Interface structure in graphite‐fiber‐reinforced metal–matrix composites

Fiber/matrix interfaces in continuous fiber‐reinforced composites are the regions of imperfections, high dislocation densities and residual stresses that affect the material's properties. The interfacial bond integrity, dislocation substructure and precipitate morphology in the interfiber matrix region in diffusion‐bonded graphite–aluminum (Gr–Al), graphite–magnesium (Gr–Mg) and cast Gr–Mg composites has been examined by transmission electron microscopy. This paper discusses the observations of the typical interface structure in Gr–Al and Gr–Mg composites. The Gr–Al composites exhibit different precipitate morphologies (blocky, lath‐shaped and fine cuboidal of similar chemical composition) and Gr–Mg composites show both spherical and lamellar Mg 17 Al 12 precipitates. A typical interface structure in diffusion‐bonded composites exhibits no voids and reaction compounds, whereas in cast Gr–Mg composites patches of microvoids are observed sporadically near the interface, along with Mg 2 Si and MgO phases formed due to the chemical interaction between the matrix and SiO 2 fiber coating. Adjacent to the interface, both Gr–Al and Gr–Mg exhibit a high density of dislocations that can be attributed to the residual stress state generated because of differential contraction between the fiber and matrix during the fabrication process.