Department of Mining and Materials Engineering, McGill University , Montreal, QC H3A 0C5, Canada.
Department of Chemical Engineering and Materials Research Institute, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
ACS Appl Mater Interfaces. 2017 May 17;9(19):16704-16714. doi: 10.1021/acsami.7b03360. Epub 2017 May 3.
The origins of run-in and ultralow friction states of a sliding contact of hydrogenated diamond-like carbon (H-DLC) and sapphire were studied with an in situ Raman tribometer as well as ex situ analyses of transmission electron microscopy (TEM), Raman spectroscopy, and nanoindentation. Prior to ultralow friction behavior, H-DLC exhibits a run-in period. During the run-in period in dry nitrogen atmosphere, the transfer film was formed and its uniformity and thickness as well as structure were varied. The duration and friction behaviors during the run-in depended on the initial surface state of the H-DLC coatings. A comparative study of pristine and thermally oxidized H-DLC revealed the role of surface oxide layer on run-in friction and transfer film formation. Attainment of the ultralow friction state appeared to correlate with the uniformity and structure of the transfer film evolved during the run-in, rather than its final thickness. TEM cross-section imaging of the wear track and the counter surfaces showed a trace of nanocrystalline graphite and a thin modified surface layer on both rubbing bodies. The comparison of hardness and reduced modulus of the wear tracks and the unworn surfaces as well as the ex situ Raman spectra suggested the densification of the wear track surfaces. Combining the in situ and ex situ analysis results, a comprehensive model was proposed for the formation and structure of the ultralow friction sliding contact of H-DLC.
采用原位拉曼摩擦仪以及透射电子显微镜（TEM）、拉曼光谱和纳米压痕等的原位和非原位分析，研究了氢化类金刚石碳（H-DLC）与蓝宝石滑动接触的超低摩擦和极低速摩擦状态的起源。在表现出超低摩擦行为之前，H-DLC 会经历一个磨合阶段。在干燥氮气气氛中磨合期间，形成了转移膜，其均匀性、厚度和结构都发生了变化。磨合的持续时间和摩擦行为取决于 H-DLC 涂层的初始表面状态。对原始和热氧化 H-DLC 的对比研究揭示了表面氧化层在磨合摩擦和转移膜形成中的作用。达到超低摩擦状态似乎与磨合过程中形成的转移膜的均匀性和结构有关，而不是其最终厚度。磨损轨道和对摩面的 TEM 横截面成像显示在两个摩擦体上都有纳米晶石墨的痕迹和薄薄的改性表面层。对磨损轨道和未磨损表面的硬度和降低的模量以及非原位拉曼光谱的比较表明，磨损轨道表面的致密化。结合原位和非原位分析结果，提出了 H-DLC 超低摩擦滑动接触的形成和结构的综合模型。
