Structural and environmental dependence of superlow friction in ion vapour-deposited a-C : H : Si films for solid lubrication application
Structural and environmental dependence of superlow friction in ion vapour-deposited a-C : H : Si films for solid lubrication application
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DOI：
10.1088/0022-3727/46/25/255304
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发表时间：
2013-06
期刊：
影响因子：
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通讯作者：
Xinchun Chen;Takahisa Kato;M. Kawaguchi;M. Nosaka;Junho Choi
中科院分区：
文献类型：
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作者：
Xinchun Chen;Takahisa Kato;M. Kawaguchi;M. Nosaka;Junho Choi
了解潮湿环境中水分子与碳膜表面，特别是亲水表面的摩擦化学相互作用，是摩擦学和固体润滑应用的基础。本文重点介绍了一些实验证据，以阐明超低甚至超低摩擦的离子气相沉积a-C：H：Si薄膜的结构和环境的依赖性。结果表明，硅羟基（Si-OH）表面密度和相对湿度（RH）共同决定了a-C：H：Si薄膜的摩擦性能。超低摩擦系数μ（≤ 0.01-0.055）在较宽的相对湿度范围内是可行的。亲水性Si-OH表面的解离形成和随之而来的界面水分子在接触压力下的纳米结构是a-C：H：Si薄膜在潮湿环境中超低摩擦的来源。根据赫兹接触模型推导出的接触压力与摩擦系数之间的关系式在本文中是不成立的。在这种纳米级边界润滑下，摩擦系数趋于随着接触压力的增加而增加。甚至存在从超低摩擦过渡到超低摩擦的接触压力阈值（μ C 0.007）。相比之下，当在干燥N2中进行摩擦测试时，在不存在水的情况下观察到的超低摩擦（μ C 0.004）与通过磨损诱导的相变形成的低剪切强度摩擦层相关。
Understanding the tribochemical interaction of water molecules in humid environment with carbonaceous film surfaces, especially hydrophilic surface, is fundamental for applications in tribology and solid lubrication. This paper highlights some experimental evidence to elucidate the structural and environmental dependence of ultralow or even superlow friction in ion vapour-deposited a-C : H : Si films. The results indicate that both surface density of silicon hydroxyl group (Si–OH) and humidity level (RH) determine the frictional performance of a-C : H : Si films. Ultralow friction coefficient μ (∼0.01–0.055) is feasible in a wide range of RH. The dissociative formation of hydrophilic Si–OH surface and the following nanostructure of interfacial water molecules under contact pressure are the origin of ultralow friction for a-C : H : Si films in humid environment. The correlation between contact pressure and friction coefficient derived from Hertzian contact model is not valid in the present case. Under this nanoscale boundary lubrication, the friction coefficient tends to increase as the contact pressure increases. There even exists a contact pressure threshold for the transition from ultralow to superlow friction (μ ∼ 0.007). In comparison, when tribotested in dry N2, the observed superlow friction (μ ∼ 0.004) in the absence of water is correlated with the formation of a low shear strength tribolayer by wear-induced phase transformation.