Distinct effects of endogenous hydrogen content and exogenous hydrogen supply on superlubricity of diamond-like carbon
Distinct effects of endogenous hydrogen content and exogenous hydrogen supply on superlubricity of diamond-like carbon
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DOI：
10.1016/j.carbon.2022.11.011
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发表时间：
2022-11-18
期刊：
影响因子：
10.9
通讯作者：
Kim, Seong H.
中科院分区：
文献类型：
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作者：
Jang, Seokhoon;Kim, Seong H.
氢化类金刚石碳（HDLC）由于其超润滑性而作为固体润滑涂层引起了极大的兴趣。然而，根据氢（H）含量或sp2/sp3碳比，HDLC表现出显著不同的摩擦行为。可以用拉曼光谱分析HDLC的各种结构方面;但是分析HDLC表面上的磨损痕迹不能提供关于剪切平面结构的有洞察力的信息，因为拉曼的探针深度不够浅以区分来自本体膜的贡献。当不同的材料在HDLC上摩擦时，转移膜总是在相对表面上形成。由于转移膜是摩擦剪切的直接产物，因此可以假定分析转移膜可以描述摩擦过程中剪切面的特征，而不需要体积贡献的卷积。该研究采用显微拉曼分析来捕获由具有不同内源性H-含量（30和40 at. %）。该分析提供了统计学上有意义的数据，显示了在磨合和稳态摩擦期间剪切平面的石墨化和氢化程度如何随HDLC结构以及环境条件而变化，这是理解当HDLC用作固体润滑剂膜时如何诱导和改变超润滑性所急需的信息。
Hydrogenated diamond-like carbon (HDLC) has drawn significant interest as a solid lubricant coating due to its superlubricity. However, HDLC exhibits drastically different frictional behavior depending on hydrogen (H) content or sp2/sp3 carbon ratio. Various structural aspects of HDLC can be analyzed with Raman spectroscopy; but analyzing the wear track on the HDLC surface could not provide insightful information about the shear plane structure because the probe depth of Raman is not shallow enough to discriminate the contribution from the bulk film. When a dissimilar material is rubbed on HDLC, the transfer film is always formed on the counter-surface. Since the transfer film is the direct outcome of frictional shear, one can assume that analyzing the transfer film can depict characteristic features of the shear plane during friction without convolution from the bulk contri-bution. This study employed microscopic Raman analysis to capture hyperspectral images of the entire transfer films on a stainless-steel counter surface formed from HDLCs with different endogenous H-contents (30 and 40 at. % in the film) in gas environments of N2 and H2 (exogenous supply). This analysis provided statistically meaningful data showing how the degrees of graphitization and hydrogenation of the shear plane during the run-in and steady-state friction periods vary with the HDLC structure as well as the environment condition, which is critically needed information to understand how the superlubricity is induced and altered when HDLC is used as a solid lubricant film.