基于亲和作用机理的金刚石低温摩擦磨损研究

Friction-induced affinity effect between the diamond and the metals, such as iron and titanium, can be inhibited by cryogenic temperature, which makes a tiny material loss of diamond. Taken advantage of this, the demand of ultra-precision diamond cutting of pure iron (used for material radiative ablation and precision physical experiments under extreme conditions) and pure titanium (used for micro-electromechanical systems manufacture and biomedical metallic materials) will be satisfied, and a new lapping technique of ultra-smooth and low damage diamond surface (used for fabricating high quality chemical vapor deposition diamond for the quantum information and other technologies) can be developed. However, it hasn’t yet been paid enough attention to. The key of its application and development is to understand the law of diamond cryogenic friction and wear caused by affinity effect. With our accumulation of theory and technology of diamond and its tool lapping, the research group will study the smooth surface generation, surface damage layer and wear behavior of diamond under cryogenic condition based on the affinity effect, by means of observation approaches , such as AFM (atomic force microscope) and STM (transmission electron microscope), and theory analysis methods, such as MD (molecular dynamics) simulation. Our research gives the basic theory and technology support for the realization of ultra-precision diamond cutting of pure iron and titanium and the new lapping technique of near ideal diamond surface.

低温可抑制金刚石与铁、钛等金属间由摩擦引起的亲和作用，使金刚石损耗极小。利用该现象可满足纯铁（可用于材料辐射烧蚀和极端条件精密物理实验）和纯钛（可用于微电子制造和医用金属材料）对超精密金刚石切削加工的需求以及开发超光滑低损伤金刚石表面（可用于量子信息等技术需求的高质量化学气相沉积金刚石制备）研磨新工艺，然而，长久以来并未引起重视。认识基于亲和作用机理的金刚石低温摩擦磨损规律，对其应用开发尤为关键。项目组在金刚石及其工具研磨的理论技术积累上，借助原子力显微镜、透射电子显微镜等观测手段和分子动力学等理论分析方法，对金刚石在低温条件下基于亲和作用机理的光滑表面的创成、表面损伤层和磨损行为展开研究，揭示内在材料迁移行为，掌握摩擦因素的影响规律。本研究对于实现纯铁纯钛的超精密金刚石切削和接近理想金刚石表面的研磨新工艺提供基础理论和技术支撑。

金刚石以其优异的理化性能在工业技术领域具有关键甚至无可替代的应用需求，特别是在光学窗口、有望替代硅的新一代半导体、X射线光学透镜、超精密机械加工用刀具等领域。低温可抑制金刚石与铁、钛等金属间的亲和作用，金刚石损耗极小。利用该现象可开发超光滑低损伤金刚石表面的研磨新工艺。本项目首先通过设计搭建的液氮低温冷却研磨盘实现了金刚石在约-170℃低温下的研抛工艺。继而，项目组在金刚石及其工具研磨的理论技术积累上，借助原子力显微镜、透射电子显微镜和X射线光电子能谱等观测手段和分子动力学理论仿真方法，对金刚石在低温条件下基于亲和作用机理的光滑表面创成、表面损伤层和磨损行为展开研究。研究中发现钛与金刚石在常温和低温下摩擦均会粘结在金刚石表面，不能对金刚石实现有效的材料去除。进一步研究铁研抛金刚石表明：影响光滑金刚石表面形成的主要原因是抛光中工件和抛光盘表面单次接触极小的材料去除量，若能进一步提高抛光中工件/工具接触面之间接触的均匀性可进一步提高金刚石表面光滑程度；沿着难磨晶向在低温下对金刚石表面研抛，易产生破损现象，压力和速度在一定的范围内对金刚石表层组织的影响不明显；纯铁与金刚石之间的摩擦，金刚石材料的去除以碳原子向铁中扩散为主，金刚石的晶体层与非晶层之间的分界较为明显，非晶层的厚度集中在2.3nm左右，且厚度不均一，厚的地方在10nm左右，远小于机械研磨的表面损伤层厚度；金刚石的表层含有C、O元素，以sp2型C原子为主，无Fe元素，低温抛光的金刚石表面还含有N元素；低温抑制了碳原子的空穴扩散和间隙扩散，金刚石磨损率在低温下受到了明显的抑制，约是常温条件下的1/10。通过本项目获得了金刚石液氮低温抛光工艺整套技术，认识了金刚石材料的去除行为和亚表层损伤，获得了金刚石去除率和损伤层深度数据，为后续金刚石工件加工的尺寸控制和超光滑表面获得提供了技术基础。