类金刚石纳米磨损的能量耗散机理研究

Miniaturization of machines and their components is the new trend of mechanical technology development. Many small-scale machines and components have been developed, such as drug-delivery robot, nanoscale bearing and gears. As a result, investigation of tribology at the small-scale, particularly at the nanoscale, is significant to ensure their normal working and long lifetime. However, the limitations of experimental approaches lead to the unclear wear mechanisms at the nanoscale. This project is proposed to use molecular dynamics simulation to investigate the nanowear mechanisms of diamond-like carbon (DLC) films via energy dissipation analysis. The different factors such as velocities, loads, environment temperatures, film compositions and surface modifiers will be considered. Analysis will be conducted on the influence of interfacial adhesion strength, contact area, contact stress and shear stress on the wear behaviors of DLC films, which will help to examine the applicability of Eyring-type and Archard-type wear equation at the nanoscale. Such information will be collected to plot the wear map of DLC films. The nanowear mechanisms of DLC films will also be discussed by analyzing the influence of their graphitization, friction temperature, and diffusion of surface modifier atoms on their mechanical and tribology behaviors. Energy dissipations by different modes including deformations, graphitization, heat diffusions, atom diffusions and wear will be calculated, leading to the correlation between wear volume and friction forces. The results will help to improve the understanding of nanowear mechanisms and promote the wide applications of DLC films at the nanoscale.

机械小尺度化是21世纪机械装备发展的主要趋势之一，如MEMS/NEMS、载药机器人、纳米轴承和齿轮等微小机械的开发极大促进机电、医疗等领域的科技进步。深入理解小尺度下材料摩擦磨损行为，成为保障小尺度机械正常运行的基本前提。由于实验手段的限制，小尺度（尤其纳米尺度）材料的磨损机理至今仍缺少清晰的认识。本项目以分子动力学为手段，研究类金刚石的纳米磨损行为，分析其能量耗散机制，建立纳米磨损与测试条件、材料特性及摩擦力的关联性。项目拟系统地考察诸多因素（包括速度、载荷、温度、成分以及表面修饰等）对纳米磨损行为的影响，论证Arrhenius和Archard磨损模式在纳米尺度的适用性，绘制类金刚石的纳米磨损相图，分析多种能量耗散方式（石墨化相变、热耗散、变形以及原子扩散等）对类金刚石纳米磨损性能的影响。研究结果将有助于促进纳米磨损学科的发展，并为类金刚石在小尺度的应用提供理论支撑。

机械小尺度化是21世纪机械装备发展的主要趋势之一，如MEMS/NEMS、载药机器人、纳米轴承和齿轮等微小机械的开发极大促进机电、医疗等领域的科技进步。深入理解小尺度下材料摩擦磨损行为，成为保障小尺度机械正常运行的基本前提。由于实验手段的限制，小尺度（尤其纳米尺度）材料的磨损机理至今仍缺少清晰的认识。本项目以分子动力学为手段，研究了不同测试条件下类金刚石的纳米摩擦磨损行为，分析了不同条件下类金刚石的纳米摩擦磨损机理，并基于能量耗散分析建立了纳米磨损与测试条件、材料性质及摩擦力的直接联系。研究发现不同测试条件下类金刚石的磨损体积与其结构转变、摩擦界面温度、界面粘着力等因素密切相关，而润滑介质能够通过参与界面活动有效降低界面粘着力、进而影响温度与结构变化；类金刚石纳米摩擦界面显示出类流体的涡流特点，且摩擦界面处热导率呈现各向异性，说明了摩擦过程中能量耗散方式存在转变；针对摩擦过程中拉应力/压应力等不同条件，开展了类金刚石弹塑性变形机理分析，发现石墨化转化在应变集中区域发生，导致该区域在压应力作用下出现滑移，对应于类金刚石摩擦过程中的结构易剪切行为；最后通过能量耗散分析解析了摩擦过程中的多种能量耗散方式占比变化情况，提出的理论预测值与文献中实验测试数值趋近，验证了基于分子动力学与能量耗散分析手段预测磨损的可行性。研究结果将有助于提高对纳米磨损的理解，并为促进类金刚石在小尺度的工业应用提供理论支撑。