孔隙梯度结构氮化硅陶瓷的冷喷涂成型、无压烧结及其性能研究

发布时间：2018-06-14 00:10

  本文选题：冷喷涂 + 氮化硅陶瓷　； 参考：《武汉理工大学》2015年硕士论文

【摘要】：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范围内高的透波率。由于氮化硅(Si3N4)陶瓷是结构陶瓷中综合性能最好的材料之一,其作为透波材料已受到国内外学者的重视。本文针对透波材料高强度高透波率的要求,提出了具有孔隙梯度结构的陶瓷基透波材料。本文首次将先进的冷喷涂成型技术与低成本的无压烧结技术有机结合制备了具有孔隙梯度结构的Si3N4陶瓷透波材料。首先,制备了高孔隙率的Si3N4多孔陶瓷。采用无压烧结技术于1300℃氮气气氛下,制备了低介电常数的氮化硅纳米线(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。结果表明:材料的孔壁及淀粉燃尽形成的孔隙内产生了长度50nm且直径2.5~10nm的SNNWs;材料的孔隙率50~55%,抗弯强度19MPa~39MPa,介电常数2.9~3.3,随SNNWs含量的增加,抗弯强度先急剧增加后减小,而孔隙率和介电常数分别缓慢减少和增加;SNNWs增强的Si3N4多孔陶瓷的增强机制为拔出效应及能量吸收效应。其次,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。先制备了低粘度和高固相量的Si3N4浆料,以MgO-Al2O3-SiO2作为烧结助剂,再采用喷涂浆料的冷喷涂成型及无压烧结制备了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(喷涂压力、喷涂距离和喷涂时间)对涂层表面形貌、微观结构、厚度和孔隙率的影响及结合强度。结果表明:当Si3N4浆料中pH值8、分散剂0.6wt.%和固相量40wt.%时,其粘度为41mPa·s且分散性及稳定性好,适用于冷喷涂;最佳冷喷涂工艺参数为喷涂压力0.8MPa和喷涂距离12cm;通过调控烧结助剂含量和冷喷涂工艺参数,制备了孔隙率5~33%,厚度5~428μm和结合强度12~58MPa的Si3N4陶瓷涂层,结合强度随着涂层厚度的增加而减小,涂层与基体结合良好且界面处无裂纹。最后,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;根据优化设计结果采用冷喷涂成型与无压烧结制备了具有孔隙梯度结构Si3N4陶瓷透波材料。
[Abstract]:With the rapid development of aeronautics and space technology and modern science and technology, the requirements for the properties of wave-permeable materials are constantly improved, requiring better mechanical properties, lower thermal conductivity and high transmittance in the ultra-wide band. As silicon nitride Si _ 3N _ 4) ceramic is one of the best composite materials in structural ceramics, it has been paid attention to as a wave-permeable material at home and abroad. In order to meet the requirement of high strength and high transmittance of wave-permeable materials, a ceramic based wave-permeable material with porous gradient structure is proposed in this paper. In this paper, the advanced cold spray molding technology and low cost pressureless sintering technology were used to fabricate Si _ 3N _ 4 ceramic wave permeable materials with porous gradient structure for the first time. Firstly, Si _ 3N _ 4 porous ceramics with high porosity were prepared. Si3N4 porous ceramics reinforced by silicon nitride nanowires with low dielectric constant were prepared by pressureless sintering at 1300 鈩，

本文编号：2016125