Laser processing has the advantages of controllable energy, no contact, high efficiency, and high precision. It has good application prospects in the processing of hard and brittle materials, such as SiC ceramics. In this study, a new multi-beam coupled laser processing platform was used to polish SiC ceramics by adjusting the bidirectional spot overlap rate (δ) and energy density (E_D) of the multicoupled laser. The effects of the multibeam coupled laser energy density and bidirectional spot overlap rate on the surface morphology, roughness, phase change, and element distribution of SiC ceramics were systematically investigated. The material removal mechanism of SiC ceramic laser processing was revealed. This study can provide a technical support for optimizing the laser polishing process of SiC ceramics.

First, a multibeam coupled nanosecond laser was used to polish SiC ceramics under different process parameters. Then, laser confocal microscopy, Raman spectroscopy, scanning electron microscopy, and other test methods were used to analyze the microstructure, phase change, and element distribution of SiC ceramics. The removal mechanism of SiC ceramic materials using the coupled laser and the effects of various parameters on surface quality were analyzed from multiple perspectives.

The multibeam coupled laser focal point shows a Gaussian-like energy distribution [Fig. 2(a)], with a broader and more uniform effective action surface on the material within the spot and a smaller heat-affected zone (Fig. 3). The polished surface shows a more pronounced color shift at the macroscopic level [Fig. 4(a)] when δ and E_D are low. The polished area is dull gray-black and gradually changes to a slightly brighter metallic color as δ and E_D increase. The polished surface microstructure (Fig. 5) appears relatively flat compared with the original surface microstructure [Fig. 4(b)], and the polished surface roughness decreases to 0.73 μm when E_D is 4.254 J/cm², δ is 75%, and the number of scans is two [Fig. 8(b)]. However, the occurrence of edge stacking attributed to many recast layers is not conducive to further improvement of the surface quality. The characteristic peak of the Si singlet appears in the Raman spectral curve of the polished surface recast layer (Fig. 9), indicating that a violent photochemical reaction accompanies polishing. Chemical bond breaking and reorganization occur, alleviating the problem of excess free carbon on the surface (Figs. 10 and 12) and introducing oxygen elements when δ and E_D are extremely high. This is owing to the extended temperature span of the laser action region, leading to thermal stress inside the surface material, which in turn, generates microcracks from the pore edge to the surrounding area (Fig. 11).

In this study, a new multi-beam coupled nanosecond laser was used to polish SiC ceramics. The effects of the laser bidirectional spot overlap rate and energy density on the macroscopic and microscopic morphologies, roughness, phase, and element evolution of the polished surface were investigated. The results show that the violent photochemical reaction significantly alleviates the problem of excessive surface free carbon when δ and E_D are high, the surface morphology of the material becomes smooth, and the surface roughness decreases. However, this results in the formation of many recast layers on the surface when E_D is very high, which is not conducive to further reduction of surface roughness.