SiC/SiC ceramic matrix composites (CMCs) are widely applied in the aerospace and nuclear industries due to their excellent material nature (strength, hardness, and irradiation tolerance) at high-temperature loads. However, high-quality machining cannot be easily realized because of the anisotropic material structure and its properties. In this study, a laser water jet (LWJ) was adopted for CMCs machining. Firstly, the finite element model (FEM) was established describing a representative three-dimensional microstructure including weft yarn, warp yarn, SiC base, and the pyrolytic carbon (PyC) fiber coating. The temperature distribution, as well as its evolution rule on substrate surface under LWJ machining, was analyzed. Moreover, a single-dot ablation test was carried out to verify the accuracy of the numerical simulation model. Secondly, the variation in maximum temperatures under different laser pulse energy was obtained by means of FEM. Nonetheless, a non-negligible deviation emerged in the ablation depth of the numerical calculation and experimental results. Although the simulation results were obviously superior to the experimental results, their proportions of different machining parameters reached an agreement. This phenomenon can be explained by the processing characteristics of LWJ. Finally, single-row and multi-row scribing experiments for CMCs with 3 mm thickness were developed to clarify the processing capacity of LWJ. The experimental results indicated that single-tow scribing has a limiting value at a groove depth of 2461 μm, while complete cutting off can only be realized by multi-row scribing of LWJ. In addition, the cross-section of CMCs treated by LWJ presented a surface morphology without a recast layer, pulling out of SiC fibers, and delamination. The theoretical and experimental results can offer primary technical support for the high-quality machining of CMCs.

In this study, the novel coaxial-annulus-argon-assisted (CAAA) atmosphere is proposed to enhance the machining capacity of the water-jet-guided laser (WJGL) when dealing with hard-to-process materials, including ceramic matrix composites (CMCs) and chemical-vapor-deposition (CVD) diamond. A theoretical model was developed to describe the two-phase flow of argon and the water jet. Simulations and experiments were conducted to analyze the influence of argon pressure on the working length of the WJGL beam, drainage circle size, and extreme scribing depth on ceramic matrix composite (CMC) substrates. A comparative experiment involving coaxial annulus and helical atmospheres revealed that the coaxial annulus atmosphere disrupts the water jet proactively, while effectively maintaining the core velocity within the confined working length and enhancing the processing capability of the WJGL beam. Single-point percussion drilling experiments were performed on a CMC substrate to evaluate the impact of machining parameters on hole morphology. The maximum depth-to-width ratio of the groove and depth-to-diameter ratio of the hole reached up to 41.2 and 40.7, respectively. The thorough holes produced by the CAAAWJGL demonstrate superior roundness and minimal thermal damage, such as fiber drawing and delamination. The average tensile strength and fatigue life of the CMCs specimens obtained through CAAAWJGL machining reached 212.6 MPa and 89,463.8 s, exhibiting higher machining efficiency and better mechanical properties compared to femtosecond (194.2 MPa; 72,680.2 s) and picosecond laser (198.6 MPa; 80,451.4 s) machining. Moreover, groove arrays with a depth-to-width ratio of 11.5, good perpendicularity, and minimal defects on a CVD diamond were fabricated to highlight the feasibility of the proposed machining technology.

Monocrystalline silicon has shown great potential in constructing advanced devices in semiconductor, photoelectric, and photochemistry fields. The fabrication of micro-grooves with large depth-to-width ratio (DTWR) and low taper is in urgent demand as this type of groove can significantly promote the device performance. The grooves with such characterizations can hardly be achieved by conventional machining techniques owing to the high hardness and brittleness of silicon. Laser waterjet (LWJ) machining is a promising solution, which is capable of ablating materials with less or no heat defects, well machining precision, and consistency. Therefore, this paper firstly established a theoretical model describing the interaction between silicon and LWJ. Through the numerical simulation, the evolution of temperature and stress distribution at the machining region was analyzed. Variation experiments were carried out correspondingly. On these bases, scribing experiments were put forward aimed at discovering the influence of machining parameters on groove morphology. Optimized scribing strategy which is capable of realizing the construction of a micro-groove with DTWR of 19.03 and taper of 0.013 was obtained. The results contributed to the understanding of LWJ processing of silicon on a small scale as well as broadening the application prospects of LWJ for treating other semiconductor devices.