One-step in-situ low damage etching of SiC/SiC composites by high-temperature chemical-assisted laser processing

Abstract

SiC/SiC composites have a promising application prospect in the fields of aero-engine turbine blades and other hot-end components due to their excellent properties. It is difficult to machine SiC/SiC composites by traditional mechanical processing because of the ultra-high hardness and anisotropic character. The routinely laser direct processing in the air produce thermal effect damage, resulting in heat-affected zones and microcracks. Here high-temperature chemical-assisted nanosecond laser processing was investigated to realize one-step in-situ fast etching without causing damage to the structure of SiC/SiC composites. Firstly, the chemical wet etching only occurred in the laser-induced local high-temperature region. There was no additional etching damage to the substrate material in the region where the temperature was relatively low. Secondly, chemical liquid served as a transparent constraint layer, the ablation pressure on the material increased in a liquid confined environment. In comparison with laser direct etching in the air, the exposed fiber was not a needle-like structure and tubular structure but turned into a thin and flat tongue-like structure. The etching behavior of 0° fiber layer, 90° fiber layer, and crossing regions of fibers of different directions at low and high laser intensities were studied. Further, the hardness and friction coefficient of SiC/SiC composites after laser direct etching in the air and high-temperature chemical-assisted laser etching were compared. The chemical elementary composition before and after etching was measured to reveal the oxidized and carbonized characteristics. It was concluded that the action mechanism was the combined result of high-temperature decomposition, laser-induced ablation pressure in the liquid confined region, and local chemical wet etching. The results demonstrate that high-temperature chemical-assisted laser etching has some advantages over traditional laser beam machining and is a potential processing method for SiC/SiC composites.