多孔Si3N4与透明AlON陶瓷连接用Al2O3缓冲层的仿生构筑及其应力缓解机制研究

The development of high-temperature-resistant microwave/ infrared dual-mode radome is of great significance to improve the level of high-speed and long-distance precise guidance weapon in our country. Because no single material could be used as dual mode radome for high- speed flight, the joining of porous Si3N4 ceramic to transparent AlON ceramic as microwave/infrared dual mode radome is an important way. However, due to the mismatch of thermal expansion coefficient between porous Si3N4 ceramic and transparent AlON ceramic, cracks will appear in the matrix of transparent AlON ceramic under thermal residual stress, resulting in the failure of joining. Due to the advantages such as high melting point, high strength, low dielectric constant and suitable thermal expansion coefficient, porous Al2O3 ceramic is an ideal buffer layer material for the joining of porous Si3N4 ceramic to transparent AlON ceramic. In this project, the porous Al2O3 buffer layer will be constructed by freeze casting with dual temperature gradients to obtain biomimetic pore structure based on the finite element numerical simulation, which is beneficial for releasing residual stress and improving the strength of joint. Nano Si3N4 will be used instead of submicron Si3N4 to modify oxynitride glass solder and the crystallization mechanism will be investigated to promote the crystallization then further improve the strength of joint. The interface structure, interfacial reaction mechanism, fracture mode of joint and stress distribution rule will be analyzed to elucidate the residual stress releasing mechanism of using porous Al2O3 ceramic as buffer layer. This project will provide technical support and theoretical basis for the development of microwave/infrared dual mode radome.

研制耐高温微波/红外复合天线罩对于提升我国高速远程精确制导武器水平具有重要意义。由于没有一种材料能同时满足高速飞行和微波/红外双重透过性要求，将多孔Si3N4和透明AlON天线罩连接是研制微波/红外复合天线罩的重要途径。但多孔Si3N4和透明AlON陶瓷热膨胀系数不匹配，连接过程中的残余应力将导致透明AlON陶瓷开裂，使得连接失败。多孔Al2O3陶瓷耐高温、强度高、介电常数小、热膨胀系数适中，是连接多孔Si3N4与透明AlON陶瓷的理想缓冲层材料。本项目拟基于有限元数值模拟，采用双向冰冻法仿生构筑合适厚度和孔隙率的多孔Al2O3陶瓷缓冲层，缓解残余应力的同时提高缓冲层的强韧性。以纳米Si3N4改性的氧氮玻璃为焊料并研究其晶化机制来协同提升接头性能。分析连接界面结构、界面反应机制及接头断裂模式和应力分布规律，阐明应力缓解机制。本项目的开展将为微波/红外复合天线罩的研制提供技术支撑和理论基础。

研制耐高温微波/红外双模天线罩对于提升我国高速远程精确制导武器水平具有重要意义。由于没有一种材料能同时满足高速飞行和微波/红外双重透过性要求，将多孔Si3N4和透明AlON天线罩连接是研制微波/红外双模天线罩的重要途径。但多孔Si3N4和透明AlON陶瓷热膨胀系数不匹配，连接过程中的残余应力将导致透明AlON陶瓷开裂，使得连接失败。多孔Al2O3陶瓷耐高温、强度高、介电常数小、热膨胀系数适中，是连接多孔Si3N4与透明AlON陶瓷的理想缓冲层材料。基于此设想，本项目首先采用有限元数值模拟发现，通过氧氮玻璃热膨胀系数设计，可使透明AlON陶瓷一侧的热应力在可容忍的范围内，避免开裂，当焊料的热膨胀系数为8×10-6·K-1时，多孔Si3N4、透明AlON陶瓷和氧氮玻璃侧的热应力都在250MPa附近，具备实现两者有效连接的可能性；通过双向冷冻法，构筑出具有再生花植物杆孔道微结构特征的多孔Al2O3陶瓷，在传统直通孔结构的基础上，增加了横向的网络支撑，当浆料固含量为30vol%时，层与层之间的间隙更小，有助于增强横向的力学性能，从而增强缓冲层的连接强度，并且通过有限元模拟计算得出当多孔Al2O3陶瓷缓冲层厚度为3mm，透明AlON陶瓷一侧的最大热应力约为100 MPa，低于透明AlON陶瓷弯曲强度平均值的50%，选此厚度制备缓冲层具有较好的应力容忍性；通过氧氮玻璃组分设计，制备出多种组分、具有热膨胀系数梯度的氧氮玻璃，并对其析晶行为进行研究，通过合理的析晶处理（1200℃/10min），可提高力学性能；通过微晶化氧氮玻璃与双向孔结构多孔Al2O3陶瓷缓冲层联用，本项目在1500℃，N2气氛下热处理15分钟，并在1200℃进行晶化处理，有效缓解多孔Si3N4与透明AlON陶瓷之间的热应力，并且增强接头强度，获得可靠的连接接头。本项目的实施可以为热膨胀系数迥异的异质陶瓷连接提供启示。