Material Removal Characteristics of Single-Crystal 4H-SiC Based on Varied-Load Nanoscratch Tests

Single-crystal silicon carbide (SiC) has been widely applied in the military and civil fields because of its excellent physical and chemical properties. However, as is typical in hard-to-machine materials, the good mechanical properties result in surface defects and subsurface damage during precision or ultraprecision machining. In this study, single- and double-varied-load nanoscratch tests were systematically performed on single-crystal 4H-SiC using a nanoindenter system with a Berkovich indenter. The material removal characteristics and cracks under different planes, indenter directions, normal loading rates, and scratch intervals were analyzed using SEM, FIB, and a 3D profilometer, and the mechanisms of material removal and crack propagation were studied. The results showed that the Si-plane of the single-crystal 4H-SiC and edge forward indenter direction are most suitable for material removal and machining. The normal loading rate had little effect on the scratch depth, but a lower loading rate increased the ductile region and critical depth of transition. Additionally, the crack interaction and fluctuation of the depth-distance curves of the second scratch weakened with an increase in the scratch interval, the status of scratches and chips changed, and the comprehensive effects of the propagation and interaction of the three cracks resulted in material fractures and chip accumulation. The calculated and experimental values of the median crack depth also showed good consistency and relativity. Therefore, this study provides an important reference for the high-efficiency and precision machining of single-crystal SiC to ensure high accuracy and a long service life.