Surface and subsurface evolution mechanism in continuous wave laser ablation process of Cf/SiC ceramic matrix composites: A multiscale investigation

Abstract

Due to the excellent material properties, ceramic matrix composites (CMCs) are increasingly favored in aerospace and other high-performance applications. As the industry advances, both the reinforcement and matrix materials tend to be more difficult to machine. Laser-based processing methods are becoming increasingly popular. However, the underlying mechanisms and the formation of surface integrity in such complex materials remain unclear. At present, the overall ablation process of complex CMCs has not been studied. To address these gaps, this study investigates the surface integrity induced by laser ablation and its underlying mechanisms of CMCs. The results reveal that post-ablation surface morphologies vary significantly across different regions of Cf/SiC CMCs—those with vertically oriented fibers, where the height is relatively high, and those with horizontally oriented fibers, where the height is comparatively low. At a scanning speed of 400 mm/min, the laser energy corresponding to a power of 3 kW can be regarded as the threshold between rough and fine machining. It was further clarified that the spherical particles formed on the ablated surface were composed of elemental silicon rather than the commonly assumed oxides. The surface region exhibited a loose four-layer structure consisting of silica, elemental silicon, silicon carbide, and a pyrolytic carbon layer. In addition, a typical multi-layered surface structure—arising from the superior thermal conductivity of the fibers—was also observed on the surfaces of fibers located within the subsurface region of the workpiece. A model of the temperature distribution was established to elucidate how differences in thermal conduction induced by fiber orientation influence the ablated surface morphology of the CMC. Overall, these findings comprehensively explain the ablation process, surface integrity evolution, and underlying mechanisms of CMCs subjected to laser ablation.