Microstructures and mechanical behaviors of CVI-based C/C composites containing h-BN powdered additives

Abstract Hexagonal boron nitride (h-BN) powders were introduced into carbon fiber preform by powder addition and subsequent combined with chemical vapor infiltration (CVI) for densification to prepare carbon fiber reinforced/carbon and boron nitride dual matrix composites (C/C-BN). Microstructures and mechanical properties of C/C composites with three different volume contents of h-BN powders were investigated in comparison to pure C/C composites. Results indicated that the introduction of h-BN powders into C/C composites significantly reduced the size of PyC and the anisotropy of thermal contraction in matrix, leading to a gradual disappearance of ring defects as the h-BN content increased. In addition, an enhanced interfacial bonding between fiber and matrix obtained due to higher-textured PyC and rougher fiber surface. Thereby, the flexural strengths and modulus of as-prepared composites decreased firstly and then increased, while the impact toughness presented a decreasing tendency as the content of BN powders increased. Furthermore, with the increasing of h-BN content, anisotropies of compressive properties were weakened, and the compressive strength of C/C-BN composites were always higher than that of pure C/C composit. However, when C/C composites modified by 13.5 vol% content of h-BN, excessive loose BN aggregates appeared in C/C-BN composites, leading to a relatively slight reduction of compressive strength.