本文選題：冷噴涂 + 氮化硅陶瓷�。� 參考：《武漢理工大學》2015年碩士論文

【摘要】：隨著航空航天技術(shù)與現(xiàn)代科學技術(shù)的快速發(fā)展,對透波材料性能要求不斷提高,要求材料具有較好的力學性能、較低的熱導率和超寬頻帶范圍內(nèi)高的透波率。由于氮化硅(Si3N4)陶瓷是結(jié)構(gòu)陶瓷中綜合性能最好的材料之一,其作為透波材料已受到國內(nèi)外學者的重視。本文針對透波材料高強度高透波率的要求,提出了具有孔隙梯度結(jié)構(gòu)的陶瓷基透波材料。本文首次將先進的冷噴涂成型技術(shù)與低成本的無壓燒結(jié)技術(shù)有機結(jié)合制備了具有孔隙梯度結(jié)構(gòu)的Si3N4陶瓷透波材料。首先,制備了高孔隙率的Si3N4多孔陶瓷。采用無壓燒結(jié)技術(shù)于1300℃氮氣氣氛下,制備了低介電常數(shù)的氮化硅納米線(SNNWs)增強的Si3N4多孔陶瓷,研究了SNNWs含量對孔隙率、力學性能和介電性能的影響及增強機制。結(jié)果表明:材料的孔壁及淀粉燃盡形成的孔隙內(nèi)產(chǎn)生了長度50nm且直徑2.5~10nm的SNNWs;材料的孔隙率50~55%,抗彎強度19MPa~39MPa,介電常數(shù)2.9~3.3,隨SNNWs含量的增加,抗彎強度先急劇增加后減小,而孔隙率和介電常數(shù)分別緩慢減少和增加;SNNWs增強的Si3N4多孔陶瓷的增強機制為拔出效應及能量吸收效應。其次,制備了系列不同孔隙率且厚度及孔隙率可控的Si3N4陶瓷涂層。先制備了低粘度和高固相量的Si3N4漿料,以MgO-Al2O3-SiO2作為燒結(jié)助劑,再采用噴涂漿料的冷噴涂成型及無壓燒結(jié)制備了厚度及孔隙率可控的Si3N4陶瓷涂層,研究了燒結(jié)助劑含量和冷噴涂工藝參數(shù)(噴涂壓力、噴涂距離和噴涂時間)對涂層表面形貌、微觀結(jié)構(gòu)、厚度和孔隙率的影響及結(jié)合強度。結(jié)果表明:當Si3N4漿料中pH值8、分散劑0.6wt.%和固相量40wt.%時,其粘度為41mPa·s且分散性及穩(wěn)定性好,適用于冷噴涂;最佳冷噴涂工藝參數(shù)為噴涂壓力0.8MPa和噴涂距離12cm;通過調(diào)控燒結(jié)助劑含量和冷噴涂工藝參數(shù),制備了孔隙率5~33%,厚度5~428μm和結(jié)合強度12~58MPa的Si3N4陶瓷涂層,結(jié)合強度隨著涂層厚度的增加而減小,涂層與基體結(jié)合良好且界面處無裂紋。最后,采用微波傳輸線理論結(jié)合四端網(wǎng)絡結(jié)構(gòu)算法計算了孔隙梯度透波材料的透波率,對其結(jié)構(gòu)進行了優(yōu)化設計,優(yōu)化設計結(jié)果表明當層數(shù)n=4,總厚度d=2.4mm,層厚比d1:d涂層=5:3,最內(nèi)外層介電常數(shù)分別為ε1=3和εn=6時,具有孔隙梯度結(jié)構(gòu)的Si3N4陶瓷透波材料的透波率在0.5~40GHz超頻帶范圍內(nèi)70%,滿足高透波要求;根據(jù)優(yōu)化設計結(jié)果采用冷噴涂成型與無壓燒結(jié)制備了具有孔隙梯度結(jié)構(gòu)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，

本文編號：2016125