“壳簧”结构GN-MLD复合薄膜的减摩耐磨机理研究

Graphene (GN) based coating can play a lubricating and protective role in micro-mechanical systems. The structural characteristics plays key important role in antifriction and wear resistance of the coating. Molecular layer deposition (MLD) technique is used to prepare ordered molecular adhesive layer between substrate and GN. The flexibility of MLD layer and the binding state between GN and MLD layers are to be adjusted, in order to build a GN-MLD composite coating system with shell-spring structure. Nano-indentation and atomic force microscopy (AFM) are to be used to complement loading-unloading tests, which can determine the micro-hardness, elastic modulus and critical load of plastic deformation for the coating, the influence of interface bonding state and thickness of the adhesive layer on the load-carrying capacity of the composite coating is to be revealed. By characterizing the physical and chemical features of the coating surface, and testing the frictional properties of AFM, the inhibition effect of surface/interface characteristics on the out-of-plane flexibility of the GN layer is to be analyzed, and the frictional behavior and mechanism for the GN layer under strong substrate-adhesion condition are to be revealed. The anti-wear properties of the coating, such as shear yield strength and critical wear load, are to be characterized by nano-wear and scratch test methods of AFM, the relationship model of GN layer characteristics and flexibility of MLD layer on reducing shear and enhancing load-bearing capacity of GN-MLD composite film is to be established, and the wear resistance mechanism of structural characteristics on GN-MLD composite coating is aimed to be revealed. The accomplishment of this study can provide theoretical basis for optimum design and friction behavior control of GN-based lubrication coatings.

石墨烯（GN）基固体润滑薄膜在微机械系统中起减摩耐磨作用。薄膜结构是影响其减摩耐磨性能的关键因素。项目采用分子层沉积（MLD）技术制备基底与GN间的有序分子粘附层，调控MLD层柔性及界面间结合状态，构筑具有“壳-簧”结构的GN-MLD复合薄膜体系。采用纳米压痕和原子力显微镜（AFM）的加-卸载试验表征薄膜微观硬度、弹性模量及抗压临界载荷等力学性能，揭示薄膜界面结合状态、粘附层厚度对其承载能力的影响规律；利用薄膜表面理化性能和AFM摩擦性能测试，探明表/界面特性对GN层面外柔性的抑制作用关系，揭示强黏着条件下GN层摩擦行为机理；采用AFM纳米磨损及划痕试验方法，建立薄膜剪切屈服强度、磨损临界载荷等抗磨性能指标，阐明GN层特性、MLD层柔性对薄膜降剪切、增强承载能力的作用机制，揭示结构特性对GN-MLD复合薄膜的耐磨作用机理。为GN基润滑薄膜的优化设计及摩擦行为调控提供理论基础。

基于纳米机械系统中无油、极小间隙的固体润滑特殊需求，开展了石墨烯-分子层沉积（MLD）复合薄膜的制备及摩擦磨损性能研究。项目开创薄膜几何结构角度研究了复合薄膜的减摩耐磨机理，通过调控不同几何结构特性的薄膜，分析几何结构对复合薄膜摩擦学性能的影响规律，揭示复合薄膜减摩耐磨机理，丰富纳米摩擦学理论。.主要研究内容及重要结论如下。①研发了一种用于制备层状有机分子MLD表面膜的设备，应用于本项目中制备有机分子的MLD薄膜，即“簧”结构。②研究MLD薄膜制备工艺参数调控对薄膜成膜质量的影响规律，获得了MLD复合薄膜的最佳制备工艺，成功采用MLD方法制备工艺稳定的“簧”结构MLD薄膜；采用水溶液自组装方法在MLD薄膜表面沉积氧化石墨烯层（“壳”），获得“石墨烯+MLD薄膜”的“壳簧”结构薄膜。③对各类薄膜进行纳米力学试验，获得其弹性模量、微观硬度，发现随着中间MLD薄膜厚度增加壳簧结构薄膜由弹性薄膜转变为弹塑性薄膜。④采用分子动力学方法建立六种薄膜，实现不同MLD层厚度、不同石墨烯-MLD界面结合方式、不同石墨烯层化学活性的调控。⑤采用分子动力学方法模拟压痕和摩擦行为，揭示薄膜减摩耐磨机：石墨烯增加薄膜的承压面积及抗撕裂能力因此增强薄膜承压能力；MLD层的厚度与薄膜柔性不是递增关系，薄膜刚度随MLD厚度的增加先提高后降低；石墨烯层表面功能团的去除对承压能力影响不大，但能够有效降低薄膜摩擦系数；MLD膜厚度的增加降低薄膜结构稳定性，在长期摩擦工况下薄膜破坏发生在中间MLD膜部分；物理吸附的石墨烯层具有更高的静态抗压能力和摩擦系数，但易被剪切剥离产生磨屑，不利于对洁净度要求较高场合；摩擦过程中石墨烯“壳”将孤立的分子链链接形成整体抗磨结构，相比于无石墨烯层的MLD薄膜，更多的MLD分子链参与抵抗摩擦剪切，扩大了薄膜承压面积，因此提高薄膜耐磨性；发现石墨烯-MLD复合薄膜因探针滑过而产生的“摇摆行为”，并用于解释薄膜在摩擦过程中摩擦系数类周期性波动产生的原因。