Simultaneous improvements in flexural strength and ductility of carbon nanotube-doped carbon/carbon composites by depositing a pyrocarbon layer on carbon fibers

Introducing carbon nanotubes (CNTs) on carbon fibers (CFs) can significantly improve the matrix-dominated mechanical strength of carbon/carbon composites (C/Cs). As for the CF-dominated mechanical properties such as flexural property, however, the direct introduction of CNTs on CFs always leads to a humble improvement of flexural strength and a brittle fracture mode of the composites. To overcome this limitation, in this work, a thin medium-textured pyrocarbon (PyC) coating, as an interphase layer, was deposited on CFs by isothermal chemical vapor infiltration (ICVI) and its effects on flexural property of CNT-doped C/Cs (CNT-C/Cs) were investigated. Results show that CNT-C/Cs with ICVI PyC layer (PCCT) have a 1100% improvement in flexural ductility and a 44.3% improvement in flexural strength, compared with CNT-C/Cs without ICVI PyC layer (CCT), which are attributed to the toughening role of CFs through their pullouts and the strengthening role of CNTs on the composites. This work could pave a meaningful way for the development of CNT-C/Cs with high mechanical strength and good toughness.