【作者】 徐吉林；

【导师】 赵连城； 王福平；

【作者基本信息】 哈尔滨工业大学 ， 材料物理与化学， 2009， 博士

【摘要】 为提高医用NiTi合金的耐腐蚀、耐磨性能和抑制Ni离子释放,增强合金的使用安全性和生物相容性,本文采用双向脉冲微弧氧化电源在医用NiTi合金表面制备了低Ni含量的氧化铝陶瓷膜层。采用SEM、XRD、EDS、XPS等手段系统研究了陶瓷膜层的显微组织结构,并对微弧氧化陶瓷膜层的形成机制进行探讨;采用拉伸试验、球-盘摩擦磨损试验、电化学测试技术、体外测试等研究了膜层的结合强度、耐磨性能、耐腐蚀性能和体外生物学性能。在NaAlO₂和NaAlO₂-NaH₂PO₂电解液体系中制备的微弧氧化陶瓷膜主要由γ-Al₂O₃组成,其衍射峰强度随着电解液浓度的增加、处理电压的提高和处理时间的延长而增强。在NaAlO₂电解液体系中制备的陶瓷膜层表面Ni含量只有0.7³at.%,NaAlO₂浓度对膜层表面形貌和粗糙度影响较大,结合强度随NaAlO₂浓度的增加而增加,最大为28MPa。在NaAlO₂-NaH₂PO₂体系中制备的陶瓷膜层表面呈现出典型的微弧氧化多孔形貌,Ni含量为3⁷at.%,且微孔数量和孔径及表面粗糙度随着处理时间、NaH₂PO₂浓度和正负向处理电压的变化呈规律性变化;在0.15mol/L NaAlO₂、0.01mol/L NaH₂PO₂的电解液中,正向电压为400V,处理2⁹0min所得膜层结合强度均大于60MPa,过大的NaH₂PO₂浓度、过高的正向电压和加载负向电压均使膜层结合强度降低。NiTi合金微弧氧化初期通过电解液中的铝酸根离子在NiTi阳极试样表面沉积形成Al₂O₃绝缘膜,为后续的电击穿、等离子体放电创造条件。分析表明陶瓷膜层可分为三层,分别为过渡层、致密内层、多孔外层。过渡层主要由非晶的Ni₂O₃、TiO₂、磷酸盐和Al₂O₃组成,内层是Al₂O₃和少量的Ni₂O₃、TiO₂和磷酸盐,外层是Al₂O₃和极少量的Ni₂O₃、TiO₂。这种结构为膜层提供了优良的结合强度、耐腐蚀性能及耐磨性能。微弧氧化膜层显著地提高了NiTi合金的耐磨性能。NiTi合金与GCr15对磨的摩擦系数为0.75⁰.85,磨损率为3.5μg/Nm,磨损机制主要为磨粒磨损;微弧氧化陶瓷膜层的摩擦系数因制备工艺的不同而在0.6⁰.9之间变化,磨损机制主要为粘着磨损。在正向电压为400V,处理时间为90min条件下所得的膜层,磨损率只有0.4μg/Nm,与基体相比磨损率下降9倍。微弧氧化陶瓷膜层还显著提高了NiTi合金的耐腐蚀性能,有效地抑制了Ni离子的释放。在正向电压为400V,处理时间为90min条件下制备的膜层,与基体相比,其腐蚀性能可提高2个数量级,而Ni离子释放量可降低1个数量级。微弧氧化处理后的NiTi合金具有生物活性,在SBF溶液中浸泡后可诱导出缺钙的类骨磷灰石。通过溶血率、动态凝血时间和血小板黏附结果发现,微弧氧化处理后的NiTi合金血液相容性得到较大改善。体外成骨细胞培养试验发现经微弧氧化处理的NiTi合金表面成骨细胞铺展、繁殖能力增强,表明表面粗糙多孔的氧化陶瓷膜层有效地提高了NiTi合金的生物相容性。更多还原

【Abstract】 The low Ni content Al₂O₃ ceramic coatings on biomedical NiTi alloy were prepared by micro-arc oxidation （MAO） pulsed bipolar power supply in order to improve the corrosion and wear resistance, suppress the release of Ni ions and enhance the use security and biocompatibility of biomedical NiTi alloy. Microstructure of the coatings was systematically observed by SEM, XRD, EDS and XPS, and the formation mechanism of the Al₂O₃ coatings was also analyzed. The bonding strength, corrosion resistance, wear resistance, in vitro biological performance of the coatings were studied by pull-off test, ball-disk friction and wear test, electrochemical test and in intro test, respectively.In the electrolytes of NaAlO₂ and NaAlO₂-NaH₂PO₂, the coatings are both composed of onlyγ-Al₂O₃ crystal phase, and its crystallinity is increased with the increase of the electrolyte concentrations, treatment voltages and treatment times. In the electrolytes of NaAlO₂, the Ni content of the ceramic coatings is about 0.7³ at.%. The surface morphologies and surface roughness of the coatings are greatly influenced by NaAlO₂ concentrations, and the bonding strength of the coatings is enhanced with the increase of the NaAlO₂ concentrations. The maximal value is 28 MPa. In the electrolyte of NaAlO₂-NaH₂PO₂, the surface of the coatings show the typical micro-arc oxidation porous structure, and Ni content is about 3⁷ at.%. The number and size of micro-pores on the surface and the surface roughness of the coatings are varied with the treatment times, NaH₂PO₂ concentrations and treatment voltages. When the electrolyte is 0.15 mol/L NaAlO₂-0.01 mol/L NaH₂PO₂, anodic voltage is 400 V, and treatment times are 2⁹0 min, the bonding strength of the coatings can exceed 60 MPa. More NaH₂PO₂, higher anodic voltages and cathodic voltages addition have negative relation with the bonding strength of the coatings.At the initial stage of MAO process, the aluminate ions in the electrolyte are deposited on the surface of anodic NiTi sample, which promotes the formation of Al₂O₃ insulation film and creates the condition for the subsequent electrical breakdown and plasma discharge. According to combined analysis, the ceramic coatings prepared in NaAlO₂-NaH₂PO₂ electrolyte can be divided into three layers: transition layer, dense inner layer and porous outer layer. The transition layer contains amorphous Ni₂O₃, TiO₂, Al₂O₃ and phosphate. The dense inner layer is mainly composed of Al₂O₃ and a little Ni₂O₃, TiO₂ and phosphate. The porous outer layer also mainly contains Al₂O₃ and a less Ni₂O₃ and TiO₂. The three layers structure is beneficial to provide excellent bonding strength, corrosion and wear resistance for the ceramic coatings on NiTi alloy.Micro-arc oxidation coatings obviously improve the wear resistance of NiTi alloy. The friction coefficient and the wear rate of NiTi alloy against GCr15 steel ball is 0.75⁰.85 and 3.5μg/Nm, respectively, and the wear mechanism is mainly abrasive wear. The friction coefficient of MAO coatings against GCr15 steel ball varies from 0.7 to 0.9 with the different coating preparation process. The friction coefficient of the coatings is more stable than that of NiTi alloy, and the wear mechanism of the coatings is adhesion wear. When the treatment voltage is 400 V and the treatment is 90 min, the wear rate of this coating is 0.4μg/Nm, which indicates that the wear resistance of the coating is 9 times higher than that of uncoated NiTi alloy. Micro-arc oxidation coatings significantly improve the corrosion resistance of NiTi alloy and suppress the release of Ni ions. When the treatment voltage is 400 V and the treatment is 90 min, the corrosion resistance of this coating is about two orders of magnitude higher than that of uncoated NiTi alloy, and the account of Ni ions release is one order of magnitude lower than that of uncoated NiTi alloy.After micro-arc oxidation treatment, the coated NiTi alloy can induce calcium deficiency HA, which indicates that the coated NiTi alloy presents bioactivity. According the results of hemolysis ratio, kinetic clotting time and platelet adherence, it can be concluded that the hemocompatibility of NiTi alloy can be markedly improved after MAO treatment. The in vitro osteoblast culture tests indicate that the coated NiTi alloy has a better cell propagation ability compared to uncoated NiTi alloy, which illustrates that the rough and porous Al₂O₃ coatings can effectively improve the biocompatibility of NiTi alloy.更多还原