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.

In order to study the anisotropy of fracture toughness and fracture mechanism of single-crystal sapphire, the three-point bending tests and the single-edge V-notch beam (SEVNB) were used to test the fracture toughness of A-plane, C-plane, and M-plane sapphire, which are widely used in the semiconductor, aerospace, and other high-tech fields. Fracture morphology was investigated by a scanning electron microscope and three-dimensional video microscopy. The fracture toughness and fracture morphology of different crystal planes of sapphire showed obvious anisotropy and were related to the loading surfaces. C-plane sapphire showed the maximal fracture toughness of 4.24 MPa·m^1/2, and fracture toughness decreases in the order of C-plane, M-plane, and A-plane. The surface roughness is related to the dissipation of fracture energy. The surface roughness of the fracture surface is in the same order as C-plane > M-plane > A-plane. The fracture behavior and morphology of experiments were consistent with the theoretical analysis. C-plane sapphire cleavages along the R-plane with an angle of 57.6 degrees and the rhombohedral twin were activated. M-plane and A-plane sapphire cleavages along their cross-section.

A small cutting depth is the key parameter to realize precision in the machining process. The stability of the machining process will directly affect the quality of machining. In this study, dry grinding experiments using an Fe-Cr-Co permanent magnet alloy with small cutting depths (5 μm) were carried out. The relationship between the number of peaks and valleys and the quality control of the grinding force, wheel speed and feed speed were analyzed. The relationship between the peak and valley values of the grinding force signals and the peak and valley values of the grinding surface obtained using a white light interferometer was revealed. The influence of the grinding parameters on the grinding forces was analyzed by processing the grinding force signals with a low-pass filter based on the rotational speed of the grinding wheel. The experimental results indicated that the difference in grinding force between the peak and valley could be reduced by increasing the grinding wheel speed, which was mainly due to a decrease in average grinding force when the maximum undeformed cutting thickness of the single abrasive decreased. The actual height difference between the grinding surface peak and valley could be realized by increasing the grinding wheel speed. The feed speed of the worktable had no effect on the grinding force signal and the peaks and valleys of the surface morphology. Lower surface roughness could be achieved by reducing the feed speed and increasing the grinding wheel speed.

The surface integrity of grinding has a significant influence on the service performance and life of machined parts. In this study, the influence of grinding parameters and the grit size of the grinding wheel on the surface integrity of the hardened steel, including the roughness, microstructure, and hardness of the subsurface and the residual stress of the ground surface, was comprehensively investigated, and the corresponding mechanisms were revealed. The results show that the roughness perpendicular to the grinding direction was significantly larger than that parallel to the grinding direction due to serious side flow, and increasing the grinding speed or reducing the grinding depth was beneficial for reducing the side flow and thus decreasing the roughness. It was found that the grinding temperature dominated the formation of a harder white layer and a softer black layer, and workpiece speed had the smallest effect on the transition of subsurface microstructure compared to grinding speed and depth. It was also found that the increase in workpiece speed, grinding depth, or grinding speed resulted in a transition from compressive to tensile residual stress or an increase in tensile residual stress, and that grinding wheels with finer grit tended to induce compressive residual stress. This study may help to improve surface integrity by optimizing grinding parameters or facilitating the selection of the optimal grinding wheel.

Electrical discharge machining (EDM) is an efficient method for processing silicon carbide (SiC) substrates. However, the chemical modification mechanism of SiC substrates in the EDM process remains not fully elucidated. To clarify the material removal mechanism of SiC substrates in EDM, this study investigated the behaviors of SiC substrates under different discharge conditions through experimental analysis and interface temperature field simulation. Results indicate that the SiC substrates sequentially exhibit characteristic morphologies of surface oxidation, thermal decomposition, and fracture as discharge energy increases. A discolored layer composed of amorphous SiO₂ is formed on the SiC surface in low-discharge energy. Crystalline silicon and graphitic carbon are generated from the thermal decomposition of SiC substrates in high-discharge energy. Excessively high discharge energy induces the breakdown of SiC substrates. A critical temperature threshold is identified that delineates the initiation of prominent thermal oxidation on the SiC surface. Temperature field simulations further reveal the correlation between EDM parameters and interfacial temperature variations, along with the mechanisms of material removal driven by thermal diffusion. This study deepens the fundamental understanding of the EDM removal mechanism of SiC substrates and is expected to provide a scientific basis for the efficient material removal of SiC substrates.