Study on damage characteristics and ablation mechanism in fiber laser trepan drilling of 2.5D Cf/SiC composites

As a new ceramics matrix composite, 2.5D Cf/SiC composite has been a key material in high-temperature parts of aerospace field. However, the commonly used fiber laser drilling process tends to cause ablation damage to composite structures, which subsequently affects their fatigue lives and in-service performance. Understanding the ablation damage mechanism is crucial in controlling the fiber laser drilling process for achieving desired micro-hole quality. This paper studies the damage characteristics and correspondingly reveals the ablation mechanism in fiber laser trepan drilling of 2.5D Cf/SiC composites. It is found that there are obvious cone angles in the exit of the micro-hole at low laser scanning speed. Aiming at the special needle-punched structures of the 2.5D Cf/SiC composites, the ablation damage of the transverse fiber (0°, and 90° fiber) and needle-punched fiber bundles is analyzed by ways of scanning electron microscope (SEM) and energy dispersion spectrum (EDS) elemental analysis. Specifically, the transverse fiber is prone to needle-like, tapered, transverse fracture, longitudinal crack, and bending damage, and the needle-punched fiber bundles easily appear to interfacial debonding and extrusion fracture during the fiber laser drilling. More importantly, the results show that the layered accumulation, adherent morphology, thin shell, and bubble-like morphology are found to be four main mechanisms of recasting layers. The research provides a theoretical basis for achieving the high-quality micro-hole machining of 2.5D Cf/SiC composites with the fiber laser drilling.