SiCp/Al复合材料微弧氧化陶瓷膜制备及成膜机理研究

Friction surface scratches are an important problem which should be solved urgently for the application of SiCp/Al composites brake disc. To fabricate ceramic coatings on the surface of SiCp/Al composites is one of the effective methods to solve the above problem. Even though it is difficult to fabricate ceramic coatings with good properties on SiCp/Al composites by micro-arc oxidation (MAO) method because of the existence of nonconductive second-phase SiC particles, the ceramic coatings on SiCp/Al composites have been successfully fabricated with sodium aluminate electrolyte with MAO method by our research group. Whereas the characteristics of the ceramic coating, such as scratch resistance, should be improved. Based on the above achievement we will research on MAO process parameters in order to improve the quality of the ceramic coating and increase scratch resistance. The SiC particle morphology and structure of ceramic coating changes will be studied, to clarify the evolution mechanism of SiC particles during MAO process; The transient characteristics of the plasma micro arcs during the MAO process are studied by high-speed imaging system, then combined with capacitance-resistance simulation model of ceramic films influencing factors of plasma micro arcs are investigated by the electrical simulation technology of MAO. The variation of the ceramic coating properties during the MAO process is also discussed. The relationship between process parameter, the plasma micro arcs and ceramic coating properties is determined, and the formation mechanism of ceramic coating on SiCp/Al composites is illustrated. The research has important academic value to enrich the micro-arc oxidation theory and also has engineering significance on promoting the application of SiCp / Al composites on lightweight brake disc.

摩擦制动引起的制动盘表面划伤是SiCp/Al复合材料制动盘亟待解决的问题，采用微弧氧化技术在复合材料表面制备陶瓷膜是解决划伤的有效手段，但材料中不导电的SiC颗粒阻碍微弧氧化起弧。项目组在采用铝酸钠电解液已成功制备出SiCp/Al复合材料微弧氧化陶瓷膜的基础上，对其微弧氧化工艺进行研究，改进陶瓷膜质量，提高膜层的抗划伤性能；通过分析SiC颗粒形态和陶瓷膜组织结构变化，阐明SiC颗粒的演变及其成膜机制；利用高速成像系统采集微弧氧化过程中等离子微弧特征的动态变化，结合陶瓷膜的电容-电阻仿真模型，分析等离子微弧动态变化的影响因素，系统地研究微弧氧化工艺参数对微弧特征变化以及等离子微弧动态变化对陶瓷膜特性的影响，明确工艺参数、等离子微弧特征、陶瓷膜特性之间的关系，揭示复合材料微弧氧化的成膜机理。本项目研究对丰富微弧氧化理论具有重要学术价值，对推动SiCp/Al复合材料轻质制动盘的应用具有工程意义。

轻质低噪SiCp/Al复合材料制动盘制动过程中摩擦面的划伤和犁沟是亟待解决的问题，采用微弧氧化技术在SiCp/Al复合材料表面制备陶瓷膜是解决表面划伤的有效手段。因此，课题针对不导电第二相SiC颗粒导致的SiCp/Al复合材料微弧氧化处理技术的差异性和特殊性，采用试验及微观分析、仿真计算和摩擦磨损试验，开展了复合材料微弧氧化成膜工艺及摩擦磨损特性、SiC颗粒在微弧氧化过程中的演变机制以及复合材料微弧氧化成膜机理研究。.SiCp/Al复合材料陶瓷膜的内层主要由刚玉结构的α-Al2O3组成，陶瓷膜致密硬度高，在距离膜基界面20μm处达到了最大值1406Hv；而陶瓷膜的外层主要由γ-Al2O3和莫来石相组成，陶瓷膜比较疏松，硬度降低。陶瓷膜与闸片材料之间的磨损机制是以粘着磨损和磨粒磨损为主的混和磨损。.SiCp/Al复合材料在不同电解液中的成膜特性研究表明，SiCp/Al复合材料在铝酸盐电解液中能迅速正常起弧。而在硅酸盐溶液、磷酸盐和硼酸盐溶液中不能正常起弧。.SiC颗粒的演变研究表明，碳化硅分解驱动力来自于两个方面，一是碳化硅颗粒外表层在强电场作用下被击穿发生氧化反应，导致SiC分解生成SiO2，C变成CO2逸出；二是基体中铝发生微弧放电时产生的高温高压环境，为SiC分解提供能量支持。没有分解完全的SiC颗粒被铝的氧化物包覆并残留在陶瓷膜内部。因此，SiC颗粒在复合材料微弧氧化过程中以先分解后包覆的模式演变。SiC颗粒改变了陶瓷膜生长方向，SiCp/A356复合材料以向外生长为主，向内生长为辅，陶瓷膜生长表现为明显的氧化物沉积过程。.此外，利用高速摄像机研究了微弧氧化放电现象，研究表明，在一个脉冲期间内，等离子体微弧的存在时间约为7ms，总共产生约5250个微弧，微弧分布密度为1.5×105个/m2，单个微弧能量为2.63×10-3J。随陶瓷膜厚度增加，微弧尺寸增大、寿命延长，而分布密度减少。.本课题研究工作对丰富微弧氧化理论具有重要的学术价值，对提高SiCp/Al复合材料耐磨性具有实用价值，为SiCp/Al复合材料在城市轨道列车轻质制动盘上的应用奠定了理论和技术基础。