Effect of powdered h-BN as addition on the microstructure and mechanical properties of C/C composites fabricated by chemical vapor infiltration

In current work, h-BN powders were introduced into carbon fiber needle felt via powder addition in order to prepare chemical vapor infiltration (CVI) based C/C-BN composites. The microstructures and mechanical properties of as-prepared carbon/carbon (C/C) with 9 vol% of h-BN (C/C-BN9) were investigated in comparison to the pure C/C composites with same fiber architecture. The results indicated that the pyrolytic carbon (PyC) with higher degree of texture caused by h-BN in C/C-BN9 composites enhanced the interfacial bonding of PyC/fiber. Moreover, compared to C/C composites, the addition of h-BN resulted in smaller-sized PyC, leading to less and narrower microcracks in matrix. After introduction of h-BN into matrix, the flexural strength remained almost the same, while decreased impact toughness and more brittle fracture behavior were achieved in C/C-BN9 composites. However, the h-BN powders as addition could result in significantly enhanced compressive strength with higher isotropic stress-strain response in both vertical and parallel directions.