The Effect of the Infrared Laser Pre-heating on Ultraviolet Picosecond Laser Polishing of SiC Ceramics

The ultraviolet laser has been used to polish SiC ceramics by its thermal and photochemical effect in previous works to resolve the application limitation of the SiC ceramics for the demand of high-precision applications. In this paper, the "cold polishing" technology of SiC ceramics under photon absorption was studied by using the 355nm ultraviolet picosecond laser, the surface roughness was reduced from Ra=1.616μm to Ra=1.087μm only even though the polishing process parameters has been optimized, because the thermal effect such as gasification was found due to the ablation threshold, and the surface quality of brittle ceramics might be degraded by thermal effect during laser polishing. The ablation threshold of the SiC was obtained as about 0.3J/cm<sup>2</sup>. The method of ultraviolet picosecond laser "cold polishing" with infrared laser as preheating source was innovatively proposed to promote the photon-absorption process. By adjusting the preheating process parameters of the infrared laser, the macroscopic morphology and microstructure of polished SiC ceramic surface were analyzed, so as to further clarify the mechanism of photon-absorption effect during the polishing process. It was found that the “cold polishing” by the photon absorption can be promoted owing to the decrease of the ablation threshold under the infrared laser preheating process. Defects such as cracks and porosity cannot be found under the 200× optical microscope, the surface roughness of about 0.66μm can be obtained compared with the 1.087μm by the polishing of ultraviolet picosecond laser. Thus, the ultraviolet picosecond laser polishing with infrared laser preheating technology can be used as the high precise and high efficient polishing technology for the SiC ceramics.