Characterization of interfacial mechanical properties in carbon fiber/aluminium matrix composites by the nanoindentation technique

Interfacial mechanical properties in an AA6061 reinforced with short carbon fibers coated with different metallic films by electroless were investigated using the nanoindentation technique. Copper and nickel coatings on carbon fibers surface were applied to control the interfacial reactivity of fibers with the molten aluminium during composite manufacture, jointly with the objective of improving its wetting behaviour. Because of the coating, local microstructure of the composites can be significantly altered, creating differences between the properties of the interphase regions and the bulk composite. Nanoindentation is a suitable technique to measure hardness and elastic modulus profiles on a micrometric range. Besides, from nanoindentation tests, information on interfacial fracture mechanisms can be obtained. Three types of nanoindentation tests were carried out for the interfacial mechanical characterization: (1) nanoindentation profiles across the matrix/fiber interfaces to determine changes in hardness and elastic modulus of the modified matrix; (2) single indentations in the interface proximity to evaluate the interfacial fracture tendency; and (3) individual push-out tests on perpendicularly aligned fibers to the composite surface, to measure the interfacial shear strengths. SEM and TEM studies at the interfacial zones were applied to relate the change in mechanical properties with the interfacial formation mechanisms.