DIFFERENT SINTERING ROUTES FOR PREPARING ALUMINA-YTTRIUM ALUMINIUM GARNET NANOCOMPOSITES

摘要

Alumina-yttrium aluminium garnet (YAG) 50 vol. % nanocomposite powders were prepared by a wet-chemical synthesis and characterized by simultaneous DTA-TG, XRD and TEM analyses. Amorphous powders were pre-heated at four different temperatures (namely 600, 800, 900 and 1215 °C) on the ground of the previous characterisation and the influence of this thermal treatment on sintering behaviour, final microstructure and density was investigated. The best performing sample was that pre-calcined at 900 °C, however dense bodies were just yielded by sintering at 1600 °C, resulting in a micronic/slightly sub-micronic microstructure. A pre-seeding step by a fast thermal treatment of the amorphous powder as well as a fast sintering procedure of green compacts, following some literature indications, were also performed as a comparison. Finally, the previously stated thermal pre-treatment of the amorphous product was coupled to its extensive mechanical activation performed by wet planetary/ball milling. This procedure was strongly effective in lowering the densification temperature, so that fully dense alumina/YAG composites, with a mean grain size smaller than 200 nm, were obtained by sintering in the temperature range 1370-1420 °C.