熔盐电化学法制备高熔点金属碳化物涂层的研究

Niobium and tantalum carbides coatings are widely applied in fields of electronic, aerospace, chemical, and military industries, because of their unique properties such as high hardness, good friction performance, high temperature resistance, and excellent corrosion resistance. PVD and CVD are the most frequently used methods to prepare the carbides coatings, in which complicate apparatus, tough conditions are usually employed. Especially, carbides coating with high adhesion to substrate is still a big challenge because of high intrinsic stress within the coating, which generates from relatively high temperature in these processes. The proposal focuses on fabrication of continuous and uniform niobium carbide and tantalum carbide coatings on the modified tantalum, niobium substrates by a joint process combining elecro-deoxidation and electro-deposition in molten salt. In this work, carbonate ions are used as carbon source, and the molten salt is employed as electrolyte. Some fundamental issues will be investigated, such as the optimized conditions for oxidation and electro-deoxidation of the metal substrates, mechanism of the cathodic process of carbon deposition from carbonate ions and in-situ carbonization with refractory metals. Chemical bonds could be formed between carbide coatings and substrates during the joint process, which help to enhance adhesion of the coatings effectively. The cathodic process will be investigated by the electrochemical methods. The doped carbide coatings will be prepared in the molten salt with some additives, which can improve properties of the coatings. Based on the results of investigations, the joint process will be optimized and refractory metals carbide coatings will be prepared under the controlled conditions. The aim of this research is to supply the scientific fundamentals and prototype technology for preparation of carbide coatings by a low-cost, simple and environmentally friendly method.

碳化铌、钽涂层具有高硬度、摩擦性能好、耐高温、抗腐蚀等优良性能，被广泛应用于电子、航天、化工和军工等领域。目前，制备碳化物涂层常用CVD和PVD技术，但普遍具有沉积设备复杂，工作条件苛刻等问题。特别基体的承受温度通常较高，制备的涂层有较大的内应力，使碳化物涂层的附着强度有待提高。本研究课题以熔融盐为介质，碳酸盐为碳源，采用熔盐电脱氧、电化学碳沉积两段式方法在表面改性的高熔点金属铌、钽基体上沉积碳化铌、碳化钽涂层。考查基体表面氧化、电脱氧和电化学碳沉积等过程的适宜条件；研究碳酸根离子的沉积过程以及沉积碳与基体表面电脱氧产物原位反应机理等基础问题；通过两段式方法在涂层和基体之间形成化学键结合，增强碳化物涂层的附着强度；采用电化学分析技术研究制备碳化物的电极反应过程；在熔盐中加入添加剂对碳膜进行掺杂，优化涂层的性能。实现对两段式电化学反应过程的强化，以及对碳化物涂层组成、形貌和结构的有效控制。为经济、便捷和环境友好地制备高熔点金属碳化物涂层提供科学依据和技术原型。

本研究以碱金属或碱土金属卤化物为介质，相应的同阳离子碳酸盐为碳源，分别在高熔点金属Ta、Nb表面制备碳化物涂层材料。研究分析了碳化物涂层的形成历程、反应机制，讨论反应过程中的动力学机理；考查了反应过程中的影响因素。通过氧化-电化学脱氧等技术修饰基体表面形貌，在动力学上促进了碳化物涂层的形成。此外，也为形成基体和涂层之间化学键的连接、提高涂层的性能提供有利条件。利用XRD、SEM结合EDS、XPS、TEM以及涂层表面附着力划痕仪等手段分析碳化物涂层的形貌、物相、结构以及机械性能。研究尝试使用碳化物为中间层，制备了基体-碳化物-碳多层复合材料。在此基础上，对研究项目进一步延伸，以高熔点金属氧化物和碳为原料，制备了NbC、Fe-NbC、Ni-TiC/TaC等碳化物和金属基碳化物粉体材料，分析反应过程机理，并表征了材料的性质和性能。为熔盐电化学法制备高熔点碳化物涂层、粉体及相关功能材料提供重要的理论依据。