Influence of assisted gases and parameters on quasi-continuous wave laser drilling of high aspect ratio micro-holes in SiCf/SiC composite

In the present research, a coaxial gas assisted Quasi-continuous wave (QCW) laser was applied to machine micro-holes with high aspect ratios in SiC f /SiC composites. By regulating the gas type and laser parameters, it aims to optimize the micro-hole quality and explore the underlying influence mechanisms. The results exhibit that reactive gases (air and O 2 ) enhance ablation and promote surface oxidation, increasing micro-hole taper angle. Whereas, non-reactive gases (N 2 and He) restrain the excessive ablation and surface oxidation, decreasing micro-hole taper angle. Comparatively, the N 2 -assisted QCW laser drilling achieves a balance among micro-hole shape, surface roughness and economical efficiency. In N 2 -assisted QCW laser drilling, an increasing in single pulse energy enlarges the micro-hole diameter, but it also increases the taper angle and surface reaction products. Conversely, a reduction in pulse width results in smaller micro-hole diameters and lower taper angles. Additionally, the coaxial gas stream generates small molten debris which subsequently redeposits on wall surfaces. The micro-hole fabricated by N 2 -assisted QCW laser drilling could be categorized into three segments. In the upper segment, the predominant characteristics include a taper shape and fine lamellar reaction products, attributed to enhanced thermal diffusion conditions and prolonged gas reheating. The middle segment is marked by a uniform diameter and predominantly spherical reaction products. In contrast, the bottom segment shows a transformation from spherical reaction products to irregularly shaped reaction products, which correlates to varied reheating time. The present research might enlighten the new laser drilling process for micro-holes in SiC f /SiC composites.