单晶硅磨抛协同加工的分子动力学

磨削与抛光是实现单晶硅材料超精密表面加工的重要工艺方法，磨抛协同加工过程中由磨粒运动状态主导的二体与三体磨损机制对材料去除效率以及表面加工质量具有重要影响。采用分子动力学方法，建立固结与游离运动状态双磨粒协同作用下的单晶硅表面超精密磨抛加工过程仿真模型，分析磨粒切入深度、横向与纵向间距干涉等因素对磨削力、材料相变、表面损伤及材料去除行为的影响规律，阐释单晶硅磨抛协同超精密加工表面形貌演化规律。研究表明：受磨粒运动状态驱动的单晶硅材料表层损伤原子数量随固结及游离磨粒切入深度增大而增加，磨粒切入深度对工件的材料去除、裂纹生长及损伤行为影响显著；法向和切向磨削力随磨粒切入深度增加而增大，且在同等切入深度变化时法向磨削力增加幅度大于切向磨削力； 通过单晶硅金刚石结构分析磨粒间干涉区域的损伤情况可知，随着磨粒间纵向间距增加时，工件所受干涉作用减小，六角金刚石晶体结构减少；相比较固结磨粒，游离磨粒对工件的损伤区域更深，产生瞬态缺陷原子更多。研究结果可为实现超精密磨抛协同加工工艺高材料去除效率和高表面质量提供理论基础。

Molecular Dynamics of the Grinding and Polishing Collaborative-processing on Monocrystalline Silicon

Monocrystalline silicon, a crystalline material widely employed in semiconductor chips, optical components, photovoltaic devices, and other high-end manufacturing applications, possesses exceptional attributes, such as high hardness, strength, thermal stability, and corrosion resistance. Nevertheless, the remarkable mechanical properties and chemical stability of monocrystalline silicon pose significant challenges in machining. Rigid contact between machining tools and materials frequently causes structural and surface quality defects, including cracks and pits, significantly impairing product performance. Currently, the primary method for achieving ultraprecision surface manufacturing of monocrystalline silicon materials is grinding and polishing. The dynamics of abrasive movements during these processes, governing the two-body and three-body wear mechanisms, have a profound impact on the material removal efficiency and surface finish quality. Despite their critical importance, there is a notable research gap in understanding the material-removal mechanisms and surface-morphology evolution during grinding and polishing. To address this gap, our study introduces a molecular dynamics simulation model for the ultraprecision grinding and polishing of single-crystal silicon surfaces, encompassing both fixed and loose abrasives. Our model scrutinizes several pivotal parameters: the depth of cut of the abrasives, the lateral and longitudinal spacing, and their respective effects on the grinding force, material phase transformation, temperature, surface damage, and material removal behavior. The aim was to unveil the underlying principles governing the evolution of surface morphology during the ultra-precision grinding and polishing of single-crystal silicon. Our findings indicate that an increase in the depth of cut for both fixed and loose abrasives results in a higher number of damaged surface atoms in single-crystal silicon materials. The depth of cut significantly influences material removal, crack propagation, and workpiece damage. Notably, both the normal and tangential grinding forces increased with the depth of cut, with the normal grinding force displaying a more pronounced increment for equivalent changes in the depth of cut. Conversely, the tangential force exhibited greater sensitivity to alterations in lateral and longitudinal spacing. However, the tangential grinding force decreased with increasing lateral spacing, followed by an initial decline and then an increase with increasing longitudinal spacing. Our study indicates that the temperature of the workpiece is primarily affected by the depth of cut of the abrasives, whereas the influence of the lateral and longitudinal spacing on the temperature is negligible. An analysis of the diamond structure of single-crystal silicon revealed that a greater longitudinal spacing between abrasives resulted in reduced interference on the workpiece, a decrease in the hexagonal diamond crystal structure, deeper workpiece damage caused by loose abrasives, and an increase in transient defect atoms. A deeper cut depth led to a broader damaged area on the workpiece, a more frequent appearance of the hexagonal diamond crystal structure, and an increased depth of the damaged layer. Regarding the surface morphology, an increasing depth of cut causes a substantial accumulation of atoms from both fixed and loose abrasives during grinding and polishing, resulting in enhanced material removal. A larger lateral spacing enables loose abrasives to polish a larger area, remove more atoms, and consequently increase the atom accumulation. The Wigner-Seitz defect analysis revealed that during the fixed and free abrasive grinding and polishing processes, the grain gap area on the surface of the interference region increased with an increase in lateral spacing. As the cutting depth increases, more atoms are removed from the interference region after grinding and polishing. In the cross-section of the interference region, material removal decreased with an increase in lateral spacing, whereas longitudinal spacing had no significant effect on material removal. However, increasing the cutting depth of the abrasives led to a notable increase in material removal, resulting in larger gap areas and smaller gap sizes, indicating more pronounced atom extrusion. Therefore, this study establishes a robust theoretical foundation for achieving high material removal efficiency and superior surface quality during ultraprecision grinding and polishing processes.