Reactive Molecular Dynamics Simulations of Wear and Tribochemical Reactions of Diamond like Carbon Interfaces with Nanoscale Asperities under H2 Gas: Implications for Solid Lubricant Coatings
Reactive Molecular Dynamics Simulations of Wear and Tribochemical Reactions of Diamond like Carbon Interfaces with Nanoscale Asperities under H2 Gas: Implications for Solid Lubricant Coatings
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DOI：
10.1021/acsanm.0c01775
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发表时间：
2020-07-24
影响因子：
5.9
通讯作者：
Kubo, Momoji
中科院分区：
文献类型：
--
作者：
Wang, Yang;Su, Yixin;Kubo, Momoji
类金刚石(DLC)是一种优良的固体润滑涂层，广泛应用于纳米机电系统和原子力显微镜等纳米尺度领域。减少DLC涂层的磨损是提高其耐久性和可靠性的关键。通常，由于DLC与环境气体发生摩擦化学反应，其磨损强烈依赖于工作环境；然而，由于DLC的磨损机理来自复杂的原子尺度磨损过程和摩擦化学反应，因此还没有建立通过控制环境来减少磨损的理论指南。在这里，我们成功地利用反应分子动力学模拟揭示了DLC在氢气环境中的磨损和摩擦化学反应之间的关系，为减磨提供了理论指导。在DLC摩擦界面，我们发现了两种不同类型的摩擦化学反应：一种是加速摩擦，另一种是减少磨损。加速磨损的反应是碳氢分子从类金刚石表面释放出来。碳氢化合物的排放逐渐耗尽了表面的氢末端，加速了表面的粘合，最终导致了严重的粘合诱导的机械磨损。相反，减少磨损的反应是氢分子从环境中解离吸附到DLC表面。氢气吸附补充了耗尽的氢端，抑制了表面附着，直接降低了类金刚石的机械磨损。失去和补充表面氢端的反应分别加速和抑制了DLC的磨损。这项工作将有助于通过控制摩擦化学反应来建立减磨指南。
Diamond like carbon (DLC) is an excellent solid lubricant coating used in various nanoscale applications such as nanoelectromechanical systems and atomic force microscopy. Reducing the wear of DLC coatings is essential for improving their durability and reliability. Generally, the wear of DLC is strongly dependent on the working environment because of the tribochemical reactions with environmental gases; however, theoretical guidelines for wear reduction by controlling environments have not been established yet because the wear mechanisms arise from complex atomic-scale wear processes and tribochemical reactions. Here, we successfully use reactive molecular dynamics simulations to reveal the relations between wear and tribochemical reactions of DLC in a hydrogen gas environment, contributing to the wear reduction as a theoretical guideline. At the DLC friction interface, we find two different types of tribochemical reaction: one accelerates, whereas another reduces the wear. The reaction that accelerates wear is the emission of hydrocarbon molecules from the DLC surface. Hydrocarbon emission gradually depletes surface hydrogen terminations, accelerating surface adhesion and finally leading to severe adhesion-induced mechanical wear. In contrast, the reaction that reduces wear is the dissociative adsorption of hydrogen molecules from the environment onto the DLC surface. Hydrogen gas adsorption replenishes the depleted hydrogen terminations and suppresses surface adhesion, which directly reduces the mechanical wear of DLC. The reactions of losing and replenishing surface hydrogen terminations accelerate and suppress the wear of DLC, respectively. This work would contribute to establishing a guideline for wear reduction by controlling the tribochemical reactions.