Growth of Al2O3/Al Composite by Directed Metal Oxidation of Al Surface Doped with Sodium Source

Both an unreinforced Al₂O₃/Al matrix and a α-Al₂O₃ particulate reinforced composite have been produced by the oxidation of an Al surface doped with NaOH in the absence of any other dopant. Fabrication of the matrix was initiated by the formation of NaAlO₂, which provides a favorable surface structure for the matrix formation by breaking the protective Al₂O₃ layer on Al. During the matrix growth, the external surface of the growth front was covered with a very thin sodium-rich oxide. A cyclic formation process of the sodium-rich oxide on the growth surface was proposed for the sodium-induced directed metal oxidation process. This process involves dissolution of the sodium-rich oxide, motion of Na to the growth front, and re-formation of the oxide on the surface. Near-net-shape composites were fabricated by infiltrating an Al₂O₃/Al matrix into a α-Al₂O₃ particulate preform, without growth barrier materials. The infiltration distance increased almost linearly in the NaOH-doped preform.