硅溶胶强化辅助制备C纤维增韧氧化铝结合莫来石陶瓷基复合材料

Preparation of C fiber reinforced alumina-mullite composite assisted by silica sol infiltration

通过氧化铝先驱体溶液循环浸渍热解结合硅溶胶浸渗强化的方法制备了三维C纤维预制体增韧的氧化铝结合莫来石陶瓷基复合材料 ,研究了氧化铝浸渗工艺对试样增重率、气孔率以及热处理温度对试样内气孔尺寸和分布的影响 ,分析了复合材料物相、微结构以及复合材料的力学性能。结果表明 ,硝酸铝饱和溶液浸渗纤维预制体并热解后试样的增重率和开气孔率呈类似抛物线曲线 ;由于硝酸铝分解生成氧化铝的煅烧温度不同 ,氧化铝晶态及物理特性不同 ,试样内气孔尺寸和分布差别较大 ;选择经过 115 0℃预处理的试样进行硅溶胶浸渗 ,然后 14 0 0℃处理 2h ,氧化硅与氧化铝完全反应生成莫来石 ,获得了较为致密的复合材料 ,室温三点弯曲强度和断裂应变分别为 180MPa和 2 .2 %。

3D C fiber preform reinforced alumina-mullite composite was manufactured. The materials was produced by precursor infiltration and pyrolysis and subsequently strengthened by silica sol infiltration route after coating the fiber preform with a 0.2μm thick carbon layer by chemical vapor infiltration. The composite was manufactured by infiltrating the preform with aluminium nitrate saturation sol, drying in an autoclave and subsequently heat treating at 950°C and pyrolysis of the aluminium nitrate. After ten cycles, the specimen was polished to remove the alumina matrix on the surface of the specimen, which generate 'bottle effect' and prevent aluminium nitrate saturation sol from entering into the specimen. After another four cycles like above, the specimen was heated to 1150°C and 1300°C in Ar to transfer the amorphous alumina to γ-Al2,O3 and 2.2% α-Al2O3. The pore size and distribution in the specimens heat-treated in different temperature was determined. The specimen, which was heat-treated at 1150°C, was dipped in silica sol in vacuum condition, then drying in 100°C. Then the specimen containing silica was heated to 1400°C for 2h in Ar to impel the reaction between γ-Al2O3 and silica to create mullite. The stick-like mullite was observed which make for the strength of the composite. At the same time, the micro-cracks were observed on the unpolished cross-section matrix of composite, which was defected around the C fiber and doesn't damage the C fiber. It indicated the C interface was a weak interphase between the C fiber and alumina matrix. The three-point flexural strength and the strain of the as-fabricated composite were 180MPa and 2.2%.