New technique for pressureless infiltration of Al alloys into Al₂O₃ preforms

Al alloys were infiltrated into alumina preforms without the aid of pressure in N₂ as well as in air at and above 750 °C. It was possible to eliminate termination of infiltration that was seen in open conditions (where N₂ was in continuous contact with the melt) by modifying the infiltration geometry. This configuration enables the infiltration to continue for longer periods of time, consequently producing greater thickness of composite. In air, Mg placed at the interface getters the in-coming oxygen until the alloy billet melts and seals off the front from the ingress of the furnace atmosphere thereby eliminating the need for prealloying Al with Mg and N₂ atmosphere. In addition, experiments in argon revealed that the infiltration requires some critical amount of N₂ in the atmosphere.