Materials removal mechanism of single crystalline SiC with laser-induced periodic surface structures (LIPSS)

The surface modification by ultra-fast laser could regulate the mechanical properties of hard and brittle materials. Since silicon carbide (SiC) is too hard to be machined with acceptable removal rate and quality by mechanical abrasives, and femtosecond laser (fs-laser) assisted grinding could be a potential method to improve the machinability of SiC. Under fs-laser modulating, SiC surface could be modified to generate laser-induced periodic surface structures (LIPSS). Understanding the mechanical properties and material removal mechanism of the LIPPS surface is crucial to accomplish a high efficiency and quality machining process. This paper aims to investigate the effects of fs-laser modification on the mechanical properties, removal mechanism, removal efficiency, and microstructure changes of 4H-SiC surface during removal, together with those of the original 4H-SiC surface for comparison. The hardness and elastic recovery ability of the modified layer are determined by nanoindentation test, and the nano-scratch test is adopted to study the materials removal behavior. The removal efficiency and the quality of the modified surface is significantly improved. Phase transformation is observed in the scratching area, which reveals the existence of ductile mode removal. Moreover, the stress distribution and the change of scratching force on the surface of SiC before and after modification are studied by finite element method (FEM). The results show that the stress distribution and transmission when scratched on the modified surface is lower than that of the original surface, and the scratching force under the same scratch conditions is greatly reduced. With the understanding of materials removal behavior from the whole process of deformation, phase transformation, and separation of LIPPS from substrate, then the fs-laser modification of SiC could be evidenced as an effective method to improve the grinding efficiency and quality in mass production of industry.