SiC/SiC ceramic matrix composites (CMCs) offer an excellent combination of properties at high temperature such as high specific strength, chemical inertness and irradiation tolerance. Those superior properties make CMCs beneficial for use in high-temperature structural applications that are exposed to extreme environments such as aerospace and nuclear energy. However, well machining qualities can hardly be achieved by conventional machining techniques owing to these properties. Laser water jet (LWJ) machining is a promising solution, which is capable of ablating materials with less/no heat defects, well machining precision and consistency. Nevertheless, the machining capacity of LWJ is still limited by the stability of water jet to a great extent. A water layer may form on substrate surface during the impingement of LWJ, which also sets up obstacle for sufficient ablation. Therefore, a novel coaxial helical gas atmosphere is introduced to promote the machining capacity of LWJ in this paper. A theoretical model is established to describe the gas-water two-phase flow field during the ejection and impingement of coaxial gas assisted LWJ (CGALWJ). The influences of gas component and pressure on the stable length of water jet and surface water layer status are analyzed based on numerical simulations and experiments. Scribing experiments are further carried out on CMCs substrates with thickness of 3 mm. Groove with maximum depth-to-width ratio of 13.6 as well as through cutting are realized without the drawing of SiC fibers, formation of recast layer and delamination. The theoretical and experimental results provide solid foundation for the high-quality machining of ceramic matrix composites and other hard-to-process materials.

SiC / SiC陶瓷基复合材料（CMC）在高温下具有出色的性能组合，例如高比强度，化学惰性和辐射耐受性。这些卓越的性能使CMC有利于在暴露于航空航天和核能等极端环境的高温结构应用中使用。然而，由于这些特性，常规的加工技术很难获得良好的加工质量。激光喷水（LWJ）加工是一种有前途的解决方案，它能够烧蚀具有很少/没有热缺陷的材料，并具有良好的加工精度和一致性。然而，LWJ的加工能力在很大程度上仍然受到水射流稳定性的限制。在LWJ撞击期间，水层可能会在基材表面形成，这也为充分消融设置了障碍。因此，本文提出了一种新型的同轴螺旋气氛，以提高LWJ的加工能力。建立了描述同轴气体辅助LWJ（CGALWJ）喷射和撞击过程中气水两相流场的理论模型。通过数值模拟和实验，分析了气体成分和压力对射流稳定长度和地表水层状态的影响。在厚度为3 mm的CMC基板上进一步进行划线实验。最大深宽比为13.6的沟槽以及通过切割实现的沟槽，无需拉伸SiC纤维，形成重铸层和分层。