多材料光固化技术制备夹层结构氮化硅的成形机理与精度调控机制

The radome with C-type sandwich structure is one of the most potential radomes for hypersonic missiles due to its compact surface and high porosity core. However, it is difficult to directly fabricate near-net-shaped and high-precision radome with the structures mentioned above via conventional manufacturing process. In this project, two types of ceramic paste will be prepared based on sub-micron silicon nitride powder and micron silica poly-hollow microsphere, respectively. Multi-materials deposition will be achieved by utilizing screw extruding mechanisms, and accurate selective area exposure will be achieved through DMD chip, so as to fabricate the high precision silicon nitride ceramic with the sandwich structure. In view of two key scientific issues, the Stereolithography forming mechanism of ceramic pastes under the effect of heterogeneous interfacial tension, and control mechanism of interlayer stress resulted from the difference of curing rate and densification rate of multi-materials, the following researches will be performed respectively. The rheological properties, curing property and wetting property of the ceramic paste and their regulation mechanism are intended to be studied. The SLA forming mechanism of the heterogeneous interface and the regulatory mechanism of forming accuracy of ceramic pastes will be revealed. Polymerization kinetics and stress regulation mechanism of multi-material SLA forming will be expounded. Regulation mechanism of the microstructure, phase composition, mechanical and dielectric properties by gas-pressure sintering kinetics of silicon nitride will be clarified. This project is expected to break through the manufacturing bottleneck of silicon nitride with sandwich structures, providing theoretical basis and technology support for multi-material, multi-structures and high precision Stereolithograghy. Meanwhile, it plays a driving role in the development of hypersonic aircraft.

C型夹层结构氮化硅天线罩由于表层致密、芯层高孔隙率而成为最具潜力的高超音速导弹天线罩之一。然而，传统加工工艺难以直接近净成形出上述结构的天线罩。本项目基于亚微米氮化硅粉末与微米氮化硅聚空心球制备两种陶瓷膏体，通过螺杆挤出喷嘴进行多材料涂布，利用数字微镜芯片精确选择曝光区域，实现夹层结构氮化硅的精确成形。针对陶瓷膏体异质界面张力作用下的光固化成形机理，以及陶瓷膏体固化速率和致密化速率差异产生层间应力的调控机制两个关键科学问题，本项目拟研究陶瓷膏体流变性能、固化性能、润湿性能的调控机制；揭示陶瓷膏体异质界面光固化成形机理与成形精度控制机制；阐明多材料光固化成形聚合动力学与应力调控机制；澄清氮化硅气压烧结动力学对微观结构、相组成和性能的调控机制。本项目有望突破夹层结构氮化硅加工瓶颈，为多材料、多结构陶瓷高精度光固化成形奠定理论基础和提供技术支持；同时，对高马赫数飞行器发展起到推动作用。

攻防战争中，为了有效避免敌方防空反导系统的拦截，超声速飞行器朝着高马赫数方向发展，并对其天线罩提出承载、防热/隔热、透波多功能一体化的要求。氮化硅 (Si3N4) 陶瓷是最具潜力的高温透波材料之一，为了获得足够的力学强度、良好的防热/隔热效果以及超宽频带透波，Si3N4被设计为多孔夹层结构。然而，传统制造工艺难以其加工。本项目采用光固化成形技术制造多孔夹层，聚焦Si3N4的成形机理、缺陷调控机制，以及微观结构和力学性能调控开展研究，并获得以下重要结论：KH560易与丙烯酸类预混液桥接，使得亚微米氮化硅在预混液中分散效果更为显著，提高陶瓷浆料的流变性能与稳定性。同时改性氮化硅与EA之间形成的醚共价键降低浆料的表面张力，改善浆料对已固化层的润湿性。最终在氮化硅表面形成EA薄壳，显著降低陶瓷粉体与预混液间的折射率差，提高陶瓷浆料的固化性能，实现氮化物陶瓷的光固化成形。然而，光固化Si3N4陶瓷成形精度、层间缺陷和层间应力取决于曝光时间和切片厚度共同作用的结果：随着曝光时间延长，C=C双键转换率增大，同时二次曝光现象增强，成形精度降低，层间应力增大；当切片厚度略高于透射深度时，层间结合紧密，二次曝光效果不明显，有利于提高成形精度并抑制层间应力。高温烧结阶段，随着烧结助剂Al2O3和Y2O3形成共晶液相数量增加，相转变与致密化进程增强，孔隙数量显著降低，Si3N4陶瓷的抗弯强度增大；然而，当烧结助剂过量时，共晶液相分布于Si3N4晶界，降低抗弯强度，相对密度呈现相同的规律。最终，通过光固化成形参数优化与烧结助剂调控，Si3N4陶瓷获得84%~85%的相对密度以及140MPa~149 MPa的抗弯强度。本项目建立了高性能多孔夹层Si3N4陶瓷制造方法，为高马赫数飞行器天线罩的结构设计优化与精密制造提供创新的思路，加速我国高马赫数飞行器的发展。