Hybrid approach combining femtosecond laser finishing with ultrasonic assistance to improve surface integrity of picosecond-processed SiC ceramics

Picosecond laser processing of silicon carbide (SiC) ceramics inevitably causes severe thermal damage, including surface porosity, microcracks, and a thick recast layer. This study proposes a hybrid finishing strategy that combines high-efficiency picosecond rough processing with femtosecond laser finishing, followed by ultrasonic vibration assistance, to further improve surface integrity. The results demonstrate that femtosecond laser processing with a threshold multiplication factor of 6–12 operates in the low-thermal-damage regime, enabling sequential removal of the recast layer and progressive elimination of inherited microcracks, a removal behavior consistent with Coulomb-explosion-mediated ablation. Ultrasonic assistance at a moderate amplitude enhances debris clearance, likely via acoustic streaming, and may promote mechanical detachment of the residual damage layer, yielding a thinner, more continuous recast layer with significantly reduced subsurface porosity compared with non-assisted conditions. Excessive laser power with a threshold multiplication exceeding approximately 12 induces thermally dominated ablation consistent with phase explosion and re-oxidation, while high ultrasonic amplitude causes mechanical disruption. This approach establishes a processing window for high-quality processing of hard-brittle ceramics, with optimal parameters identified for low-thermal-damage finishing and ultrasonic assistance.