Fabrication And Characterization Of 3D Woven Carbon Fiber/Ceramic Matrix Composites

Fiber reinforced ceramic matrix composites (CMC) possess advantages including lower density, better toughness and higher specific strength than monolithic ceramic materials. Therefore, fiber reinforced CMC are being widely used in high performance applications such as turbine engines and high-grade refractory. Numerous studies have been conducted on fiber and whisker reinforced ceramic compositesRecently,3D textile structure reinforced ceramics are the better choice compared with fiber/whisker and 2D structure reinforced composites including better delamination resistance and higher toughness. The main processing routes for 3D structure reinforced ceramic composites are chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP). In CVI routes, the ceramic matrix is deposited into the pores of the fibrous preform through chemical vapor reaction to densify the ceramic composites. However, CVI processes require a relatively long densification time as well as complex facilities which makes it high energy consumption and expensive, and the products often exhibit residual porosity. In PIP process, the fibrous preform is firstly impregnated with a liquid precursor of the matrix, and then pyrolyzed by curing and chemical reaction. The limitations of this process are long processing time and high labor cost during the repeating impregnation-pyrolysis cycles. In addition, PIP may not work for 3D preforms since it is often difficult to infiltrate the preform with enough precursors especially when the precursor is in a form of particles suspended in a liquid, leaving substantial amount of pores in the composite. In this paper, A new modified slurry impregnation and hot pressing method (SIHP) was adopted to fabricate a new type of 3D woven carbon fiber/silica ceramic matrix composites (3D Cf/SiO2 CMC). At the same time, MWCNTs were successfully introduced into the composites, which increased toughness of the composites further. First the preform was fully infiltrated silica slurry, after drying in the oven, impregnated with silica slurry using vacuum assisted slurry transfer molding (VASTM), which helps to increase density of the composites. The mechanical properties, microstructure and toughing mechanism of the composites were investigated by three-point bending test, impact test and scanning electron microscopy. The 3D Cf/SiO2 CMC showed a higher flexural strength than that of pure SiO2 such as the flexual strengh in both warp and weft direction is 66.87Mpa and 102.33Mpa as well as 71.43Gpa elastic modulus. At the same time,the mechanical properties in weft direction is better than that of warp one because the volume fraction of weft yarn is 3 times as much as warp yarn. In impact test, the composite fails at a non-brittle mode due to the fiber debonding, pullout effects, and a layer by layer failure process of the 3D structure and thus absorbs substantially more energy than that of pure SiO2.Compared with 0.05wt%CNTs-Cf/SiO2 composites, the one with 0.5wt%CNTs showed higher flexural strength(140%) and elastic modulus(130%). Also they showed the higher absorbed every in impact testing (warp 0.341J,weftl.127J) while the one with 0.05wt%CNTs (warp0.247J,weft0.789J).In addition,3D Cf/ZrO2 CMC were also studied and the fabrication methods were similar to that of 3D Cf/SiO2 CMC. To some extent, microcraks were cured when MWCNTs were introduced into this composites. So it is valuble to study the relationship between the amount of CNTs and the quality of the zirconia composites.