为了研究不同碳纤维原丝数量对C/C-SiC复合材料抗冲击性能的影响,采用两步化学气相渗透法(CVI)对不同碳纤维原丝数量(K)的2.5D碳纤维针刺预制体进行陶瓷基体致密化,得到2种C/C-SiC复合材料(3K-C/C-SiC和12K-C/C-SiC)。采用体积法和压汞仪测定了2种C/C-SiC复合材料的密度和开孔孔隙率。通过X射线衍射、扫描电子显微镜、能谱(EDS)分析等表征手段对C/C-SiC复合材料的结构和形貌进行表征。结果表明,碳纤维原丝数量对C/C-SiC复合材料的结构与性能均有较大影响。采用两步CVI工艺制备的C/C-SiC复合材料,热解碳(PyC)和碳化硅(SiC)都能均匀沉积在2种碳纤维表面,3K,12K碳纤维2.5D针刺预制体增重分别约30%和25%,3K-C/C-SiC和12K-C/C-SiC复合材料的密度分别约为0.89,0.74 g/cm3,开孔孔隙率分别约为52.87%和56.53%,是由于3K碳纤维2.5D针刺预制体的纤维含量低,密度小,孔隙率大,沉积在纤维表面的PyC和SiC更多,同时SiC的密度大于C的密度,从而使得3K-C/C-SiC复合材料的密度较大,孔隙率较小。通过对2种C/C-SiC复合材料的结构和形貌进行表征发现3K-C/C-SiC,12K-C/C-SiC复合材料中SiC含量分别约为27.2%和11.1%,C含量分别约为72.8%和88.9%,单根纤维束中PyC层厚度分别约为2.162,2.145 μm,SiC层分别约为1.890,1.284 μm;3K-C/C-SiC复合材料SiC含量更高、C含量较低,这是由于3K碳纤维2.5D针刺预制体的碳纤维含量较低,孔隙率较大,从而能使更多的PyC和SiC沉积在碳纤维表面。经抗冲击测试测得到3K-C/C-SiC和12K-C/C-SiC复合材料的冲击韧性分别约为25.624,14.310 kJ/m2,吸收功分别约为1.52 J和1.09 J。通过摆锤式冲击试验结果发现,3K-C/C-SiC复合材料的抗冲击性能要优于12K-C/C-SiC复合材料,其优良的抗冲击性能主要是因为3K-C/C-SiC复合材料表面的SiC层更厚,使其断裂需要更多的断裂功,PyC具有良好的韧性,能够提高纤维的抗冲击性能,同时3K碳纤维预制体的韧性要优于12K碳纤维预制体,因此断裂3K-C/C-SiC中的纤维束需要更多的断裂功。
In order to investigate the effect of different counts of carbon fiber protofilaments on the impact resistance of C/C-SiC composites, two types of C/C-SiC composites (3K-C/C-SiC and 12K-C/C-SiC) were produced through the ceramic substrate densification of 2.5D carbon fiber needled preforms with different counts of carbon fiber protofilaments (K) via a two-step chemical vapor infiltration (CVI) method. The density and open porosity of two kinds of C/C-SiC omposites were determined by the volumetric method and mercury porosimeter. The structure and morphology of C/C-SiC composites were characterized through characterization methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). Results showed that the counts of carbon fiber protofilaments were found to have a significant impact on the structure and properties of C/C-SiC composites. Pyrolytic carbon (PyC) and SiC were uniformly deposited on the surfaces of two kinds of carbon fibers for C/C-SiC composites prepared by two-step CVI. The weight gain for the 3K carbon fiber 2.5D needled preform was approximately 30%, while it was about 25% for the 12K carbon fiber 2.5D needled preform. The 3K-C/C-SiC composites had a density of approximately 0.89 g/cm3 and an open porosity of about 52.87%. The 12K-C/C-SiC composites had a density of approximately 0.74 g/cm3 and an open porosity of about 56.53%. These differences were attributed to the lower fiber content, lower density, and greater porosity of the 3K carbon fiber 2.5D needled preform, which facilitated greater deposition of PyC and SiC on the surfaces of fibers. At the same time, the density of SiC was greater than that of C, resulting in a higher density and lower porosity of 3K-C/C-SiC composites. By characterizing the structure and morphology of two types of C/C-SiC composites, it was found that the SiC contents in 3K-C/C-SiC and 12K-C/C-SiC composites were about 27.2% and 11.1%, respectively, and the C contents were about 72.8% and 88.9%, respectively. The thicknesses of PyC layer in a single fiber bundle were about 2.162 and 2.145 μm, respectively. The thicknesses of SiC layers were approximately 1.890 and 1.284 μm, respectively. 3K-C/C-SiC composite material had a higher SiC content and lower C content. This was due to the lower carbon fiber content and higher porosity of the 3K carbon fiber 2.5D needle preform, which could cause more PyC and SiC to deposit on the surfaces of the carbon fibers. Through the impact resistance test, it was determined that the impact toughness of 3K-C/C-SiC and 12K-C/C-SiC composites was approximately 25.624 kJ/m2 and 14.310 kJ/m2, respectively, with absorbed energy values of about 1.52 J and 1.09 J, respectively. Results of pendulum impact tests showed that the 3K-C/C-SiC composites had superior impact resistance compared to the 12K-C/C-SiC composites. This enhanced impact resistance was mainly due to the thicker SiC layer on the surface of 3K-C/C-SiC composites, which required more fracture work, and PyC possessed excellent toughness, which enhanced the fibers’ impact resistance. Furthermore, the toughness of the 3K carbon fiber preform was superior to that of the 12K carbon fiber preform. As a result, fracturing the fiber bundles in the 3K-C/C-SiC required more fracture work.
