氯化物体系熔盐电沉积铬涂层工艺

Process of electrodepositing chromium coating in molten salt of chloride system

福岛核事故后,核燃料包壳Zr合金的Cr涂层表面改性成为研究热点,熔盐电沉积技术因能有效解决Cr层沉积时的析氢问题而受到关注,鉴于Zr合金在熔盐中易受腐蚀的特点,采用Ni作为过渡层解决Zr合金表面高质量Cr涂层的制备难题。为了系统研究Ni表面Cr涂层的熔盐电沉积工艺,本文在研究Cr涂层生长过程的基础上,研究电流密度、温度及Cr离子浓度对Cr涂层组织结构的影响,优选制备工艺并开展涂层性能测试。结果表明:增大电流密度、降低熔盐温度或减小Cr离子浓度可以细化涂层晶粒,提高涂层致密性和连续性,但同时易引发浓差极化,造成涂层质量恶化。在优选工艺下制得的Cr涂层由〈211〉取向的细等轴晶构成,硬度为(2.47±0.24) GPa,与Ni基体的结合力约为85 N,表面粗糙度为2.6μm。

After the Fukushima nuclear accident, the surface modification with Cr coating on nuclear fuel cladding Zr alloys becomes a research hotspot. Molten salt electrodeposition technology has attracted much attention because it can solve the problem of hydrogen evolution during Cr coating deposition effectively. In view of the corrosion characteristics of Zr alloy in molten salt, Ni is used as the transition layer to solve the preparation problem of high-quality Cr coating on the surface of Zr alloy. In order to research the effect of molten salt electrodeposition process of Cr coating on Ni surface systematically, the growth process of Cr coating was studied firstly. On this basis, the effects of current density, temperature and Cr(Ⅱ) ion concentration on the microstructure of Cr coating were characterized. Meanwhile, the preparation parameters of Cr coating were optimized, and the properties ware tested in this paper. The results show that increasing the cathode current density, lowering the molten salt temperature and reducing the Cr(Ⅱ) ion concentration will lead to refine the grain size of the coating,and improve the compactness and continuity within the scope of the study. But at the same time, these changes are easy to induce concentration polarization, causing serious deterioration of the roughness and compactness of the coating. The Cr coating is composed of fine equiaxed crystals with〈211〉orientation under the optimized process conditions, and the hardness is(2.47±0.24) GPa, the binding force is about 85 N and the surface roughness is 2.6 μm.