Anisotropic compressive properties of CNT/SiC composites produced by direct matrix infiltration of vertically aligned CNT forests

Carbon nanotube-reinforced silicon carbide composites (CNT/SiC) produced by direct infiltration of matrix into a porous CNT arrays have been demonstrated to possess a unique microstructure and excellent micro-mechanical properties. Here, the study reports on the anisotropic compressive behavior of vertically aligned CNT-reinforced SiC composites (VACNT/SiC) produced by chemical vapor infiltration (CVI) of SiC matrix into the VACNT forests. Findings demonstrate that the longitudinal and transverse compressive strengths of VACNT/SiC specimens with a density of 1.54 g/cm³are 160 ± 16 and 41 ± 3 MPa, respectively. No matter which compressive mode they all exhibit a typical ductile failure with a similar load-displacement behavior but the stress concentration level of the transverse compression is lower than that of the longitudinal. The mechanisms describing the enhanced strength of these composites were clarified by examining the morphologies of fracture surfaces under scanning electron microscope. CNT pull-out, bridging, sequential breaking and slippage of the walls of the CNT during failure were consistently observed in all fractured specimens.