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

• Applicant: Professor Dr. Alexander Hartmaier
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Metal-Cutting and Abrasive Manufacturing Engineering
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392230176

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.

• DFG Programme: Research Grants
• International Connection: China
• Partner Organisation: National Natural Science Foundation of China
• Co-Investigators: Dr.-Ing. Hamad ul Hassan; Privatdozentin Dr. Rebecca Janisch; Dr.-Ing. Janine Pfetzing-Micklich
• Cooperation Partner: Professor Dr. Junjie Zhang