Microstructures of Al/Al₂O₃ composite bodies obtained by reaction between SiO₂ and molten Al at temperatures ranging from 1073 to 1473 K

Al/Al₂O₃ composite bodies were fabricated by reaction between SiO₂ (vitreous silica) rods and molten Al at temperatures between 1073 and 1473 K. Microstructures of the composite bodies were observed using an optical microscope (OM), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Specimens reacted at 1073 K had `feather-like' microstructures consisting of aggregates of Al<sub>2</sub>O<sub>3</sub> grains, which had submicron scales. Specimens reacted at 1173 K had two kinds of microstructures. One was also composed of fine grains and the other had `bone-shaped' Al₂O₃ areas with scales of several micrometers. The latter microstructure became dominant in the specimens reacted above 1273 K. Specimens reacted above 1373 K had microstructures consisting of Al₂O₃ networks which had winding and rounded shapes. According to TEM observation, equi-axed Al₂O₃ grains were connected and had the same crystallographic orientations, and they formed elongated areas in the networks. Formation mechanism of the composite microstructures was discussed by comparing the scales and morphologies of the Al₂O₃ grains at different reaction temperatures.