液态金属催化石墨烯纳米墙生长机理及其在CFRP装配制孔中的磨损机制研究

For diamond coated drills used in CFRP drilling, the attempt to elongate its lifetime, which is achieved by increasing the thickness of diamond coating, is largely limited to the necessary of maintaining the sharpness of tool cutting edge, which, in contrast, requires the thickness of diamond coating as thin as possible. Besides, the friction reducing effect of the diamond coating still requires to be further improved in order to meet the requirement of CFRP/Metal stack drilling. To solve these technical problems, we propose a novel idea in this project that aims to fabricate graphene nanowalls on the surface of diamond coated drills using liquid metal catalyst. The fabricated graphene nanowalls have 3-dimensional structure and are bonded to the diamond coating with C-C covalent bonds. They are able to significantly enhance the wear resistance and reduce the friction of the diamond coated drills, without causing cutting edge blunting, and thus are capable of elongating the tool lifetime, reducing the drilling cost and increasing the quality and efficiency of CFRP drilling. In this project, we will illustrate the physical mechanism of growing graphene nanowalls on the surface of diamond coating, explore the synergistic friction-reducing and anti-wear effect of graphene nanowalls with the diamond coating, develop the method of fabricating large-scale and high-quality graphene nanowalls on complex-shaped diamond coated drills, and reveal the wear mechanism of graphene nanowalls in CFRP and CFRP/Metal stack drilling. The study in this project will provide a novel coating solution for developing CFRP drilling tools and the cutting performance of the developed graphene/diamond coated drills in this project is expected to meet the requirements by the development of large passenger aircraft in China.

金刚石涂层刀具用于大型客机CFRP装配制孔时存在刀具延寿与加工质量提升的技术途径相互制约，以及涂层表面减摩特性无法满足CFRP/金属叠层制孔需求的技术瓶颈，难以满足我国大型客机研制需求。针对这一现状，本项目提出采用液态金属催化法在金刚石涂层刀具表面制备具有三维结构且与基底之间以碳-碳共价键结合的石墨烯纳米墙，显著提升刀具表面耐磨减摩特性，并有效避免刀具刃口钝化。拟从液态金属催化石墨烯纳米墙在金刚石涂层表面的生长机理、石墨烯纳米墙与金刚石涂层的协同耐磨减摩效应及其摩擦学机理、复杂形状金刚石涂层刀具表面大面积高质量石墨烯纳米墙制备方法以及石墨烯纳米墙在CFRP装配制孔中的磨损机制四个方面开展研究，达到延长刀具服役寿命，降低制孔成本，提高制孔质量与加工效率等目的。研究成果可为高性能CFRP制孔刀具的开发提供创新涂层解决方案，满足我国大型客机研制对CFRP高质高效制孔刀具的迫切需求。

针对切削刀具表面金刚石涂层服役寿命延长与加工质量提升的技术途径相互制约以及涂层表面耐磨性难以满足CFRP等高强度材料加工需求的技术难题，本项目采用液态金属催化CVD法成功在金刚石涂层表面制备了一层具有三维结构且与基底之间以碳-碳共价键结合的石墨烯纳米墙；对制备获得的石墨烯纳米墙的结构与质量进行了系统表征，并进一步通过研究反应工艺参数的影响规律，实现了石墨烯纳米墙结构的可控制备，提示了石墨烯纳米墙生长过程中液态金属Ga的催化作用以及碳原子的传质路径，阐明了其生长机理。研究了金刚石表面的石墨烯片层在不同工况下的摩擦学性能，揭示了石墨烯纳米墙对金刚石表面的耐磨减摩效应；进一步通过原子力显微镜与分子动力学仿真研究了微观尺度下石墨烯与金刚石在摩擦过程中的相互作用，揭示了石墨烯表面层的协同耐磨减摩效应的行为机理及失效机制。针对具有复杂几何形状的切削刀具表面，开发了基体表面预处理工艺与配套夹具，解决了液态金属作为催化剂存在的催化性能与浸润性相矛盾的技术难题，实现了液态金属催化剂与复杂形状基体表面的高质量共性接触问题；针对可转位切削刀片开发了专用沉积装备，可在刀具的前后刀具与切削刃表面制备获得均匀一致的高质量石墨烯纳米墙结构。在切削刀具表面制备了石墨烯/金刚石复合涂层，揭示了石墨烯涂层对降低金刚石涂层刀具的切削力、提高切削过程稳定性和加工表面质量以及降低最小切削厚度均有显著的效果；进一步针对具有复杂几何形状的切削刀具开发了石墨烯-金刚石共价异质结构涂层制备装置，并在MCD涂层刀具表面制备了均匀的石墨烯纳米墙。切削实验结果显示，石墨烯纳米墙可将金刚石涂层刀具的切削力进一步降低20%，刀具后刀面磨损速率降低20%以上。以上研究成果初步证明了石墨烯-金刚石复合涂层作为刀具表面涂层应用的可行性，为提高金刚石刀具切削性能提供了新的技术路径。