THE INTERFACE AND INTERPHASE IN CARBON-FIBER-REINFORCED COMPOSITES

High resolution transmission electron microscopy in association with mechanical tests (interlaminar shear strength) has been used to characterize the surface of polyacrylonitrile-based (PAN-based) carbon fibres and the interface in carbon fibre-reinforced polymer composites. These composites were made of commercial high strength Courtaulds fibres used without any surface treatment, with a commercial oxidative treatment, and with an amine treatment. The observations showed that PAN-based carbon fibre surfaces are composed of basal plane domains separated by edge planes and disorganized regions. The structure of the interface depends on the nature of the surface treatment. Untreated fibres are constituted mainly of basal planes, while the interface becomes hairy with lots of edges after oxidative treatment. The amine treatment resulted in an intermediate structure for the interface with both basal and edge planes. The adhesion between fibre and matrix is dependent on the surface treatment. A qualitative correlation has been established between the characteristics of the interface and the mechanical properties.