具有孔隙梯度结构的陶瓷基复合材料的研制及其宽频带高透波率机理研究

Aiming at the majoy difficulties of broadband electromagnetic wave penetration materials in structural design and optimization, materials complete preparation and microstructure control, the current project is going to build the physical and geometrical models for porous graded structure, to setup the correlation between the broadband high transmittance and the graded dielectric constant for the wave penetration materials, to clear the broadband high transmittance mechanism, to develop the porous graded structural design and optimization technique for ultra-broadband and high transmittance ceramic matrix materials; and then to study the preparation of phosphate bonded silicon nitride (Si3N4) porous ceramics with controlled porous structure, dielectric properties and high strength, and Si3N4 ceramics with porous graded structure by cold spraying and heating processes, to test and evaluate the mechanical, thermal, dielectric properties together with electromagnetic wave transmittance for Si3N4 matrix ceramics with porous graded structure, to modify the structural design and processing parameters, finally to achieve the Si3N4 electromagnetic wave penetration ceramics with porous graded structure, which have ultra-broadband and high transmittance properties. The predicted achievements of the project will supply theoretical design and preparation technique for high temperature resistance, high strength and broadband high transmittance "structure-function integration" electromagnetic wave penetration materials applied in the aerospace field.

针对宽频带陶瓷基透波材料在结构设计与优化、整体制备与结构控制方面的瓶颈技术问题，本项目旨在通过构筑梯度结构的物理与几何模型，建立透波材料的宽频带高透波率与其介电常数梯度变化的物理关联，揭示透波材料宽频带高透波率机理，发展满足宽频带高透波率要求的陶瓷基复合材料的孔隙梯度结构设计与优化技术；研究孔隙结构可控、介电性能可控、高强度的磷酸盐结合氮化硅多孔陶瓷和具有孔隙梯度结构的氮化硅基陶瓷的冷喷涂及热处理制备技术；对氮化硅基陶瓷透波材料进行力学性能、热学性能、介电性能、透波率等综合测试与评价，修正设计与工艺参数，研制出综合性能优异的满足宽频带高透波率设计要求的具有孔隙梯度结构的氮化硅基陶瓷透波材料。项目预期成果将为航空航天领域中的耐高温、承载、宽频带高透波的"结构-功能一体化"透波材料提供理论设计和制备技术的参考。

随着航空航天技术与现代科学技术的快速发展，对透波材料性能要求不断提高，要求材料具有较好的力学性能、较低的热导率和超宽频带高透波率。针对宽频带陶瓷基透波材料在结构设计与优化、整体制备与结构控制方面的瓶颈技术问题，本项目旨在通过构筑具有梯度结构的陶瓷基复合材料的物理与几何模型，建立该特种结构透波材料的宽频带透波率与其介电常数梯度变化的物理关联，发展满足宽频带高透波率要求的陶瓷基复合材料的孔隙梯度结构设计与优化技术，研制综合性能优异的满足宽频带高透波率要求的具有孔隙梯度结构的氮化硅基陶瓷透波材料。首先，采用微波传输线理论结合四端网络结构算法计算了孔隙梯度透波材料的透波率，对其结构进行了优化设计，优化设计结果表明当层数n=4，总厚度d=2.4mm，层厚比d1：d涂层=5：3，最内外层介电常数分别为ε1=3和εn=6时，具有孔隙梯度结构的Si3N4陶瓷透波材料的透波率在0.5～40GHz超频带范围内>70％，满足高透波要求。其次，采用无压烧结技术于1300℃氮气气氛下制备了低介电常数的SNNWs增强的Si3N4多孔陶瓷，研究了SNNWs含量对孔隙率、力学性能和介电性能的影响及增强机制。第三，采用冷喷涂成型和无压烧结技术制备了系列不同孔隙率且厚度及孔隙率可控的Si3N4陶瓷涂层，研究了烧结助剂含量和冷喷涂工艺参数对涂层表面形貌、微观结构、厚度和孔隙率的影响，获得了孔隙率可控的氮化硅多孔陶瓷涂层的制备技术及孔隙结构控制方法。最后，根据宽频带高透波率要求的陶瓷基复合材料的孔隙梯度结构的最佳设计结果，选择符合最佳设计结果的多孔Si3N4陶瓷涂层，制备了介电常数从内到外按3.1～6.0梯度变化、透波率在0.5～40GHz的测试频率范围内均大于70%的具有孔隙梯度结构Si3N4陶瓷透波材料。