An experimental investigation of scan trajectory into the underwater femtosecond laser polishing SiC ceramic

Silicon carbide (SiC) ceramics, due to their excellent mechanical properties and oxidation resistance at elevated temperature, have a widespread application in microelectronics and aerospace. However, the machining of SiC ceramics into the desired structural ceramic components presents a challenge because of their high hardness and high brittleness. In this paper, a novel method of underwater femtosecond laser polishing SiC ceramics was proposed. We investigated the influence of scan trajectory, such as scanning pitch and polishing mode, and femtosecond laser pulse energy on surface roughness and polishing depth during underwater polishing processing. The experimental results indicated that the polishing depth decreased with the increasing scanning pitch, and then tending to saturate. A deep cavity was obtained under the condition of high laser pulse energy and small scanning pitch during polishing. However, the obtained surface quality was rough at this condition, which could be used for rough polishing operation because the high material removal rate is the primary concern. In addition, the cross-scanning polishing mode achieved the better surface quality without cracks and pits than the transverse polishing mode, but the polishing efficiency was low. In addition, under appropriate machining conditions, the smooth polished surface with surface roughness 0.76 µm was obtained by using 15 µm scanning pitch together with high laser pulse energy and cross-scanning polishing mode.