Strengthening of C/SiC Composites by Electrophoretic Deposition of CNTs on a SiC Coating

The current study reports the enhancement of mechanical properties of carbon fiber-reinforced silicon carbide ceramic matrix composites (C/SiC CMCs) by the application of a carbon nanotube/silicon carbide (CNT/SiC) coating. CNTs were deposited on the surfaces of C/SiC composites using electrophoretic deposition (EPD), after which infiltration by SiC was achieved through a chemical vapor infiltration process. An EPD duration of 5 min was associated with a 40% increase in the ultimate flexural strength relative to that of composites with a pure SiC coating. The observed enhancement was rationalized by the microstructural observations of SiC infiltration into the porous CNT morphology and the subsequent formation of CNT/SiC layers on the surfaces of the composites and by the inherent toughness of the SiC whiskers. The flexural strength decreased with EPD durations greater than 5 min due to the formation of thick CNT meshes, which decreased the open porosity and thereby obstructed further SiC infiltration. This is a viable methodology for the improvement of mechanical properties of CMCs by the introduction of a ceramic coating containing CNT.