Chen Xinchun, Kato Takahisa, Nosaka Masataka
Department of Mechanical Engineering, The University of Tokyo , 113-8656 Tokyo, Japan.
ACS Appl Mater Interfaces. 2014 Aug 27;6(16):13389-405. doi: 10.1021/am502416w. Epub 2014 Aug 18.
Superlubricity of Si-containing hydrogenated amorphous carbon (a-C:H:Si) films has been systematically investigated in relation to the film bonding structure and the environmental atmosphere. Structural diversity induced by hydrogen incorporation (i.e., 17.3-36.7 at. % H), namely sp(2)-bonded a-C, diamond-like or polymer-like, and tribointeractions activated by the participation of environmental gaseous molecules mainly determine the frictional behaviors of a-C:H:Si films. A suitable control of hydrogen content in the film (i.e., the inherent hydrogen coverage) is obligate to obtain durable superlubricity in a distinct gaseous atmosphere such as dry N2, reactive H2 or humid air. Rapid buildup of running-in-induced antifriction tribolayers at the contact interface, which is more feasible in self-mated sliding, is crucial for achieving a superlubric state. Superior tribological performances have been observed for the polymer-like a-C:H:Si (31.9 at. % H) film, as this hydrogen-rich sample can exhibit superlow friction in various atmospheres including dry inert N2 (μ ∼ 0.001), Ar (μ ∼ 0.012), reactive H2 (μ ∼ 0.003) and humid air (μ ∼ 0.004), and can maintain ultralow friction in corrosive O2 (μ ∼ 0.084). Hydrogen is highlighted for its decisive role in obtaining superlow friction. The occurrence of superlubricity in a-C:H:Si films is generally attributed to a synergistic effect of phase transformation, surface passivation and shear localization, for instance, the near-frictionless state occurred in dry N2. The contribution of each mechanism to the friction reduction depends on the specific intrafilm and interfilm interactions along with the atmospheric effects. These antifriction a-C:H:Si films are promising for industrial applications as lubricants.
含硅氢化非晶碳（a-C:H:Si）薄膜的超润滑性已针对薄膜键合结构和环境气氛进行了系统研究。氢掺入（即17.3 - 36.7原子% H）引起的结构多样性，即sp(2)键合的非晶碳、类金刚石或类聚合物结构，以及环境气体分子参与激活的摩擦相互作用，主要决定了a-C:H:Si薄膜的摩擦行为。在诸如干燥N2、反应性H2或潮湿空气等特定气体气氛中获得持久的超润滑性，必须对薄膜中的氢含量（即固有氢覆盖率）进行适当控制。在接触界面快速形成磨合诱导的减摩摩擦层，这在自配对滑动中更可行，对于实现超润滑状态至关重要。已观察到类聚合物a-C:H:Si（31.9原子% H）薄膜具有优异的摩擦学性能，因为这种富氢样品在包括干燥惰性N2（μ ∼ 0.001）（μ ∼ 0.012）、反应性H2（μ ∼ 0.003）和潮湿空气（μ ∼ 0.004）在内的各种气氛中都能表现出超低摩擦，并且在腐蚀性O2（μ ∼ 0.084）中能保持超低摩擦。氢因其在获得超低摩擦方面的决定性作用而备受关注。a-C:H:Si薄膜中超润滑性的出现通常归因于相变、表面钝化和剪切局部化的协同作用，例如在干燥N2中出现的近无摩擦状态。每种机制对摩擦降低的贡献取决于特定的膜内和膜间相互作用以及大气效应。这些减摩a-C:H:Si薄膜作为润滑剂在工业应用中具有广阔前景。
