Mechanisms of brittle-ductile transition and material removal in diamond cutting of silicon carbide

与其他加工方法相比，硬脆陶瓷的金刚石切割具有几个优点，例如磨削。然而，这也是一项技术挑战，因为它需要对材料去除机理的精确知识，以确保稳定的工艺和高质量的表面抛光。虽然大多数陶瓷在宏观测试中表现出完全脆性，但微观机械测试经常显示出材料的一些延展性。在金刚石切割过程中，可以观察到这种脆性-延性转变(BDT)，这取决于工艺参数。已有文献表明，在延展性区域操作金刚石切割过程是有利的，因为它导致加工零件的表面粗糙度超低。在拟议的研究项目中，将在所有相关的长度尺度上结合比例桥接材料和工艺建模以及现场和非现场实验来研究碳化硅陶瓷的金刚石切割过程。选择碳化硅作为材料是因为它在光学器件中的应用对表面质量要求极高。然而，这种陶瓷的高硬度和脆性给工艺带来了巨大的挑战，只有从根本上了解材料去除的机理才能掌握这一工艺。因此，本研究项目的第一个目标是研究金刚石切割条件下碳化硅中BDT的形成机理。此外，该项目将对精密加工过程中材料去除的机理有一个新的理解，包括脆性和延性区域，重点是延性材料的去除过程。作为该项目的第二个目标，所获得的理解和开发的比例桥接模型将用于支持在精密加工过程中实现表面粗糙度小于10 nm的工艺创新。如此高的加工精度只能通过对基本机理的非常详细的了解以及通过使用数值模型和关键实验来设计所需的刀具来实现。一个关键问题将是控制精密加工过程，以便只去除延性材料，因为这将产生更好的表面质量。因此，项目的基础部分是建立这种过程创新的必然要求。虽然这个项目的本质是为碳化硅系统描述相当具体的材料现象，但预计对BDT和材料去除过程的机理理解也可以转移到其他陶瓷系统的精密加工中。此外，我们期望对导致部分高变形性和塑性流动行为的物理现象有一些非常基本的了解，这些现象是许多陶瓷在纳米压痕和纳米凹陷条件下的共性。

Diamond cutting of hard and brittle ceramics offers several advantages over other machining methods, like for example grinding. However, it is also a is a technological challenge, because it requires a precise knowledge about the mechanisms of material removal to guarantee a stable process and a high-quality surface finish. While most ceramics behave in a completely brittle manner in macroscopic tests, micromechanical testing frequently reveals some ductility of the material. During diamond cutting such a brittle-ductile transition (BDT) can be observed, depending on the process parameters. It has been shown in the literature that operating the diamond cutting process in the ductile regime is of advantage, because it leads to an ultra-low surface roughness of the machined part. In the proposed research project, the diamond cutting process of silicon carbide (SiC) ceramics will be investigated on all relevant length scales with a combination of scalebridging material and process modeling and in-situ and ex-situ experiments. SiC is chosen as material because its applications in optical devices require an extremely high surface quality. Yet, the high hardness and brittleness of this ceramic poses enormous challenges to the process that can only be mastered if a fundamental insight into the mechanisms of material removal is gained. Consequently, the first objective of this research project is to study the mechanisms of the BDT in SiC under the conditions of diamond cutting. Furthermore, this project will result in a new understanding of the mechanisms of material removal during precision machining in both, the brittle and in the ductile regime, with an emphasis on the ductile material removal processes. As second objective of this project, the gained understanding and the developed scalebridging models will be applied to support process innovations to achieve a surface roughness of less than 10 nm during precision machining of SiC. Such a high machining precision can only be accomplished by a very detailed understanding of the underlying mechanisms and by using numerical models and key experiments to design the required tools. A key issue will be to control the precision machining process such that only ductile material removal takes place because this will produce better surface qualities. Hence, the fundamental part of the project is a necessary requirement to establish this kind of process innovation. While it is the nature of this project to describe rather material specific phenomena for the SiC system, it is expected that the achieved mechanistic understanding of the BDT and the material removal process can be transferred to precision machining of other ceramic systems, as well. Furthermore, we anticipate to gain some very fundamental insight into the physical phenomena that cause the partially high deformabilities and plastic flow behavior that are generic for many ceramics under conditions of nanoindentation and nanoscratching.