气膜孔ZrO2陶瓷热障层放电辅助化学加工机理与扫描工艺

Cooling gas ejected from film cooling holes can form the gas film on a wall for heat insulation and heat dissipation, and this technology is applied to protect turbine blades of aero engine to operate within the environment of extreme high temperature. In order to further achieve the high thrust-weight ratio and high efficiency for the next generation of aero-engines, the turbine blades made from high temperature alloy will be designed with the thermal barrier coating (TBC) of the high-temperature ceramic that is high hardness material and hard to processing, which makes the machining of film cooling holes with the structure of compound-angle outlet become more difficult. It is expecting an online integrated process for the defect-free machining of the complex-structure film cooling holes through the blade wall made of the composite material. Based on feasible consideration of the integrating process, the machining mechanism of spark assisted chemical engraving (SACE) will be researched on the workpiece material of ZrO2-ceramic TBC, and a novel scanning process will be explored for machining the irregularly shaped outlets without surface-and-interfacial damage. The research emphasis is laid on the material removed mechanism of the tetragonal / cubic ZrO2 ceramic mixed with nanoparticles and micro pores. Considering the processing conditions of scanning motion and micro machining gap, the action mechanism and controllable principle will be researched on the procedures of the electrolytic bubbles pattern, the electric discharge effects in the bubbles, and the chemical erosion of ZrO2 ceramic and NaOH solution under the high temperature and high pressure of the discharge effects. Furthermore, the process problems will be solve hopefully including the effectively sensory feedback of micro machining gap, the scanning strategies associated with defect-free energy, etc. It is expected to achieve an efficient process for precisely forming the defect-free TBC outlets.

气膜孔用以喷出冷却气体形成壁面气膜来隔热散热，保护航空发动机涡轮叶片在极端高温下工作。下一代航空发动机为达到更高推重比和效率，高温合金叶片上将设计有难加工的高硬度且耐高温的陶瓷热障层，这更增加了带有复合角出口结构气膜孔的加工难度，有待一种无损伤加工复合材料复杂结构气膜孔的在线集成工艺。本项目考虑这种集成可行性，拟研究ZrO2陶瓷热障层放电辅助化学加工（SACE）机理，探索一种无表面/界面损伤的热障层复合角异形孔口扫描加工新工艺。重点研究这种混有纳米颗粒、微小孔隙的四方/立方相ZrO2陶瓷的材料剥离机理；拟揭示扫描运动及微小间隙作用下电解气泡形态及其内瞬间放电效应、以及此高温高压效应下ZrO2陶瓷与NaOH溶液化学反应蚀除的作用机制和可控规律。进而拟解决微小加工间隙有效传感反馈、无损伤能量关联的扫描策略等工艺问题，有望形成一套精确成形且无微观损伤的高效工艺。

气膜冷却技术保护航空发动机涡轮叶片在极端高温下工作。为进一步提高耐高温性能，先进涡轮叶片表面设计有陶瓷热障层。本项目面向氧化锆陶瓷热障层上气膜孔异形孔口无损伤扫描加工，阐明氧化锆陶瓷放电辅助化学加工（SACE, spark assisted chemical engraving）的作用机理，得到工件材料去除规律和优化加工工艺。主要研究内容和重要结果：.1、提出并验证了氧化锆陶瓷SACE固液产物反向佐证加工机理的方法。①分析得到氧化锆在不同物理及化学条件下相变路径。②实验发现：晶态屑证明热力冲击崩碎、放电高温融合的物理去除存在性，无定形态屑证明氧化锆与NaOH溶液化学反应蚀除存在性。③国内外首次实现较为准确获得物理去除和化学蚀除的量化比例。.2、仿真和高速摄像机观测实验研究了SACE微观过程机理。①离子碰撞反应仿真得到了工具电极表面电解氢气膜放电击穿过程和关键工艺参数定性影响规律。②建立了气泡生长速率、放电密度百分比、放电分布均匀性和气泡破裂频率作为定量评价指标。③高速摄像观测得到了加工电压、浸液深度关联工具电极表面气膜变化影响击穿放电的微观瞬时特性。.3、实验发现了工具电极端部放电集中现象、接触去除效应，建立了能量传递过程模型。①阐明了物理去除和化学蚀除的作用能量差异性，得到了化学蚀除主导无损伤加工的必要条件。②阐明了加工间隙敏感的原因。③提出并验证了多棱边/粗糙表面工具电极、微薄层流电解液的约束放电方法，提高了加工效率和成形精度。.4、完善了加工实验装备，开展了关键工艺因素影响规律、工艺优化方法研究。①发明了间接式电接触反馈的绝缘材料表面高度测量方法，用于实现氧化锆陶瓷工件表面高度标定与调平。②发明了浸液深度精确调控方法。③提出旋转振动断弧方法，有效避免热障层和合金基体界面击穿电弧的不利现象。④提出并验证了柔性工具电极微力接触的扫描优化工艺。⑤提出并初步验证了高温合金基体气膜孔异形孔口分块成形工艺。

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