Femtosecond laser processing method for conical holes in SiC_f/SiC composites

Ceramic matrix composites stand out for excellent mechanical properties and high temperature resistance, making them promising for hot-end components of aircraft engines. However, due to their high hardness, brittleness, and low conductivity, processing conical film cooling holes with small aperture, large aspect ratio, and variable cross section has become a challenge. Femtosecond laser processing is an effective solution to this problem. Based on the conical hole structure, both positive and negative helical path were designed, and a two-step rotary drilling method using an inclined laser beam is adopted to achieve high-quality machining of positive and negative conical holes in SiC_f/SiC composite materials. The dimensional error of the conical hole entrance and exit is ≤ 10 μm, and the taper error is ≤ 0.1°; the entrance edges were covered with a small amount of deposition, while the exit is free of deposition and has sharp edge. The wall morphology of both the positive and negative conical holes is uniform, with fibers and matrix structures uniformly removed. The surface roughness (Sa) of the hole walls is approximately 1.8 μm for the positive conical hole and 2.5 μm for the negative conical hole. The formation process of the conical holes is studied, and the evolution of the bottom morphology and entrance/exit dimensions is analyzed. The hole profile formation mechanism is clarified, providing a processing foundation and quality evaluation reference for high-quality machining of conical holes in SiC_f/SiC composite hot-end components.