单晶铜衬底的磁场辅助超精密车削机理研究

Single crystal copper substrates are the critical foundation to prepare large single crystal graphene by CVD method. The biggest problem that faced in the industrial production of graphene film is the supply of single crystal copper substrate with the strict surface integrity requirements. The industrial production of graphene film has the urgent demand for ultra-precision turning of high quality single crystal copper substrate. However, there are polycrystalline defect problems in subsurface of single crystal copper substrate during ultra-precision cutting. This project investigates the transition mechanisms of single crystal structure to polycrystalline structure during ultra-precision cutting process to obtain the critical conditions for the generation of subgrain boundary and grain boundary, and then clarifies the formation mechanisms of subsurface defects. Then, the effect mechanisms of magnetic field to reduce the plastic deformation on machined surface and suppress the polycrystalline defects in subsurface during ultra-precision cutting will be investigated in detail. With the stable introduction method of magnetic felid, a magnetic field assisted ultra-precision turning technology is proposed to control the subsurface defects. The purpose of this project is to solve the polycrystalline defect problems in subsurface of single crystal copper substrate and further improve the surface integrity limit in ultra-precision turning.

单晶铜衬底是CVD法制备大面积单晶石墨烯的重要基石，具有极高表面完整性要求的单晶铜衬底也是石墨烯薄膜迈向产业化面临的最大问题，解决高品质单晶铜衬底的超精密车削加工难题是实现石墨烯薄膜产业化的迫切需求。本项目针对单晶铜衬底加工表面存在的亚表层多晶缺陷问题，通过研究超精密切削过程中单晶向多晶结构的演变机理，探明产生亚晶界或晶界等晶体缺陷的临界条件，阐明多晶层缺陷的形成机理；进而研究磁场效应对超精密切削过程中改善加工表面塑性变形和抑制亚表层多晶演变的作用机理，探索稳定的磁场引入方式，创造性地将超精密车削和磁场作用结合，提出亚表层缺陷可控的磁场辅助超精密车削技术，最终解决单晶铜衬底亚表层缺陷的工艺控制难题，进一步提高超精密车削加工表面完整性的极限。

本项目针对石墨烯制备用的单晶铜（111）晶面衬底，通过开展分子动力学仿真研究，探明了单晶铜加工表面的亚表层多晶缺陷形成机理，分析了切削深度、切削速度、切削方向等不同参数对亚表层缺陷的影响规律；搭建了磁场辅助单点金刚石车削平台，将磁场作用引入到切削过程中以进行磁场辅助单点金刚石车削实验，结果表明，与传统车削相比，由于磁致减摩和磁塑效应的影响，磁场辅助单点金刚石车削可以降低约16%的切削力比和前刀面摩擦系数，并减小金属切削过程中切屑变形程度，从而改善加工表面粗糙度。