Directed metal oxidation is a new technique for the fabrication of ceramic matrix composites that advantageously utilizes the high temperature oxidation of liquid metals. This technique is known as DIMOX™ or Lanxide™ process. It is believed to potentially reduce the present limitations of conventional ceramic technology and offer the ability to make bodies having low porosity.
For $Al_2O_3/Al$ composites, rapid oxidation reaction is promoted by introduction of minor elemental or oxide powder as dopants. It was reported that Mg was critical dopant. In this work, the role of Mg in the formation of $Al_2O_3/Al$ composites was studied.
Directed reaction was proceeded at 800 - 300℃ for 3 hours in air atmosphere using Al alloys containing 5 wt% of Mg.At temperature below 1100℃, the surface oxides of alloy was covered with $MgAl_2O_4$ and MgO that prevented the formation of dense $Al_2O_3/Al$ protective film.
After a period of incubation, bulk growth occurred at the interface between the surface oxides and gaseous oxidant. The interface between metal pool and growth product was composed of $MgAl_2O_4$ and Al alloy phases. The alloy phase was three-dimensionally interconnected. Therefore, it is believed that molten metal has been supplied to outer growing surface through this metal channel.
Growing surface front was detected to be composed of $MgAl_2O_4$ and MgO by XRD analysis. Under this layer, Al alloy and $Al_2O_3$ coexisted with three-dimensionally interconnected structure.
From this result, it is thought that Mg in Al alloy was consumed to the formation of $MgAl_2O_4$ and MgO phases, which prevented the formation of $Al_2O_3$ protective film at the initial alloy surfaces and outer growing surfaces.
