Compressive and interlaminar shear properties of carbon/carbon composite laminates reinforced with carbon nanotube-grafted carbon fibers produced by injection chemical vapor deposition

Carbon nanotubes (CNTs) were grown in situ on the surface of carbon fiber cloths by injection chemical vapor deposition using ethanol as a carbon source and ethylenediamine as a promoter. The nanotube-grown cloths were stacked to form multilayered preforms, and then densified by isothermal chemical vapor infiltration to prepare CNT reinforced carbon/carbon (CNT-C/C) composite laminates. The effect of CNTs on microstructure and mechanical properties of carbon/carbon (C/C) laminates were investigated. Results show that the existence of CNTs not only contributes to refine the pyrocarbon (PyC) grain size but also inhibits matrix cracking, resulting in high cohesion of PyC matrix. The grown CNTs possess high surface area thus modifying the fiber surface condition, which in turn improves the fiber/matrix (F/M) interface. Both the high matrix cohesion and strong F/M interface bonding give rise to the powerful interaction between adjacent layers in the CNT-C/C laminates. The measured out-of-plane, in-plane compressive strength and interlaminar shear strength of these laminates show a significant enhancement of 32%, 115% and 108%, respectively compared with the laminates without CNTs. Out-of-plane and in-plane compressive modulus of these laminates are also improved by 11% and 46%, respectively.