超临界状态下镍基微细电化学复合沉积机理及方法基础研究

The micro-electrochemical deposition technology with functions of material fabrication and micro-forming plays an important role in the fabrication of micro components of Micro Electro Mechanical Systems (MEMS). Basing on the excellent diffusion and transfer properties of supercritical fluid(SCF), the basic research on mechanism, method and application of micro-electrochemical composite deposition of Ni matrix composites will be carried out. In which the particles with unique properties such as nano-diamond are used as composite additive. First, it will pay more attention to improving the basic problems under the supercritical state such as the generation and mass transfer characteristics of the composite solution, the mass transport in micron-scale intermittent and the composite deposition mechanism. Second, the theory and mathematical model related to the process of composite electrodeposition in the emulsion of SCF-CO2 composed of an electrolyte, a surfactant and dense CO2 will be constructed and studied by numerical analysis. Then, the influence rules of relevant process parameters on the microstructure, uniformity and mechanical properties of the micro-composite deposition layer were obtained. These process parameters consist of electric field distribution of the cathode, mass transfer state of the three-dimensional ions (particles) within the cathode template, electric criteria, and the content of surfactants or nano-additives. Finally, the equipment of micro-electrochemical composite deposition with supercritical fluids will be developed, and the high-performance, high-precision MEMS devices or surface coating of micro-parts will be electroformed successfully by using SCF-CO2 electroplating, which can provide a new way for the development of the fabrication technology of micro components of MEMS.

在微机电系统（MEMS）制造过程中，集材料制备与微细成形为一体的微细电化学沉积技术，承担着重要角色。利用超临界流体具有极好的扩散性和传递性能，以镍基电沉积为研究对象，性能独特的纳米金刚石等粒子为复合添加物，深入开展具有特殊性能要求的微细电化学复合沉积机理、方法与应用基础研究。重点解决超临界状态下电化学复合溶液的生成及其传质特性，微米尺度间歇内物质传输与复合沉积机理等基础问题；建立CO2流体、电解液及添加剂组成的超临界复合电沉积过程的有关理论和数学模型，并进行数值分析；研究、获得微细电化学复合沉积过程中，阴极电场分布与阴极模板内立体离（粒）子传质状态、过程电规准、表面活性剂和纳米添加物含量对微细复合沉积层微观结构、均匀性及力学性能等影响规律；研制超临界微细电化学复合沉积实验装置，复合沉积出高性能、高精度MEMS器件或微细零部件表面镀层，为MEMS制造技术的发展提供一种新方法。

传统的微细复合电沉积技术存在传质效果不佳，纳米颗粒之间易发生团聚和阴极氢气不能及时排除等技术难题，制得的复合铸层内部组织晶粒不够致密，内应力较大，铸层表面容易出现开裂，对微细电沉积即（LIGA技术技术的核心）而言，由于其沉积部分的特征尺寸仅有数微米到数百微米，阴极附近离子交换速度缓慢，沉积部分的电场、流场分布不均，电沉积层易产生麻坑、气孔等缺陷。本项目利用超临界流体具有极好的扩散性和传递性能，将性能特殊的纳米粒子（纳米金刚石颗粒、纳米碳化硅等）添加至超临界流体中，在超临界电化学复合液的生成与特性、复合沉积实验装置的研制，微细电化学复合沉积机理与工艺和微细零部件电化学复合沉积的应用基础等方面，创新性地开展了超临界状态下微细复合电沉积技术的机理以及应用基础研究。得出电流密度、复合添加量、超临界压力和超临界温度依次是影响超临界复合沉积的主要因素。获得相关超临界微细沉积规律和优化的工艺参数。复合沉积出高性能复合铸层，其显微硬度和耐磨性比普通复合铸层高50%以上，平均沉积电流密度可达9A/dm2，；在此基础上，复合沉积出MEMS器件。研发出相应超临界微细零部件复合电化学沉积装置。项目研究进一步拓展了复合电沉积技术，获得了具有自主知识产权的研究成果，为航空航天、信息控制等高端装备领域制备高性能微细零部件或表面镀层材料提供了一种新方法。