INTERFACIAL REACTIONS IN MG-CONTAINING ALUMINUM-ALLOYS MULLITE-ZIRCONIA REACTION-SINTERED COMPOSITES

Commercial mullite as well as reaction sintered mullite-zirconia bars, obtained by the authors, were exposed to Mg-containing molten aluminu m alloy at 800 degrees C for 500-1000 h and afterwards characterized b y XRD, RLOM, TEM and SEM-EDS. Munite was completely attacked, by Al pe netrating through grain boundaries and reducing the mullite grains to alumina and silicon. Mullite-zirconia was not attacked, because the de nse net of ZrO2-grains prevented penetration of molten metal into the compact and consequently a mechanically and thermodynamically stable s pinel layer (approximate to 30 mu m) was formed at the static interfac e which protected the ceramics against Further attack. (C) 1998 Acta M etallurgica Inc.