Interfacial reaction and nanostructures in Mg matrix composites reinforced with carbon fibers modified by sol-gel method

Continuous carbon fibers (Cf) were modified with γ-Al2O3 and anatase-TiO2 coatings in sol-gel route, and used to prepare 45 vol.% Cf reinforced Mg matrix composites (referred to as Al2O3-Cf and TiO2-Cf composites) using a vacuum pressureless infiltration process, producing the tensile strengths of 550 MPa and 980 MPa, respectively. During the composite fabrication, the Mg matrix reacted with the coatings to form the interfacial layers composed primarily of MgO nanoparticles, with a size of about 10-20 nm and 3-5 nm, respectively, for the Al2O3-Cf and TiO2-Cf composites. Such interfacial reaction produced a volume expansion in the interfacial layer, resulting in the formation of a great deal of crystal defects, such as distorted lattice, dislocation and amorphous intergranular phase. The Al2O3-Cf composite exhibited lower tensile strength due to greater volume expansion in the interfacial layer. A few TiC and TiO2 nanoparticles were observed in the interfacial layer of the TiO2-Cf composite. This is attributed to the restraining effect of the reduced Ti accumulated in the near-interface matrix on the atom diffusion (Mg and Ti), remaining some TiO2 nanoparticles at the surface of Cf. This showed a new self-regulating mechanism of interfacial reaction.