Structural Design and processing of Laminated Fiber-reinforced Ceramic Matrix Composites

采用溶胶-凝胶法制备了莫来石粉体和Si-Ti-C-O纤维编织物，并采用过滤法或刮刀法制备了莫来石/Si-Ti-C-O纤维复合材料。将含6和10体积%织物的层压绿色复合材料在39 MPa的压力下在1500 ℃-1650 ℃下在N2气氛中热压1 h至接近全密度。经1650 ℃热压处理后，在纤维与基体的界面处形成约10 nm厚的石墨层和0.1-0.2 μ m的TiC颗粒，纤维中存在10-30 nm的β-SiC和TiC颗粒以及短周期结构的石墨相。结果表明，纤维的晶化过程伴随着纤维中非晶相的形成而进行。纤维的EDS定量分析表明，在1650 ℃热压过程中，当氧含量为13.7%时，纤维发生了热解。在Si-Ti-C-O纤维含量为10-30 vol%，热压温度为1650 ℃的复合材料中，单块莫来石的断裂行为由应力-位移线性关系转变为非线性关系。O织物使莫来石的四点弯曲强度（328 MPa）在织物体积分数为6%时降低到292 MPa，在织物体积分数为10%时降低到271 MPa，在织物体积分数为20- 30%时降低到59-78 MPa。复合材料弯曲强度的降低是由于沿复合材料长度方向沿着莫来石层间产生的残余拉应力所致。研究复合材料在多轴应力状态下的断裂行为对实际应用中的结构件具有重要意义。复合材料的拉压双向强度低于莫来石陶瓷。

A sol-gel-processed mullite powder and Si-Ti-C-O fiber woven fabrics were formed into laminated composites by filtration or doctor blade method using aqueous mullite suspensions containing polyacrylic ammonium and methyl cellulose at pH 8.5. The laminate green composites with 6 and 10 vol% fabrics were hot-pressed to near full density at 1500ﾟ-1650ﾟC for 1h under a pressure of 39 MPa in a N2 atmosphere. Graphite layrs of about 10 nm thickness and TiC particles of 0.1-0.2 mum were produced at the interfaces between fibers and matrix after hot-pressing at 1650ﾟC.beta-SiC and TiC particles of 10-30 nm and graphite phase with short cycle structure were recognized in the fibers. These results indicate that the crystallization of fibers progresses with formation of the amorphous phase in fiber. The EDS quantification of the fibers indicated that the fibers pyrolyzed during hot-pressing at 1650ﾟC by 13.7 % of oxygen content.A linear relation of stress-displacement in fracture behavior of monolithic mullite changed to a non-linear relation in the composites with 10-30 vol% of Si-Ti-C-O fabrics and hot-pressed at 1650ﾟC.Addition of Si-Ti-C-O fabrics decreased the four point flexural strength of monolithic mullite (328 MPa) to 292 MPa at 6 vol%, 271 MPa at 10 vol% and 59-78 MPa at 20-30 vol% of fabrice. The decrease of flexural strength for the composite was due to the residual tensile stress caused in the mullite layrs along the direction of length of composites. It is important to study fracture behavior of composite under multiaxial stress state for structural components in practical applications. The tension-compression biaxial strengh of composite materials was lower than that of monolithic mullite ceramics.