Pressureless infiltration of Al-Mg based alloys into Al2O3 preforms: mechanisms and phenomenology

Al-M based alloys have been infiltrated into Al2O3 preforms by pressureless infiltration in nitrogen atmosphere at and above 800 degreesC. The study r evealed the twin role of Mg in initiation and in continuation of infiltrati on. Mg reduces the alumina layer on the Al-alloy surface thereby bringing a bout the contact between the melt and the preform, which marks the initiati on of infiltration. It has been determined that the premature termination o f infiltration is related to localised depletion at the infiltration front of Mg, which getters the residual oxygen in the nitrogen thereby making the front free of passivating alumina or spinel. Evaporation of Mg from the fr ont and reaction of Mg with the reinforcement are the principal causes for depletion. Two methods have been devised to avoid/delay termination thereby making it possible to fabricate useful section thicknesses with minimal Mg in the alloy. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.