【作者】 张蕊；

【导师】 艾兴； 万熠； 刘战强；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2016， 博士

【摘要】 医用钛合金因具有良好的力学、物理、化学性能及出色的生物相容性,成为了人造关节,牙植入体及骨创伤产品等硬组织替代物及修复物的首选材料。钛及钛合金植入体在植入之前需要进行表面改性,以提高其耐腐蚀性及生物活性。目前国内外钛合金植入体的表面改性方法均是在机械加工成形之后,其缺点是工艺链长、工艺设备复杂、效率低、成本高。鉴于此,本研究提出了一种切削加工成形与表面改性于一体的钛合金植入体制备新方法；利用切削加工产生的切削热进行表面氧化改性,提高其耐腐蚀性；利用切削加工形成的特定表面形貌提高其生物活性。从可持续发展的角度开发出一种针对钛合金植入体的新型绿色切削加工制备方法,对缩短工艺链、提高效率、降低成本、保护环境、提高钛合金植入体制造技术水平和产品竞争力有重要作用。主要研究工作如下：首先,基于氧化热力学研究钛合金氧化膜产生的机理,确定形成致密二氧化钛膜的条件。基于物理化学理论,分析钛合金氧化过程中钛离子和氧离子的运动规律,揭示钛合金氧化速度的主要控制因素。研究结果表明：形成致密二氧化钛氧化膜的最佳温度范围为600-900℃,此温度范围内钛合金氧化速度的主要控制因素为氧离子通过氧化膜的扩散速度。其次,基于菲克第一定律及阿列纽斯公式建立钛合金氧化动力学模型,研究影响氧化速度的主要因素。采用MATLAB对钛合金氧化动力学模型进行计算,分析各因素对氧化速度的影响规律。研究结果表明：影响钛合金氧化速度的主要因素为氧化温度、富氧浓度及富氧压力、晶粒细化程度及氧化膜厚度；提高氧化温度、富氧浓度及富氧压力、晶粒细化程度可加速钛合金的氧化,但氧化膜厚度的增加会降低钛合金氧化速度。然后,搭建富氧气氛下切削加工工艺试验平台,采用Deform 3D有限元仿真软件对切削参数进行优化,将切削温度控制在最佳氧化温度范围。进行不同切削参数及不同富氧气氛下切削加工试验,对钛合金加工表面氧化膜成分和厚度,表面形貌及表层晶粒进行表征,分析切削温度,富氧浓度和晶粒细化程度等因素对氧化速度的影响规律。将试验结果与理论结果对比,富氧气氛下切削加工能够显著提高钛合金加工表面氧化膜的厚度及致密性,验证了氧化动力学模型的正确性。最后,对富氧气氛下切削加工表面进行耐腐蚀性及生物活性评价。通过模拟体液浸泡试验及电化学腐蚀试验,研究富氧气氛下切削钛合金表面的腐蚀机理和主要影响因素。通过体外细胞培养,观测细胞的黏附、铺展、增殖、分化及矿化等细胞行为,研究加工表面的生物活性,分析加工表面对细胞行为的调控机理。研究结果表明：富氧气氛下切削加工生成的氧化膜能够显著提高钛合金的耐腐蚀性,而且表面形成的微/纳复合结构面形貌有利于蛋白质的吸附,对细胞的黏附,铺展,增殖等细胞行为有较好的调控作用,显著提高了钛合金的生物活性。更多还原

【Abstract】 Medical titanium alloy is the optimal choice for use in prosthetics and substitution of hard tissues such as bone. It is used in joint prostheses, dental implants and bone trauma products for its excellent mechanical strength and corrosion resistance. Titanium alloy implants need certain surface modifications prior to implantation in order to improve their corrosion resistance and bioactivity. Currently, both in China and abroad, preparation of titanium alloy implants is carried out after mechanical processing shaping, where the process chain is long, the equipment processing is complicated, and the efficiency is low while the cost is high. For these reasons, this study proposes a new technique for the preparation of titanium alloy implants, i.e., conducting surface modification while carrying out dry cutting and shaping of implants, where the heat produced during cutting is utilized for oxidative modification to improve corrosion resistance, and certain surface topography is obtained by machining to improve bioactivity. This technique plays a vital role in shortening the process chain, improving efficiency, reducing cost, protecting the environment, enhancing the preparation technology of titanium alloy implants, and ensuring the health of users of such implants. This is a prototypical, "green" machining technique for the preparation of titanium alloy implants with the additional benefit of sustainable development. The main research work is as follows:First, the formation mechanism of titanium alloy oxide films is studied and the formation condition of compact titanium dioxide films is determined according to oxidation thermodynamics. The movement of titanium ions and oxygen ions during the oxidation process of titanium alloy is analyzed to reveal the main controlling factors of the oxidation rate of titanium alloy on the basis of theories of physical chemistry. The study results show that the ideal temperature range for the formation of compact oxide films of titanium dioxide is 600-900℃, and the main controlling factor of the oxidation rate of titanium alloy is the diffusion rate of oxygen ions passing through the oxide film within this temperature range.Second, the main influencing factors of oxidation rate are explored based on the titanium alloy oxidation kinetics model established according to Fick’s first law and the Arrhenius formula, and the influence of each factor on oxidation rate is determined by analyzing the titanium alloy oxidation kinetics model with MATLAB. The results show that the main influencing factors of the oxidation rate of titanium alloy are oxidizing temperature, oxygen concentration and pressure, fineness of grains, and oxide film thickness. The oxidation rate of titanium alloy can be accelerated by improving the above factors with exception to the oxide film thickness, as increasing oxide film thickness will decrease the oxidation rate of titanium alloy.Then, a test platform of the cutting technique under oxygen-enriched atmosphere is set up. The cutting parameters are optimized with the finite element simulation software Deform 3D to control the cutting temperature within the optimum temperature range. Cutting tests are conducted under different cutting parameters and oxygen-enriched environments, and varying composition, thickness, surface appearance and surface grains of the titanium alloy’s finished surface oxide film. The influences of cutting temperature, oxygen concentration and fineness of grains on the oxidation rate are analyzed. The validity of the oxidation kinetics model is verified by comparing the test results and theoretical results. The results show that the cutting technique under oxygen-enriched atmosphere can significantly increase the thickness and compactness of the oxide film on the finished surface of titanium alloy. The influence rules of cutting temperature, oxygen concentration and fineness of grains on oxidation rate are found to be consistent between the test results and theoretical results, which validates the oxidation kinetics model.Lastly, the biocompatibility of machining titanium alloy surface under oxygen-enriched atmosphere is evaluated. The corrosion resistance of the finished surface is studied, the corrosion mechanism of titanium alloy in simulated body fluid is analyzed and the main factors that influence the corrosion resistance of titanium alloy are determined through simulated body fluid soaking tests and electrochemical corrosion tests. Cell behaviors such as adhesion, spreading, proliferation, differentiation and mineralization are observed, the bioactivity of the finished surface is studied, and regulation mechanism of the finished surface on cell behaviors is analyzed through in vitro cell culture. The results show that machining under oxygen-enriched atmosphere can significantly improve the corrosion resistance of titanium alloy, and facilitate protein absorption with micro/nanometer composite structures formed on the surface. This also has a good control effect on cell behaviors such as adhesion, spreading, and proliferation, thus prominently improving the biocompatibility of biomedical titanium alloy implants.更多还原