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

与其他加工方法（例如研磨）相比，硬脆陶瓷的金刚石切割具有多项优势。然而，这也是一个技术挑战，因为它需要精确了解材料去除的机制，以确保稳定的工艺和高质量的表面光洁度。虽然大多数陶瓷在宏观测试中表现为完全脆性，但微观力学测试经常显示材料的一些延展性。在金刚石切削过程中，可以观察到这种脆韧性转变（BDT），这取决于工艺参数。在文献中已经表明，在韧性范围内操作金刚石切削工艺是有利的，因为它导致加工零件的超低表面粗糙度。在拟议的研究项目中，金刚石切割碳化硅（SiC）陶瓷的过程中，将研究所有相关的长度尺度与scalebridging材料和过程建模和原位和非原位实验相结合。选择SiC作为材料是因为其在光学器件中的应用需要极高的表面质量。然而，这种陶瓷的高硬度和脆性对工艺提出了巨大的挑战，只有对材料去除机制有了基本的了解，才能掌握这一工艺。因此，本研究计画的第一个目的是研究在金刚石切削条件下，SiC中BDT的机制。此外，该项目将导致在精密加工过程中的脆性和韧性政权的材料去除机制的新的理解，重点是韧性材料去除过程。作为该项目的第二个目标，所获得的理解和开发的scalebridging模型将被应用于支持工艺创新，以实现在SiC精密加工过程中小于10 nm的表面粗糙度。只有通过非常详细地了解基本机制并使用数值模型和关键实验来设计所需的工具才能实现如此高的加工精度。一个关键的问题是控制精密加工过程，以便只去除韧性材料，因为这将产生更好的表面质量。因此，该项目的基础部分是建立这种工艺创新的必然要求。虽然本项目的性质是描述SiC系统的特定材料现象，但预计对BDT和材料去除过程的机械理解也可以转移到其他陶瓷系统的精密加工中。此外，我们期望获得一些非常基本的洞察物理现象，导致部分高的变形和塑性流动行为，是许多陶瓷的纳米压痕和纳米划痕的条件下通用。

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.