Microstructure evolution and ablation mechanism of SiCf/SiC ceramic matrix composite microgrooves processed by pico-second laser

SiCf/SiC ceramic matrix composites have been widely applied in turbine engine aerospace components with high temperature resistance, high strength, and lightweight performances. Due to the high brittleness and anisotropy, laser-assisted machining acts as a feasible process to improve the machinability of the SiCf/SiC composites. A single-factor experiment was designed to understand the microstructure evolution and ablation behaviors of the microgrooves processed by pico-second laser in this study. The high pulse energy/scanning time and low scanning speed had positive impacts on the depth and width, but negative effect on the three-dimensional surface roughness Sa. Besides, the optimal parameter was 200 kHz repetition frequency. In addition, the microstructure evolution and ablation mechanism under different laser parameters were investigated by the HRSEM, EDS, and XRD analysis. These experimental results showed that the machined microgrooves were covered by a large amount flocculent composed of amorphous SiO2 when the oxidation was weak, and the splashes with the form of amorphous SiO2 and crystal SiO2 under strong ablation conditions. This indicated that the plasma effect transformed to the photothermal effect with enough heat. Meanwhile, a condensate layer occurred in all experiments and a recrystallized SiC layer relied on the microgroove depth controlled by adjusting laser parameters. This work will provide a theoretical basis and practice guidance for laser-assisted machining of the SiCf/SiC composites.