具有微纳米表面结构材料的微摩擦力学行为研究

Friction and wear plays an important role in influencing the work efficiency in micro-engineering region, especially for application of the cases of microelectro-mechanical systems (MEMS). Thus, studying friction problems at material surface and interface are nearly inevitable in engineering and technological applications. The tribological properties of the system are highly affected by the local plastic deformation pattern near the tip during the friction process, which is characterized by generation and evolution of basic microstructures such as dislocations, stacking faults and amorphous defects. This project focuses on investigating intrinsic relationship between microstructure characteristics and surface plastic behaviors during friction, which leads to the mechanism of friction at micro and nano scale. The content of our research includes: Research on size effect of dislocation nucleation at the subsurface during friction and its effect on friction process (such as static-dynamic friction transition). Study dislocation pile up at the interface or grain boundary during the scratch process, how does the back stress induced by the pile up affect the friction and wear. Research on surface morphology and defect effects on the nano and micro scale plastic behavior during contact and friction (dislocation nucleation, propagation, material distortion, surface rehealing etc).The aim of the project is to investigate the mechanism of nano and micro friction by comprehensively understanding the surface and interface plastic behavior during small scale contact and friction. The material microstructure effects on the tribological properties are studied at different scales, and the results from this study can be used as theoretical foundation for new surface-interface design, nano and micro surface engineering and friction optimization at different scales.

研究材料表面及界面的摩擦力学行为无论是对材料性能的改进优化还是对纳微电子机械系统的设计和应用，均具有迫切而重要的需求。材料表面及界面的摩擦力学特性直接与其受摩擦过程中的塑性行为相关，而摩擦引起的材料表面附近的塑性变形又直接与材料表界面微结构的形成及其演化特性相关。本项目试图通过研究摩擦过程中材料表界面微结构的形成和演化特征及摩擦表界面的塑性行为，获得对材料表界面摩擦力学机理的进一步表征。主要研究内容及目标为：研究接触过程中位错形核的尺度效应及其对摩擦力学性能的影响；研究材料界面上位错塞积及其与界面的相互作用对摩擦磨损力学行为的影响；研究接触摩擦条件下表界面的形貌和缺陷对微观塑性行为（包括位错发射及其演化，材料堆积，表面自修复等）的影响等。期望通过对材料表界面微观塑性机理的研究，为深入揭示微纳米摩擦力学性能机理、为新材料的表界面设计、为微纳米材料的表面工程和摩擦工程应用和技术等提供理论基础。

新材料系统的不断涌现，这对材料制备和加工过程中摩擦问题的关注度逐渐加大。而材料界面的摩擦力学性能与其受摩擦过程中的亚表面的塑性行为关系密切。因此，充分理解材料表面塑性行为的机制，对探索新材料表面摩擦行为的机理有着重要的实际意义。项目通过研究摩擦过程中材料表界面几种类型微结构形成和演化特征，揭示了表面塑性行为对材料表界面摩擦性能的影响，建立了微观摩擦界面物理模型，试图为新材料界面体系的设计提供帮助。主要的结论有：1）发展了格林函数分子力学方法，有效的减少了接触摩擦的分子力学研究的计算量，为后续大规模计算打下了基础。2）在纳米尺度，摩擦过程中产生的原子堆积起到了主要的作用，原子堆积不仅仅影响局部的应力分布，而且还影响位错的相互干涉；3）固体薄膜能够改善摩擦系统的性能，主要原理是界面对于位错以及层错的吸收和相互作用；4）界面微尺度的摩擦滑动的扩展速度和局部的应力状态相关。