Nanosecond laser ablation behavior of C/SiC composites under water layer protection: Experiments and theoretical investigation

•The nanosecond laser ablation behavior of the C/SiC composites in the air and water environments was investigated.•The mechanism of material removal in two processing environments was systematically analyzed and compared from the perspective of experiments and thermodynamic theory.•The energy balance equation of the laser processing material surface in two environments is established.•The existence of a water layer effectively avoids the redeposition of SiO2 on the processing surface and alleviates heat accumulation, and the processing quality is better. Due to their excellent properties, C/SiC composites have gradually become a high-quality choice for structural parts in aerospace and other fields. However, the manner by which to achieve high-quality and efficient surface micromachining is still the focus of current research. In this study, we explored a new method of underwater nanosecond laser processing of C/SiC composites to obtain a machined surface with high cleanliness, less redeposition, and small heat affected area. The ablation behavior and material removal mechanism in the air and water environments were analyzed and compared by using a variety of characterization methods in combination with thermodynamic theory. The changes of the groove depth, width, surface morphology in different fiber directions, and material composition in the two environments were analyzed. The results showed that the removal of materials is realized by thermochemical corrosion in both environments. The water environment benefits from the cooling function of water layer, which alleviates heat accumulation in the processing area, and the heat affected area is small. Furthermore, the mechanical action of the water layer captured the vast majority of SiO2 produced by oxidation reaction, effectively avoiding its redeposition on the machined surface and improving the surface cleanliness. For C/SiC composites, this work provides a feasible method for high-quality processing.