铜表面纳尺度沟槽织构的摩擦学性能

目的 通过分子动力学（MD）模拟，揭示了纳尺度沟槽织构对单晶铜摩擦磨损的影响机理，为设计高耐磨超声电机（USM）定子材料提供理论指导方法 建立了金刚石-铜摩擦配副模型，首先研究了金刚石下压深度对铜基体摩擦学性能的影响，随后重点研究了铜表面沟槽织构的角度、深度、宽度对摩擦学性能的影响。通过提取摩擦过程中的摩擦因数、磨损原子数目、摩擦界面温度、体系能量、界面间相互作用力以及观察摩擦前后界面形貌变化，从原子尺度揭示沟槽织构对铜的减摩机理。结果 对于无织构铜表面，摩擦因数和磨损率等性能参数随着下压深度的增加而增加；有沟槽织构的铜表面，摩擦因数和磨损率相较于无沟槽织构有显著下降。在沟槽织构与摩擦方向成90°时，效果最佳，摩擦因数下降25%左右，磨损率下降50%。同时，摩擦因数和磨损率还随沟槽深度和宽度的增大而减小。其主要原因是：沟槽织构的引入，使得在金刚石和铜基体的摩擦过程中相互作用的原子数量明显减少，相互犁削和接触原子的数量也减少，从而导致摩擦因数、磨损率下降。结论 在铜表面进行沟槽织构化处理能够减少摩擦过程中的磨损，提高铜基体的耐磨性能。

Effect of Groove on the Tribological Properties of Copper from a Nanoscale

Nanotribological properties of smooth and grooved copper surface during sliding processes were investigated by molecular dynamics (MD) simulation to understand the friction and wear mechanisms of copper stator for ultrasonic motor (USM) from an atomic dimension. In this study, A diamond-copper friction coupling model was established and embedded- atom (EAM) potential was adopted as a force field describing intermolecular forces. Firstly, the influence of diamond penetration depth on friction and wear of copper matrix was studied. Importantly, the influence of groove angle, depth, and width on the nanotribological property of the diamond-copper system was studied. Meanwhile, the friction reduction mechanism of the groove texture on copper was revealed by extracting and analyzing the friction coefficient, the interaction force between the atoms, interface temperature, the energy of system and the friction morphology during the friction process from nano scale. For the without-texture copper surface, the friction coefficient and wear rate increase with the increase of diamond penetration depth. According to the friction morphology, the wear becomes more serious with the increase of the penetration depth. The friction coefficient increased from 0.3 to about 0.57 and the number of worn atoms also showed a trend of rapid increase in the same groove depth and width. The interface temperature increased from nearly 317 K to 328 K. The main reason for the decrease of friction coefficient and wear rate was that the atoms squeezed and ploughed into each other were significantly reduced during the process of diamond and copper matrix friction interaction owing to the existence of groove texture. 90° grooved texture had the optimal effect on reducing friction and wear compared with other angles. The number of worn atoms at other angles was almost the same, and the 90° grooved texture had a significant decrease compared to them. Newtonian layers of 90° grooved texture were lower than those with other angles, and there was no significant difference in temperature variation between textures with other angles. Besides, the coefficient of friction and wear rate decreased with an increase of the groove depth. As the groove depth increased, the wear condition gradually eased according to the friction morphology in the same groove angle and width. In the process of increasing the groove depth from 0nm to 0.8 nm, the number of worn atoms was reduced by nearly 78%, friction coefficient dropped from 0.57 to 0.46. In addition, van der Waals force decreased from about 35 nN to 20 nN, decreasing by 42.8%. In this case, the interface temperature dropped from 327 K to 318 K. The change of groove width was similar to the trend of groove depth. Therefore, the grooved surface can help improve the nanotribological performance and alleviate the wear on the copper surface. Increasing the penetration depth not only can increase the friction, but also produce severe wear in the form of material pile-up. Grooved angle has a great influence on friction and wear caused by the distribution of copper atoms. This study will provide theoretical guidance for exploring the wear mechanism of the textured copper surface from a nanoscale.