Mechanisms of brittle-ductile transition and material removal in diamond cutting of silicon carbide
Metallurgical, Thermal and Thermomechanical Treatment of Materials
Metal-Cutting and Abrasive Manufacturing Engineering
Final Report Abstract
The Sino-German cooperation project “Mechanisms of brittle-ductile transition and material removal in diamond cutting of silicon carbide” (DiaCut) had the objectives to increase our understanding of the fundamental mechanisms of diamond cutting of cubic silicon carbide (3D SiC). This material is characterized by a brittle behavior with very limited possibilities to deform plastically, which is typical for all ceramics. Yet, in this project, it could be shown that for concentrated compressive loads, as they occur in nanoindentation, some limited plastic deformation is possible, resulting in a distinct remaining impression on the indented surface and even in a pile-up of the material at the edges of the indented region. If the indentation depth is too large, however, cracks occur during unloading due to residual tensile stresses around the plastically deformed region. This behavior is reflected in the machining behavior of the material, that exhibits a pronounced transition between ductile cutting at small depths of cut and brittle cutting at larger cutting depths. While the former process results in a smooth machined surface, the latter yields not only a large surface roughness but also vertical cracks in the machined surface and has to be avoided to produce a high-quality surface. In this project, a combination of nano-mechanical experiments with in-situ and ex-situ cutting experiments and scale-bridging material modeling was successful in explaining the different mechanisms of material removal in ductile and brittle cutting modes. During ductile cutting, occurring at small cutting depths, the limited plastic deformability of the material is sufficient to produce a smooth cutting process. If the cutting depths exceeds a critical value, however, the material cannot accommodate the distortions imposed by the cutting tool, which results in high stresses causing the 3C SIC material to fracture in a brittle way. Consequently, the material is removed in irregular chunks, yielding a rough machined surface with vertical cracks. The main results of the part of the project conducted at RUB are: • Atomistic simulations revealed that plastic slip in 3C SiC crystals occurs on the <110>{111} slip planes, similar to fcc metals. Furthermore, it could be seen that the dominating phase transformation occurring under the high compressive stresses in front of a cutting edge is the transformation to a thin amorphous layer, whereas other phases of SiC have not been seen. However, this result might be influenced by some deficiencies of the interatomic potentials available for this material and, thus, needs to be confirmed experimentally. • A crystal plasticity model combined with a cohesive zone model could be fully parameterized for 3C SiC by nano-indentation results and atomistic data. This constitutive model revealed good predictive capabilities concerning plasticity and cracking under various indentation loads. • A simpler and numerically more efficient Drucker-Prager model combined with a damage model describing material separation during diamond cutting was able to reproduce the brittle-ductile transition during diamond cutting. While the plasticity parameters could again be determined from nano-indentation results, the parameters of the damage model could only be fitted to reproduce the value of the critical cutting depth at which the transition occurs. Thus, more research is needed to understand the damage mechanisms of 3C SiC and to develop a damage model based on physical quantities that can be determined in independent experiments or atomistic simulations.
Publications
- (2020). Amorphization-governed elasto-plastic deformation under nanoindentation in cubic (3C) silicon carbide. Ceramics International, 46, 12470-12479
L. Zhao, M. Alam, J.J. Zhang, R. Janisch and A. Hartmaier
(See online at https://doi.org/10.1016/j.ceramint.2020.02.009) - (2021). Depth-sensing ductile and brittle deformation in 3C SiC under Berkovich nanoindentation. Materials & Design, 197, 109223
L. Zhao, J.J. Zhang, J. Pfetzing-Micklich, M. Alam and A. Hartmaier
(See online at https://doi.org/10.1016/j.matdes.2020.109223) - (2021). Finite Element Modeling of Brittle and Ductile Modes in Cutting of 3C SiC. Crystals, 11, 1286
M. Alam, L. Zhao, N. Vajragupta, J.J. Zhang, A. Hartmaier
(See online at https://doi.org/10.3390/cryst11111286) - (2021). In situ investigation of nanometric cutting of 3C SiC using scanning electron microscope. International Journal of Advanced Manufacturing and Technology, 115, 2299-2312
Tian D, Xu Z, Liu L, Zhou Z, Zhang J, Zhao X, Hartmaier A, Liu B, Song L, Luo X
(See online at https://doi.org/10.1007/s00170-021-07278-x)
