The ablation behavior and mechanism of nanosecond laser machined SiCf/SiC composite under different assisted gases

Abstract

As a kind of emerging ceramic matrix composites (CMCs), the SiC_f/SiC composite has demonstrated many advantages in the aerospace industry. However, its ultrahigh hardness and local brittleness greatly increase the machining difficulty by conventional methods. In the present research, the nanosecond laser had been employed to machine the SiC_f/SiC composite with different gases (O₂, N₂, and He), single pulse energy, and gas pressure. The laser machined SiC_f/SiC composite surfaces were characterized to reveal the influence of parameters on ablation behavior. The results exhibit that the gas type and single pulse energy influence the ablation of SiC_f/SiC composite significantly. Specifically, the laser ablation efficiency in O₂ gas is relative higher, but the oxidation is evident and the spattering is large. In contrast, the N₂ and He gases decrease the ablation efficiency and spattering, but the oxidation is also eliminated mostly as well. With the increasing of single pulse energy, the laser ablation efficiency, heat-affected zone and spattering enhanced simultaneously. Comparatively, the increased the gas pressure increases the laser ablation efficiency and spattering a little. Except for the slag taken away by gas stream, the active gas realizes the high-efficiency ablation by assisting reaction and vaporization, while the inert gas mainly depends on vaporization. In general, the high-power laser combining with high-pressure O₂ gas might be more appropriate for rough machining of SiC_f/SiC composite, which ensures the ablation efficiency. While the low-power laser with high-pressure inert atmosphere would be the best choice for final machining of SiC_f/SiC composite, which ensures the ablation quality. Such research might give a light on the machining of CMCs by nanosecond laser.