离子注入辅助超精密加工基础研究

Hard and brittle crystals are widely utilized in many areas due to their physical and chemical properties. Although an optical surface could be achieved using ultra-precision machining, the machining results would ultimately suffer from the hard and brittle nature of those materials. To solve the problems mentioned above, a new ultra-precision machining method, which is assisted by surface modification through ion implantation, has been proposed by our team.Lattice damages or amorphization is previously introduced by an ion beam to reduce the hardness and elastic modulus of the surface layer. As a result, the tool life is prolonged with the guarantee of ductile region machining. The validity of this method has been proofed preliminarily on silicon, germanium, etc. This project will address a further study on the mechanism of this method. Based on the study of nanometric cutting, ductile brittle transition and ion implantation, the factors about brittleness in different scales and their connections can be explored. Then, new modification mechanisms and process for ultra-precision turning are proposed. The effect of this method on the refractive index will be investigated and manufacturing an antireflective microstructure array on single crystal silicon accroding to this method will be conducted. The theory of modification mechanism and process optimization would be implemented, which will lay a foundation for mass production of this method.

硬脆晶体由于具有良好的物化属性被广泛应用于军事及民用各个领域，相关加工技术的发展直接影响国家安全与国际竞争力。采用超精密加工方法虽然能够获得光学级表面，但最终会受到材料本身硬脆性质的制约。针对上述难题，本项目组提出了离子注入表面改性辅助超精密加工新方法，利用离子束流预先改变表面单晶结构，引入晶格损伤或非晶化，从而降低表层硬度、弹性模量，在保证塑性域加工前提下延长刀具使用寿命。该方法的有效性已在单晶硅、单晶锗等材料上得到初步验证。本项目将进一步针对该方法的作用机制展开深入研究，通过对纳米切削、脆塑转变、离子注入等过程的讨论，探索在不同尺度下影响材料脆塑性能的因素及其相互关系；进而提出新的改性机制以及针对超精密车削的新的加工方案；研究该方法对折射率的影响，并针对单晶硅减反射微结构阵列进行实际加工，最终实现完整的改性理论体系及基于实际需求的工艺参数设计方案，为该方法的产业化奠定基础。

晶体材料广泛应用于光学、微电子等高技术领域，由于其普遍具有硬脆属性，机械加工中很容易发生脆性断裂，破坏表面质量，并造成严重的刀具磨损。加工前若采用高能离子束轰击晶体表面，则可以降低材料表层机械强度、抑制表面脆性断裂。本项目针对离子注入表面改性辅助超精密加工方法中的基础问题展开深入研究，主要内容包括脆性材料纳米尺度切削机理，离子注入对材料纳米机械加工性能的影响机制，以及离子注入辅助加工方法的关键工艺。通过分子模拟与微纳加工技术，揭示了脆性晶体材料纳米尺度机械加工中的去除过程，进一步明确了剪切与推挤两种材料去除方式的基本过程与差异。获得表面离子改性层的微观结构（缺陷分布、改性层构型等）以及加工参数（刀具锋利度、切削速度等）对材料的纳米切削与断裂性能的影响规律。提出基于电离能损及裂纹隔离的表面改性与缺陷控制方法，验证其可行性，探索离子注入对红外材料表面反射率的影响，以及注入元素与材料力学性能的关系。优化离子注入改性方法工艺过程，提出多次注入策略以降低大厚度表面改性层的制备成本，显著提升单晶硅表面脆塑转变深度与纳米切削性能，实现大面积微结构阵列的塑性域加工。项目研究成果对脆性材料超精密机械加工及纳米切削基础理论体系的完善具有重要意义。