Wang Kang, Zhang Jie, Ma Tianbao, Liu Yanmin, Song Aisheng, Chen Xinchun, Hu Yuanzhong, Carpick Robert W, Luo Jianbin
State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China.
Beijing Institute of Control Engineering, Beijing, 100094, China.
Small. 2021 Jan;17(1):e2005607. doi: 10.1002/smll.202005607. Epub 2020 Dec 7.
Diamond-like carbon (DLC) films are capable of achieving superlubricity at sliding interfaces by a rapid running-in process. However, fundamental mechanisms governing the friction evolution during this running-in processes remain elusive especially at the nanoscale, which hinders strategic tailoring of tribosystems for minimizing friction and wear. Here, it is revealed that the running-in governing superlubricity of DLC demonstrates two sub-stages in single-asperity nanocontacts. The first stage, mechanical removal of a thin oxide layer, is described quantitatively by a stress-activated Arrhenius model. In the second stage, a large friction decrease occurs due to a structural ordering transformation, with the kinetics well described by the Johnson-Mehl-Avrami-Kolmogorov model with a modified load dependence of the activation energy. The direct observation of a graphitic-layered transfer film formation together with the measured Avrami exponent reveal the primary mechanism of the ordering transformation. The findings provide fundamental insights into friction evolution mechanisms, and design criteria for superlubricity.
类金刚石碳（DLC）薄膜能够通过快速磨合过程在滑动界面实现超润滑。然而，在这个磨合过程中控制摩擦演变的基本机制仍然不清楚，尤其是在纳米尺度上，这阻碍了摩擦系统的战略定制以最小化摩擦和磨损。在此，揭示了DLC超润滑磨合在单峰纳米接触中表现出两个子阶段。第一阶段，薄氧化层的机械去除，由应力激活的阿累尼乌斯模型定量描述。在第二阶段，由于结构有序转变，摩擦力大幅下降，其动力学由修正了活化能负载依赖性的约翰逊-梅耳-阿弗拉米-柯尔莫哥洛夫模型很好地描述。对石墨层状转移膜形成的直接观察以及测量的阿弗拉米指数揭示了有序转变的主要机制。这些发现为摩擦演变机制和超润滑设计标准提供了基本见解。
