Comparison among different sintering routes for preparing alumina-YAG nanocomposites

Al2O3-YAG (50 vol.%) nanocomposite powders were prepared by wet-chemical synthesis and characterized by DTA-TG, XRD and TEM analyses. Amorphous powders were pre-heated at different temperatures (namely 600 degrees C, 800 degrees C, 900 degrees C and 1215 degrees C) and the influence of this thermal treatment on sintering behavior, final microstructure and density was investigated. The best performing sample was that pre-calcined at 900 degrees C, which yields dense bodies with a micronic/slightly sub-micronic microstructure after sintering at 1600 degrees C. A pre-treatment step to induce controlled crystallisation of the amorphous powder as well as a fast sintering procedure for green compacts, were also performed as a comparison. Finally, the previously stated thermal pre-treatment of the amorphous product was coupled to an extensive mechanical activation performed by wet planetary/ball milling. This procedure was highly effective in lowering the densification temperature, so that fully dense Al2O3-YAG composites, with a mean grain size smaller than 200 nm, were obtained by sintering in the temperature range 1370-1420 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.