Evaluation of the transformed layer of DLC coatings after sliding in oil using spectroscopic reflectometry
Evaluation of the transformed layer of DLC coatings after sliding in oil using spectroscopic reflectometry
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使用光谱反射法评估 DLC 涂层在油中滑动后的转化层
DOI：
10.1016/j.triboint.2013.01.010
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
M. Fujita
中科院分区：
文献类型：
--
作者：
K. Ohara;N. Masripan;N. Umehara;H. Kousaka;T. Tokoroyama;S. Inami;K. Zushi;M. Fujita
类金刚石（DLC）涂层以其低摩擦和高耐磨性不断受到人们的关注。转移或转化层由于循环摩擦导致sp2碳含量高，因此在环境空气中具有超低的摩擦系数。然而，关于这种层的报道很少，特别是在油润滑中的转化层，因为这种转化层可能太薄而无法定量测量。M. Kano和C. Matta用EFTEM研究了sp2碳层的厚度为3nm。应用光谱反射技术测量了DLC在油边界润滑条件下摩擦后磨痕转化层的厚度。本研究的目的是建立一种定量测量无氢DLC （ta-DLC）和两种类型的氢化DLC涂层中转化层厚度的方法。然后，我们明确了这些DLC涂层在油润滑下的摩擦模型，因为转化层是固体润滑膜。因此，我们观察到存在测量DLC变换层的最佳波长范围和光学模型。DLC的最佳波长范围为300 ~ 500 nm， DLC为无氢DLC，双层模型效果最佳。对于较厚且不透光的氢化DLC涂层，波长范围为600 ~ 800 nm，光学模型假设为单层模型。通过这些光学模型，我们观察到，在油边界润滑下，无氢DLC涂层的转化层厚度约为10-200 nm，而氢化DLC涂层的转化层厚度约为0-200 nm。通过对各种DLC涂层的转化层厚度和表面粗糙度σ的分析，我们发现，油边界润滑下DLC的摩擦系数是由转化层破裂的可能性决定的。这一结果有力地说明了DLC薄膜是一种能够实现自表面修饰的材料。我们相信本研究的结果可以作为DLC涂层表面设计的指导方针。
Diamond-like carbon (DLC) coatings continue to attract attention for their low friction and high wear resistance. The transferred or transformed layer, which has a high sp2carbon content induced by cyclic friction, results in an ultralow friction coefficient in ambient air. However, there are few reports on such layers, especially the transformed layer in oil lubrication, because this transformed layer could be too thin to be measured quantitatively. M. Kano and C. Matta reported the 3 nm thickness of a sp2carbon layer using EFTEM study. The spectroscopic reflectometry technique has been applied to measure the thickness of the transformed layer of the DLC's wear scar after friction under oil boundary lubrication. The purpose of this study was to develop a quantitative method for measuring the thickness of the transformed layer in hydrogen-free DLC (ta-DLC) and two types of hydrogenated DLC coatings. Then, we clarified the friction model of these DLC coatings under oil lubrication as the transformed layer was the solid lubricant film. Consequently, we observed that there were optimum ranges of wavelengths and optical models for measuring the transformed layer of the DLC. The optimum wavelength range was 300–500 nm, and the bi-layer model was the best for DLC1, which was the hydrogen-free DLC. For the thicker and un-transmissive coatings, which were hydrogenated DLC coatings, the ranges of wavelengths were 600–800 nm, and the optical model was hypothesized to be a single-layer model. From these optical models, we observed that the thicknesses of the transformed layers of the DLC coatings under oil boundary lubrication were approximately 10–200 nm in the hydrogen-free DLC and 0–200 nm in the hydrogenated DLC. From the analysis of the thickness of the transformed layer and surface roughness,σ⁎, of various DLC coatings, we observed that the friction coefficient of the DLC under oil boundary lubrication was determined by the possibility of breaking the transformed layer. This result strongly suggested that the DLC film was a material that realized self-surface modification. We believe that the results of this study could be developed as a guideline for designs of surfaces with DLC coatings.