EHTT2022-Material removal characteristics of single crystal 4H-SiC based on varied-load nanoscratch tests

Abstract

The single crystal silicon carbides (SiC) have been widely applied in the extreme circumstances and conditions for their excellent physical and chemical properties. In order to obtain various components with high surface integrity and low surface damage, precision and ultra-precision machining methods were used to process single crystal SiC. However, as typical hard-to-machine materials, their good mechanical properties also resulted in the surface defects and subsurface damage. For improving the machining quality and prolonging the service life of components, the varied-load nanoscratch tests were systematically performed on single crystal 4H-SiC by a nanoindenter system with Berkovich indenter in this paper. The characteristics of material removal under different plane, indenter direction, normal loading rate and scratch interval were discussed. The surface morphology of nanoscratch grooves, the distribution of cracks, material deformations and fractures, and cross-section characteristics were analyzed by SEM and 3D profilometer. The mechanism of material removal and crack propagation of single crystal 4H-SiC were also studied. The results indicated that the Si-plane of single crystal 4H-SiC and indenter direction of edge forward were more suitable for material removal and machining. The normal loading rate had little effect on scratch depth, but the lower one would increase the ductile region and critical depth of transition. The increasing of scratch interval would postpone the greater fluctuation of depth-distance curves of second scratch, and curve changes showed high coincidence gradually. In addition, the propagation and interaction of radial, median and transverse cracks resulted in the material fractures and accumulation of chips. The proposed research provides the instruction to high efficiency and precision machining of single crystal SiC for the purpose of emission and carbon reduction.