【作者】 田海燕；

【导师】 朱荻；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 纳米复合镀层由于具有优异的物理机械性能而受到广泛的研究与关注。在目前的研究中,主要是通过纳米粒子与基质金属的共沉积来制备纳米复合镀层,由于共沉积工艺所制备纳米复合镀层中的微粒含量极低,纳米粒子的独特性能未能得到充分发挥,复合镀层的性能难以得到更为有效的提高。为充分发挥纳米粒子的性能,制备具有更高微粒含量的纳米复合镀层,本文提出了采用电泳-电沉积制备纳米复合镀层的新工艺。具体为:首先在基体表面电泳沉积均匀分布且良好分散的纳米粒子,然后在微粒孔隙之中电沉积基质金属,以基质金属镶嵌纳米粒子而获得纳米复合镀层。采用电泳-电沉积工艺制备纳米复合镀层的微粒体积含量在15%~60%之间,微粒含量的显著提高使得镀层中纳米粒子的独特性能得以充分发挥。本文的主要研究内容及其结论如下:1.开展了纳米粒子的电泳沉积研究。系统研究了电泳沉积参数对电泳沉积量及沉积层中纳米粒子分散状态的影响,优选了对纳米Al2O3粒子在乙醇溶液中具有解团聚作用的分散剂,初步实现了均匀分布且具有良好分散的纳米粒子电泳沉积层的制备。2.研究了电泳-电沉积工艺制备纳米复合镀层的工艺过程。通过分析金属电沉积过程中纳米粒子分布状态的变化,提出了电沉积过程中纳米粒子存在着被扰动与再沉积的现象;系统分析了电泳-电沉积工艺中各工艺参数对纳米复合镀层微粒含量及其分散状态的影响,并研究了各工艺参数组合下复合镀层所能达到的最大厚度。3.对电泳-电沉积纳米复合镀层的表面形貌、组织成分及微观结构进行了测试与分析。研究了主要工艺参数对纳米复合镀层微观形貌的影响;以各微区内微粒含量的均方差为评价指标,采用正交试验研究了影响镀层中纳米粒子分布均匀性的主要因素,并就纳米粒子对基质金属择优取向的影响,以及纳米复合镀层的微观组织结构进行了分析。研究表明,电泳液微粒浓度与电沉积阴极电流密度是影响镀层中纳米粒子分布状态的主要因素;经过良好分散的纳米粒子可以显著细化基质金属晶粒,复合镀层的表面平整,组织致密均匀,弥散分布的纳米粒子与基质金属之间有着良好的结合,纳米粒子的存在对基质金属的择优取向产生了明显影响。4.对纳米复合镀层的显微硬度、耐磨性、耐蚀性及其与基体的结合性能进行了研究。结果表明,纳米粒子的强化作用使得纳米复合镀层的显微硬度与耐磨性能均有明显提高,其磨损形式主要是以磨料磨损为主;与纯镍镀层相比,复合镀层在各类腐蚀介质中的腐蚀凹坑更为细小和均匀,镀层表面的腐蚀均匀性有所提高;纳米复合镀层与基体的结合强度同镀层中的微粒含量有关,当微粒含量在一定范围内时,复合镀层的结合强度优于纯金属镀层的结合强度。更多还原

【Abstract】 Nano-composite coatings are widely studied because of its excellent physical mechanical properties. The nano-composite coating is prepared mainly by nanoparticles codeposition with matrix metal at present. Because only a few nanoparticles were embedded in the coatings by this method, the properties of the coatings is unable to be improved significantly.In this dissertation, a new technique, electrophoretic-electrochemical deposition, was proposed to produce nano-composite coatings with high content of nanoparticles. A uniform film of nanoparticles was first electrophoretically deposited on a substrate, the matrix metal was then electrodeposited onto the substrate covered with the film of these nanoparticles. By adopting this method, the nano-composite coatings with 15~60vol% of nanoparticles can be obtained. The properties of the coatings can be improved efficiently because plenty of nanoparticles exists in the coatings.The main researches and conculsions are given as follows:1. The researches on electrophoretic deposition of nanoparticles were carried out. The influence of the process parameters on the deposition weight and dispersion state was studied, the deposition layer with uniform distribution and well dispersed nanoparticles was produced by optimizing the dispersant.2. The process of electrophoretic–electrochemical deposition was studied. Through analyzing the changes of the nanoparticles distribution state, a phenomenon was observed that nanoparticles was disturbed and redeposited at the electrodeposition process. The effects of the parameters on the particle content and the nanoparticles dispersion state were systematically analyzed, and the maximum thickness of the composite coatings was studied.3. Surface morphology, component, and microstructure of the nano-composite coatings were examined. The effects of process parameters on the micro-morphology of the nano-composite coatings were investigated. With the mean square deviation of the particle content in the micro-region as an evaluating index, the effects of the parameters on the distribution uniformity of the particles were studied by orthogonal test. Meanwhile, the crystal orientation of matrix metal and microstructure of nano-composite coatings were examined. The results indicated that, the main factors that influenced the particles distribution state were the concentration of nanoparticles in electrophoretic bath and the current density at the electrodeposition process. The nano-composite coatings exhibit a smooth surface and compact microstructure. Nanoparticles are dispersed inside the metallic matrix and combined with the metallic matrix closely. In electrodeposition process, nanoparticles affect the preferred orientation of matrix metal remarkably.4. The properties of the nano-composite coatings, such as microhardness, wear resistance, corrosion resistance and adhesion strength were evaluated. The results showed that the microhardness and wear resistance of the nano-composite coatings were significantly increased, and the major wear pattern under dry friction conditions was abrasive wear mechanism. Compared with pure Ni coating, the corrosion pits of the nano-composite coatings become smaller and more uniform. The bonding strength is related to the particle content, when the particle content is in a certain ratio, adhesion strength of the nano-composite coatings is better than the pure metallic coating.更多还原