Silicon carbide is an ideal material for advanced electronics, military, and aerospace applications due to its superior physical and chemical properties. In order to understand the effect of crystal anisotropy of 4H-SiC on its processability, nanoindentation and nanoscratch tests on various crystallographic planes and orientations were performed and the results outlined in this paper. The results show that the C-plane of 4H-SiC is more rigid, while the Si-plane is more elastic and ductile. Better surface quality may be obtained on the Si-plane in nanoscale abrasive machining. The maximum lateral force, maximum residual depth of the scratch, and maximum crack width on the C- and Si-planes of 4H-SiC are significantly periodic in crystallographic orientations at 30° intervals. The scratch along the direction is more prone to crack expansion, and better machined surface quality is easy to obtain along the directions of C- and Si-planes.

OH* generated through plasma catalysis offers several advantages, including a long survival time, high modification efficiency, and environmental friendliness. Consequently, a plasma-assisted polishing technology has rapidly developed. Previous studies exploring the interaction mechanism between OH* and 4H-SiC have often assumed flat surfaces. However, in the surface modification experiments on 4H-SiC, the actual surface morphology was not flat but contained numerous scratches. Therefore, this study investigated the interaction mechanism of OH* on an uneven surface using reactive force field molecular dynamics (ReaxFF MD) simulations. The results show that in the low-speed OH* modification process, the adsorption effect leads to a thicker modified layer at higher locations than at lower locations. The resulting modified layer can be removed by soft abrasive mechanical polishing to achieve surface flatness, but there will be a modified layer on the surface, which needs to be modified and polished several times. In contrast, during high-speed OH* modification, high-speed particle bombardment causes more Si-O bonds to diffuse into the scratches, resulting in the formation of a flat bonding layer with surface planarization achieved after a single polishing step. The interaction mechanism of OH* with the uneven surface at different speeds, as obtained through ReaxFF MD, provides a theoretical foundation for subsequent polishing experiments.