Preparation of three-dimensional braided carbon fiber reinforced
mullite composites from a sol with high solid content
Wei ZHANG1,2,Qing-song MA2,Ke-wei DAI2,Wei-guo MAO1
1.School of Materials Science and Engineering,Xiangtan University,Xiangtan411105,China;
2.Science and Technology on Advanced Ceramic Fibers&Composites Laboratory,
National University of Defense Technology,Changsha410073,China
Abstract:To prepare the three-dimensional braided carbon fiber reinforced mullite(3D C/mullite)composites,an Al2O3−SiO2sol with a solid content of20%(mass fraction)and an Al2O3/SiO2mass ratio of2:1was selected as the raw material.Characteristics and mullitization of the sol were analyzed throughly.It is found that the formation of mullite is basically completed at1300︒C and the gel powders exhibit favorable sintering shrinkage.The3D C/mullite composites without interfacial coating were fabricated through the route of vacuum impregnation−drying−heat treatment.Satisfied mechanical properties with a flexural strength of241.2MPa and a fracture toughness of10.9MPa∙m1/2are obtained although the total porosity reaches26.0%.Oxidation resistances of the composites at1200,1400and1600︒C were investigated.Due to the further densification of matrix,the3D C/mullite composites show tiny mass loss and their mechanical properties are well retained after oxidation at1600︒C for30min.
Key words:carbon fiber reinforced mullite composites;Al2O3−SiO2sol;mechanical properties;oxidation resistance
Mullite ceramics are well known as the high performance structural materials owing to their low density,low thermal expansion,desirable thermal stability,excellent oxidation resistance,and so on[1−4]. However,the wide applications of monolithic mullite ceramics are restricted because of their low fracture toughness(2−3MPa∙m1/2).Of all the toughening methods,continuous fiber reinforcement is predominant because of its outstanding damage tolerance.So far, oxide fiber,SiC fiber and C fiber have been employed to reinforce mullite ceramics[5−11]and the oxide fibers are the most extensively used reinforcement.
Although carbon fiber has been extensively used to reinforce other ceramics,the study on the carbon fiber reinforced mullite composites has been rarely reported[10,11].In the studies of WU et al[10,11], unidirectional(UD)carbon fiber tow was impregnated in a single stage by passing it through an Al2O3−SiO2sol and wound onto a hexagonal drum to form a sheet prepreg.After being dried,the prepregs were stacked and hot-pressed to obtain the UD C/mullite composites.The resulted composites showed high mechanical properties in X direction.However,the interlaminar strength and the in-plane strength were low due to the absence of carbon fiber in the Y and Z directions.Furthermore,this route is difficult for the fabrication of large-size parts with a complex shape.
Three-dimensional(3D)braided fiber preform is considered as a desirable reinforcement for high performance composite materials because of its flexibility in the structure design,desirable comprehensive performance and adaptability to the complex shape.In order to realize the homogeneous distribution of matrix and the low fabrication temperature,gas infiltration and solution impregnation routes are preferentially adopted to fabricate3D fiber reinforced mullite composites,especially the large-size complex parts.Nevertheless,proper gaseous raw materials for Al2O3−SiO2co-deposition have not been
Foundation item:Project(SAST2015043)supported by the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology,China;
Project(614291102010117)supported by the Open Foundation of Science and Technology on Thermostructural Composite Materials
Laboratory,China;Project(11572277)supported by the National Natural Science Foundation of China
Corresponding author:Qing-song MA,Tel:+86-731-84573168,Fax:+86-731-84576578,E-mail:nudtmqs1975@http://m.wendangku.net/doc/9da45ef62379168884868762caaedd3382c4b53c.html ;