Comparison among different sintering routes for preparing alumina-YAG nanocomposites

Al2O3-YAG (50vol.%) 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◦C, 800◦C, 900◦C and 1215◦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◦C, which yields dense bodies with a micronic/slightly sub-micronic microstructure after sintering at 1600◦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°C.