【作者】 卢立红；

【导师】 张静武； 沈德久；

【作者基本信息】 燕山大学 ， 材料学， 2012， 博士

【摘要】 本论文研究了Q235钢、工业纯钛和NiTi形状记忆合金（SMA）表面等离子体电解氧化（PEO）的工艺与机理，分析了获得陶瓷层的微观组织结构、相组成与性能，主要包括以下内容：采用热浸镀铝（HDA）和PEO相结合的方法，在Q235钢基体表面获得一层陶瓷层。用扫描电镜（SEM）观察了复合膜层的断面及表面形貌，用X-ray衍射仪（XRD）分析了陶瓷层的相组成，特别是使用透射电镜（TEM）对陶瓷层进行了观察和选区电子衍射；综合分析了陶瓷层的形成过程随PEO时间和电流密度的变化规律，在此基础上研究了陶瓷层向内外生长的比例关系，提出了膜的形成及表面现象与对应的电压区间的关系模型；研究了陶瓷层的硬度、耐磨性能、孔隙率和耐蚀性能；对Q235钢表面热浸镀铝层PEO的反应机理进行了分析。结果表明：（1）复合膜层由三层构成，由内向外依次为Fe-Al合金层、纯热浸镀铝层和PEO陶瓷层，各层之间达到了冶金结合，陶瓷层表面存在较多的孔洞和裂纹。随着PEO时间的延长，陶瓷层表面颗粒变大，重熔、凝固程度增加，孔洞增大。（2）陶瓷层主要由晶态Al₂O₃相组成，并含有一定量的非晶态相。晶态Al₂O₃相包括κ-Al₂O₃、θ-Al₂O₃和β-Al₂O₃，其中β-Al₂O₃相含量最少。随着PEO时间延长，非晶态相逐步向晶态相转变。κ- Al₂O₃的晶体尺寸分布范围较宽，小者不足100 nm，大者超过了500 nm，甚至超过了TEM衍射区尺寸，可获得纯单晶特征的衍射花样。（3）陶瓷层的总厚度、向外生长厚度和成膜速率均随着PEO时间的延长有一极大值，其出现的时间随着电流密度的增大而缩短。当电流密度为1.5A/dm²，PEO时间为12 min时，陶瓷层总厚度达到最大值，约为47.5μm。向内生长厚度均随着PEO时间的延长而增加。不断增加电流密度，陶瓷层逐步由向内生长为主转变为向外生长为主。（4）陶瓷层硬度达到了HV 1 300；当摩擦延长米为70 m时，其耐磨性能比淬火-回火45钢提高了2.3倍。耐NaCl溶液及海水的腐蚀能力远优于Q235钢基体。通过PEO处理，在工业纯钛表面获得一层陶瓷层。观察了陶瓷层的表面及断面形貌，分析了陶瓷层的相组成，研究了不同添加剂对陶瓷层耐蚀性能、表面形貌以及组成成分的影响，分析了工业纯Ti进行PEO处理的工艺性。结果表明：（1）工业纯Ti在含有硅酸钠、铝酸钠和磷酸钠的混合电解液中获得的陶瓷层表面较为平整，分布着若干蜂窝状、相互交错的微孔，不可见裂纹。陶瓷层与基体结合紧密。（2）在混合电解液中获得的陶瓷层主要由锐钛矿（anatase）型TiO₂相组成。（3）电解液中的元素参与了陶瓷膜层的生成过程。陶瓷层中除含有大量Ti和O元素外，还含有微量的Al、Si、P等元素以及电解液添加剂的元素如B、Ce等。（4）稀土元素Ce的添加，使陶瓷层中Al、Si、O、P的含量明显增多，陶瓷层耐10% H₂SO4溶液腐蚀的性能显著提高。采取表面去镍腐蚀前处理工艺与PEO相结合的方法，在NiTi SMA表面获得一层陶瓷层。对比研究了未进行去镍腐蚀、分别经硝酸溶液、H₂O:HNO₃:H₂SO₄=5:4:1（V）溶液和王水选择性腐蚀处理后NiTi SMA试样的表面形貌及其进行PEO处理的工艺性。分析了前处理工艺对陶瓷层表面形貌、成分以及相组成的影响。结果表明：（1） NiTi SMA直接进行PEO处理，工艺性很差，表面去镍腐蚀前处理工艺能够显著改善NiTi SMA的PEO工艺性。在常温王水中选择性腐蚀10 min后获得的试样，进行PEO处理的工艺性最好，电流—时间曲线与工业纯Ti在同一PEO条件下最为接近。（2）适合于NiTi SMA进行PEO处理的稳定电解液成分为：磷酸钠5 g/L，铝酸钠5 g/L，硅酸钠5 g/L，二氧化钛1 g/L，双氧水5 mL/L。（3） NiTi SMA表面陶瓷层的主要成分为Ti、Al、O、P、Si等元素，相组成主要是锐钛矿型TiO₂相。延长在王水中的去镍选择性腐蚀时间，陶瓷层中锐钛矿型TiO₂相增多。（4）经王水腐蚀10 min的NiTi SMA试样，其腐蚀均匀性最好，出现了类似海绵状的腐蚀结构。腐蚀后的NiTi SMA进行PEO处理，获得的陶瓷层质感很好，表面存在较多蜂窝状微孔，能够增强羟磷灰石等生物活性剂的附着能力。更多还原

【Abstract】 Using the methods of plasma electrolytic oxidation （PEO）, the structures，the phasecompositons and the properties of the ceramic coatings on Q235 steel, industrial pure Tiand NiTi shape memory alloy （SMA） were studied in this thesis. The main contents areas follows:Firstly, a hybrid method of hot-dipping aluminum （HDA） and PEO was employed tofabricate composite ceramic coatings on the surface of Q235 steel substrate. Thecross-sectional microstructure and surface morphologies were investigated with scanningelectron microscopy （SEM）. The X-ray diffraction （XRD） was used to analyze the phasecompositon of the ceramic coatings. Particularly, the transmission electron microscopy（TEM） was used for selected area electron diffraction and to observe the structure of theceramic coatings. The evolutions of PEO behaviors changing with PEO time and currentdensity of the HDA coatings on Q235 steel substrate were analyzed. And on this basis,the ratio of the ingrown and outgrown coatings was investigated, the model of therelationship between the film formation, the surface phenomena of the coatings and thecorresponded voltage region was given. The cross-sectional microhardness, the wearresistance, the porosity and the corrosion resistance of the HDA-PEO treated specimenswere studied. At last, the film formation mechanism during the PEO process of the HDAcoatings on Q235 steel substrate was analyzed. The results indicate that: （1） Thecomposite coatings obtained by this hybrid method consists of three layers from inside tooutside, i.e. Fe-Al alloy layer next to the substrate, aluminum layer between the Fe-Allayer and the ceramic coatings which is as the top exterior layer. Metallurgical bondingwas observed between every of the two layers. There are many micro-pores andmicro-cracks in the PEO coatings. The grain size is biger and biger, the re-melting andsolidification of the grains is severe more and more and the size of the pore in theceramic coatings increases gradually with the increasing of the PEO time prolonged. （2）The phase composition of the ceramic coatings is mainly composed of crystal Al₂O₃oxides and a certain quantity of amorphous phase. The crystal Al₂O₃phase includesκ- Al₂O₃,θ- Al₂O₃andβ- Al₂O₃. Compared with the others, theβ- Al₂O₃content is the least.The amorphous phase convertes to the crystal phase gradually with the PEO timeprolonged. The grain size of theκ- Al₂O₃crystal is quite non-uniform. The smallest oneis less than 100 nm and the largest one is more than 500 nm. One of the largest grains isover the TEM diffraction zone and the single crystal diffraction patterns can be obtained.（3） The total thickness, outgrown thickness and growth rate have maximum values withthe PEO time prolonged. The time when the maximum value appears decreases with thecurrent density increasing. In our experiement conditions, the maximum value of the totalthickness is about 47.5μm and the corresponding current density and the PEO time are1.5A/dm²and 12min respectively. The ingrown thickness of the ceramic coatingsincreases with the PEO time prolonged at any current density. The ingrown dominantturns to outgrown dominant little by little with the current density increasing. （4） Thehardness of the ceramic coatings is about HV1300. When the wearing sliding distance is70m, the wear resistance of the PEO samples is about 2.3 times higher than that of theheat treated 45 steel. The corrosion resistance of the PEO coatings is much better thanthat of the Q235 steel when immersed in the NaCl solution or in the sea water.Secondly, the ceramic coatings was deposited on the surface of the pure industrialtitanium by PEO method. The surface and cross-sectional morphologies of the ceramiccoatings were observed with SEM. The phase composition of the ceramic coatings wasanalyzed with XRD.The influence of several different additions on the corrosionresistance, the surface morphology, the component and the phase compositon of theceramic coatings was investigated. The PEO manufacturability of the pure industrialtitanium was studied. The results show that: （1） The surface of the ceramic coatingsobtained in the mixed electrolyte containing Na2SiO3, NaAlO2and NaH2PO4is even.There are many honeycomb-like and over lap micro-pores and invisible cracks in it. Thebongding of the ceramic coatings and the substrate is strong. （2） The phase compositionof the ceramic coatings obtained in the mixed electrolyte is mainly composed of anatase.（3） The element in the electrolyte takes part in the film formation. Besides large amountof Ti and O elements, there are little amount of Al, Si, P elements and the elements fromthe additons in the electrolyte such as B, Ce, et al. in the ceramic coatings. （4） The addition of Ce makes the contents of the Al, Si, O and P elements increase significantlyin the ceramic coatings, and the corrosion resistance of the ceramic coatings improveremarkablely.Thirdly, the ceramic coatings was obtained on the NiTi SMA substrate with PEOafter the pretreatment of selective delloying to remove the Ni from the surface of NiTiSMA. The PEO surface morphologies and the PEO manufacturability were studied of thesamples which were not pretreated and pretreated by immersed in the solutions of HNO3,H₂O:HNO₃:H₂SO₄=5:4:1 （V） and aqua regia respectively. The influence of thepretreatment technology on the surface morphologies, the ingredient and the phasecompositions of the ceramic coatings were analyzed. The results indicate that: （1） ThePEO manufacturability of the samples not pretreated by selective delloying was very bad.The selective delloying pretreatment technology can improve the PEO manufacturabilityof NiTi SMA prominently.When the dealloying time is 10 min in aqua regia at roomtempreture, the PEO manufacturability of the NiTi SMA is best and the curve ofcurrent-time is most close to that of the pure industrial titanium at the same experimentalconditions. （2） The ingredient of the electrolyte which is suitable for PEO of the NiTiSMA is as follows: NaH₂PO₄5g/l, NaAlO₂5g/l, Na₂SiO₃, TiO₂1g/l and H₂O₂5ml/l. （3）The main elements of the ceramic coatings on NiTi SMA are Ti, Al, O, P and Si. Thephase compositon is mainly composed of anatase. And the quantity of the anataseincreases with the selective delloying time prolonged immersed in aqua regia solutions.（4） The corrosion uniformity of the NiTi SMA is best when the delloying time is 10 minimmersed in aqua regia solutions and the spongy surface morphology can be seen withthe SEM. The texture of the PEO ceramic coatings on the NiTi SMA after delloying isdesired. There are many micro-pores in the honeycomb-like coatings which is beneficialto the adherence of the hydroxylapatite.更多还原