LiF-NaF-KF熔盐中石墨基体上电沉积TiB2镀层的研究

Study on electrodeposition of TiB2 coatings on graphite substrate in LiF-NaF-KF molten salts

通过直流电沉积技术在LiF-NaF-KF熔盐体系中，以K2TiF6和KBF4作为活性物质在石墨基体上制备了晶粒细小、裂纹少、孔隙率低、表面平整和基体结合良好的TiB2镀层。研究表明，当电流密度为0．4～0．8A／cm^2，能够得到TiB2镀层。随着电流密度的增加，浓差极化作用逐渐显著，带来的负面影响是镀层边角效应也逐渐明显，这使得厚度均匀性下降；但过电位的增加又会导致镀层晶粒变得更为细小，这就削弱甚至足以弥补浓差极化对镀层表面平整度造成的负面影响，结果就是平整度随电流密度增加而得以改善。综合考虑，适宜的电流密度应控制在0．6A／cm^2，在该条件下，涂层由相对纯净的TiB2组成且表现出强的（110）面择优取向。涂层横截面上硬度分布范围为2986～3056HV0.1，表明涂层比较致密均匀。

Highly quality TiB2 coatings were obtained by the continuous current electrochemical techniques in LiF-NaF-KF electrolytes containing K2TiF6 and KBF4 as the electrochemically-active components. The research results indicated that TiB2 can be deposited when the current density ranges from 0.4 to 0.8 A/cm^2, and with the increasing of the current density, the role of concentration polarization gradually become prominent, which makes irregular distribution of current on the graphite cathode more and more evident. As a result, the thickness uniformity correspondingly decreases. However, the increasing of the over-potential makes grains get finer, which weakens or even makes up the negative effect of concentration polarization on surface flatness of coatings. So with the increasing of the current density, the surface flatness of coatings improves. Based on the comprehensive consideration, the suitable current density is fixed at 0.6 A/cm^2. At this condition, the coatings are composed of relatively pure TiB2 and show the strong preferred orientation of （001） plane. The microhardness of the coatings ranges from 2986HV0.1 to 3056HV0.1 and TiB2 coatings, which indicates the coatings are relatively compact and uniform.