化学气相渗透法制备2维和2.5维C/SiC复合材料及其拉伸性能

采用化学气相渗透法制备了2维和2.5维碳纤维增强碳化硅(carbon-fiber-reinforced silicon carbide,C/SiC)复合材料,沿经纱(纵向)和纬纱(横向) 2个方向对2种复合材料进行了室温拉伸性能测试,并从预制体结构和原始缺陷分布的角度对比分析了两者力学性能之间的差异.结果表明:两种C/SiC复合材料均表现出明显的非线性力学行为,在经纱方向和纬纱方向上,2维C/SiC复合材料力学性能表现为各向同性,而2.5维C/SiC复合材料力学性能则表现出明显的各向异性:经纱方向上2.5维C/SiC复合材料的拉伸强度和拉伸模量(326 MPa,153 GPa)均高于2维C/SiC复合材料的(245 MPa,96 GPa),纬纱方向上的(145 MPa,62 GPa)均低于2维C/SiC复合材料的(239 MPa,90 GPa).两种复合材料的拉伸断裂行为均表现为典型的韧性断裂,并伴有大量的纤维拔出.两种复合材料中纱线断裂均呈现出多级台阶式断裂方式,但其断裂位置并不相同.2.5维C/SiC复合材料中由于经纱路径近似于正弦波,弯曲程度较大,在纱线交叉点处造成明显的应力集中,因此经纱多在纱线交叉点处断裂;而纬纱由于其路径近乎直线,应力集中现象不明显,因此纬纱断裂位置呈随机分布.2维C/SiC复合材料中经纱和纬纱由于其路径类似于2.5维C/SiC复合材料中的经纱,因此其断裂位置也多在纱线交叉点处.微观结构观察表明不同的编织结构是造成两种复合材料在不同方向上力学性能差异的主要原因.

TENSILE BEHAVIOR OF 2 D AND 2.5 D C/SiC COMPOSITES FABRICATED BY CHEMICAL VAPOR INFILTRATION

Two-dimensional (2 D) and two-and-a-half-dimensional (2.5 D) carbon-fiber-reinforced silicon carbide (C/SiC) composites were prepared by the chemical vapor infiltration process and the tensile properties of the composites along the warp and weft directions were compared as a function of fiber architectures and processing-induced cracks. The results show that both the composites exhibit mostly nonlinear mechanical behavior. However, the 2.5 D C/SiC composite is highly anisotropic, while the 2 D C/SiC composite is near isotropic with respect to the warp and weft directions. The 2.5 D C/SiC composite shows higher tensile strength and modulus than the 2 D C/SiC composite in the warp direction (326 MPa, 153 GPa vs. 245 MPa, 96 GPa), but lower strength and modulus than the 2 D C/SiC composite in the weft direction (145 MPa, 62 GPa vs. 239 MPa, 90 GPa). Both of the composites show a noncatastrophic failure mode accompanied with substantial fiber pullout. The fracture of yarns in both the composites demonstrates multi-step fiber fracture, but with different fracture locations. The large undulation angle of the warp yarns in the 2.5 D C/SiC composite due to its sinusoidal path causes stress concentration in the yarn crossover point, where the warp yarns are consequently most likely to occur. In contrast, the weft yarns have approximately straight paths and then fracture at random locations due to the absence of stress concentration. As for the 2 D C/SiC composite, both the warp and weft yarns in it have similar paths to those of the warp yarns in the 2.5 D C/SiC composite; therefore, they fracture in the same manner as do the warp yarns in the 2.5 D C/SiC composite. Microstructural observations reveal that it is the characteristics of the weave architectures that cause the differences in mechanical properties between the two kinds of composites.