【作者】 李乐；

【导师】 姚斌；

【作者基本信息】 吉林大学 ， 应用物理， 2012， 博士

【摘要】 微弧氧化（MAO）技术是一种阀金属表面改性技术，该技术通过微弧放电方式在材料表面原位生长一层致密的氧化膜（MAO膜），以达到保护内部金属的目的。因其具有高硬度、耐磨损和耐腐蚀等方面的优异特性，一直以来都受到研究者的高度关注。近年来，随着MAO技术的发展和MAO膜新特性被不断挖掘，使得MAO技术的应用不仅局限于材料的表面防护，也扩展到环保，医学和光学领域，成为多领域交叉学科研究的重要前沿课题之一。近年来，国内外很多科研机构开展了微弧氧化膜的制备与特性研究工作，虽然取得很大的进展，但是，目前，人们对影响MAO膜生长和性能的因素、规律和机制还缺少完整的认识，从而严重阻碍了MAO技术的应用和发展，成为MAO研究的重要科学问题之一。因此，通过实验寻找影响MAO膜质量和特性的内在因素、规律和机制，优化MAO膜的制备工艺，对于MAO技术的应用和发展都具有重要的意义。本文以钛基MAO膜为研究对象，对影响MAO膜结构、质量、力学、电化学和电致变色性能的因素、规律和物理机制进行了研究，希望通过优化工艺参数，实现对MAO膜的可控生长，制备出综合性能优异的功能氧化膜。本论文以添加不同浓度氢氧化铝胶体的铝酸盐、磷酸盐和硅酸盐溶液为处理液，利用MAO技术的恒压模式与恒流限压模式在金属钛基上生长出MAO膜。实验表明，通过增加氢氧化铝胶体浓度和增大阳极脉冲电压，可以分别制备出金红石-锐钛矿混合相结构、单一金红石相结构、金红石-钛酸铝混合相结构的MAO膜层。对膜层生长特性与微观形貌的研究表明，单一金红石相二氧化钛结构的MAO膜具有更好的膜层特性。并由此总结出通过工艺参数调控膜层晶相组成和膜层质量的规律。研究发现，处理液中氢氧化铝胶体的添加对膜层的晶相结构起决定性作用。作为大分子团，氢氧化铝胶体颗粒在溶液中阻碍溶液中其它较大离子通过微弧放电进入膜层，保证了膜层中仅含有钛和氧两种元素。另外，它会阻碍微弧放电区域热量的传递，造成反应局部温度升高，使二氧化钛形成时处在金红石相的热力学稳定区，导致膜层中金红石相二氧化钛含量增加或膜层完全由金红石相二氧化钛构成。但是，如果阳极脉冲电压过高，则会造成氢氧化铝分解并进入膜层，使膜层中含有部分钛酸铝成分。所以，氢氧化铝胶体的浓度和阳极脉冲电压是调控膜层晶相组成的关键。对MAO膜的力学性能的测试表明：单一金红石相MAO膜层的硬度最优，硬度随膜层二氧化钛晶粒尺寸的增加而增大。膜层具有较高的膜基结合强度，并且弹性模量可达167GPa，是目前国内外报道中的最高值，这使膜层具有良好的抵抗外力冲击能力与耐磨损性能。对膜层耐腐蚀特性的评估表明，膜层腐蚀主要以钛金属的腐蚀为主。相对于混合相膜层，单一金红石相膜层具有较好的耐腐蚀性能。这是由于膜层厚度增加且膜层中放电微孔直径减小所造成的。其中膜层中微孔的特性对膜层耐腐蚀性影响较大，原因在于腐蚀液在微孔中流动性降低，导致腐蚀过程减缓，有利于膜层耐腐蚀特性的增强。在PH2.0的盐酸溶液中对单一金红石相膜层基底施加负向电压，会使膜层颜色发生改变，由浅灰色转变为藏青色。并且在电压撤除或在基底施加正向电压情况下，膜层会恢复原来的颜色。光谱测试表明，这种电致变色可归因于在外电场作用下膜层的反射光强度随波长的增加而减弱的结果。循环伏安曲线测量证明这种电致变色过程可稳定的多次循环，而且光学特性几乎不变。这种电致变色现象，可以归因于在外加电场作用下，氢离子注入到二氧化钛晶格，在禁带中产生杂质能级，改变了膜层的光吸收特性。综上所述，通过调整处理液中氢氧化铝胶体的浓度和阳极脉冲电压，实现了对MAO膜晶相成分的调控，获得了具有高弹性模量、耐磨、耐腐蚀的单一金红石相MAO膜，并在PH2.0盐酸溶液中观察到MAO膜具有稳定的电致变色特性。更多还原

【Abstract】 Micro-arc oxidation (MAO) is a valve metal surface modification technology. Bymicro-arc discharge, a layer of dense oxide coating (MAO coating) is prepared in theoriginal location to protect the interior metal. Because of its high hardness, excellentabrasion and corrosion properties, MAO technology has been payed high attention byresearchers for a long time. In recent years, with the development of MAO technology,new features of MAO coating have been discovered constantly. Applications of MAOtechnology have not only confined to the surface protection of materials, but also extendto environmental protection, medical and optical fields. MAO technology has becomingone of the most important topics in the forefront of the multi-field cross-disciplinaryresearch.In recent years, many scientific research institutions have carried out the research ofpreparation and characterization on MAO. Although many progresses have been made,however, lack of systemic theory on coating growth law and performance factorsmechanisms limited the application and development of MAO technology, which hasbecame one of the most important scientific problems about MAO study. Therefore, it isvital to application and development of MAO technology that not only by figuring out theinternal factors, laws and mechanisms which can affect the quality and characteristics ofMAO coatings, but also by optimizing the preparation technology of coating. In this work,the factors, laws and physical mechanisms on the influence of coating structure, quality,mechanical, electrochemical and electrochromic properties of titanium-based MAO coating were studied in this thesis. We hope to control the growth of MAO coating andprepare a kind of coating which has good combination property by optimizing thetechnological parameters.Adding different concentrations of aluminate, phosphate and silicate solution ofaluminum hydroxide gel as electrolyte, MAO coatings is grown on a titanium substrateby using the constant voltage mode and constant current limiting voltage mode of MAOtechnology. The experiments show that by increasing the concentration of aluminumhydroxide gel and the anode pulse voltage, the phase structure of the coatings preparedare rutile-anatase mixed phase, single rutile phase and rutile-aluminum titanate mixedphase respectively. Studies of growth characteristics and morphology of the coating showthat the coating of single rutile phase has better properties. And based on the abovestudies, we can sum up the law of the coating crystalline phase and coating quality byregulating the technological parametersStudy shows that the aluminum hydroxide gel in the electrolyte plays a decisive roleon the formation of coating crystalline structure. As a kind of macromolecular group,aluminum hydroxide colloidal particles can hinder other large ions in electrolyte movingto the micro-arc area or entering into the coating, which ensures that the coating onlycontains titanium and oxygen. Also, it can hinder the heat transfer from micro-arc area tothe electrolyte, causing the temperature of this area increased. All these factors leads theformation of titanium dioxide to be in the rutile phase thermodynamically stable zone,resulting in the increase of the rutile phase titanium dioxide content in the coating or thecoating being entirely composited by the rutile phase titanium dioxide. However, if theanode pulse voltage is extensive high, it will cause the aluminum hydroxide decomposesand enters the coating, making the coating contains some aluminum titanate composition.Therefore, the concentration of aluminum hydroxide gel and the anode pulse voltage arethe keys to regulation the crystalline phase of the coating.Mechanical properties tests of the MAO coatings show that the single rutile phaseMAO coating has the best feature on coating hardness. Coating hardness increases withthe increase of the titanium dioxide grain size of the coating. The coating also has a goodcoating-substrate binding strength and elastic modulus. The elastic modulus is up to167GPa which is the highest one in the current of domestic and international report. These properties make the coating having good capacity of resisting external shocks andabrasion resistance.Coating corrosion resistance test shows that, the single rutile phase MAO coatinghas better corrosion resistance than the mixed-phase MAO coating. This is caused by theincreased coating thickness and decreased discharge micropore diameter of the coating.In which, the characteristics of the micropores effect the coating corrosion resistancemore significantly. Because the liquidity of etching solution reduced in the micropore, thecorrosion process slows down, which enhance the coating corrosion resistance.In the PH2.0acid solution, applying a negative voltage, the single rutile phase MAOcoating changes its color from light gray to navyblue. When the voltage is removed or aforward voltage is applied on the coating, the color of the coating will recover its originalcolor. The spectra test shows that this electrochromic is attributed to the reflected lightintensity of the coating weakened with the wavelength increase under the external electricfield. Cyclic voltammetry test proves the the electrochromic process can be reversedmany times, and the coating optical properties are almost unchanged. This electrochromicphenomenon can be attributed to the hydrogen ion injecting into the titania lattice, whichresulting in impurity level emerges in the titanium dioxide band gap and changes theoptical absorption propertie of the coating.In summary, phase composition of the MAO coating is regulated by theconcentration of aluminum hydroxide gel in electrolyte and the anode pulse voltage. Theprepared coating has single rutile composition, which have good mechanical andcorrosion resistance properties. The coating has a reversible electrochromic property inPH2.0hydrochloric acid.更多还原