zn-Y-Nd alloys were strengthened by subrapid solidification. In as-cast and subrapid solidification (Φ3mm) groups, the improvement in corrosion resistance of Mg-Zn-Y-1.0Nd alloy was not obvious; while in subrapid solidification (Φ2mm) group, that improvement was great. Among the alloys studied, subrapidly solidified (Φ2mm) Mg-Zn-Y-1.0Nd alloy possessed best corrosion resistance, which was better than WE43alloy that has been used as vascular stent material.Considering the microstructural characteriastics of subrapidly solidified (Φ2mm) alloys, and that it is the properties of cylindrical surface of small tube material that matter most for vascular stents, the corrosion properties of cylindrical surface (CS) and sectional surface (SS) of subrapidly solidified (Φ2mm) Mg-Zn-Y-1.ONd alloy were studied. Potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) and immersion tests indicated that CS had better conrrosion resistance than SS, which is beneficial for subrapidly solidified Mg alloys to maximize its strengths and avoid its disadvantages to be used as stents.After subrapid solidification, hemocompatibility of Mg-Zn-Y and Mg-Zn-Y-l.ONd alloys were improved; an addition of1.0%Nd can decrease the hemolysis and make APTT longer, and those effects were more obvious in subrapidly solidified alloys; hemolysis and APTT of as-cast and subrapidly solidified Mg-Zn-Y-1.ONd alloys were better than those of WE43and316L stainless steel; the cells cultured in extracts of subrapidly solidified Mg-Zn-Y-l.ONd alloys showed good morphology and had high cell viability, the cytotoxicity was1class, indicating the alloy has met national requirement for biomaterials.With the increase of Nd content (from0to1.0%), microhardness and compressive strength of subrapidly solidified Mg-Zn-Y-Nd alloys increased, but strain at compressive strength had little difference; microhardness, tensile strength and compressive strength of as-cast alloys increase, elongation increases firstly and then decreases. After subrapid solidification, microhardness and compressive strength of Mg-Zn-Y-xNd (x=0,0.5,1.0%) were improved, and the brittle fracture in as-cast alloys turned into plastic failure for subrapidly solidified alloys. These effects were more obvious for Mg-Zn-Y-1.ONd alloy.更多还原