Interfacial microstructure and mechanical properties of C_f/AZ91D composites with TiO₂ and PyC fiber coatings

In spite of the effectiveness of the fiber coatings on interface modification of carbon fiber reinforced magnesium matrix composites, the cost and exclusive equipment for the coatings preparation are usually ignored during research work. In this paper, pyrolytic carbon (PyC) and TiO₂ were coated on carbon fiber surface to study the effects of fiber coatings on interfacial microstructure and mechanical properties of carbon fiber reinforced AZ91D composites (C_f/AZ91D composites). It was indicated that both the two coatings could modify the interface and improve the mechanical properties of the composites. The ultimate tensile strength of the TiO₂-C_f/AZ91D and the PyC-C_f/AZ91D composite were 333MPa and 400MPa, which were improved by 41.7% and 70.2% respectively, compared with the untreated-C_f/AZ91D composite. The microstructure observation revealed that the strengthening of the composites relied on fiber integrity and moderate interfacial bonding. MgO nano-particles were generated at the interface due to the reaction of TiO₂ with Mg in the TiO₂-C_f/AZ91D composite. The volume expansion resulting from the reaction let to disordered intergranular films and crystal defects at the interface. The fibers were protected and the interfacial reaction was restrained by PyC coating in the PyC-C_f/AZ91D composite. The principle to select the coating of fiber was proposed by comparing the effectiveness and cost of the coatings.