Elaboration and microstructural characterization of a mullite-zirconia composite obtained by reaction sintering
Résumé
A significant toughening could be obtained by incorporating zirconia (ZrO2) particles in a mullite matrix (3Al2O 3.2SiO2). The mechanism involved in the toughening of mullite composites by zirconia addition is a stress-induced structural transformation of zirconia (tetragonal to monoclinic). In this work, we elaborated by reaction sintering a mullite-zirconia composite from a stoichiometric powder mixture of monohydrated alumina (Boehmite AlOOH) and zircon (ZrSiO4). Reactions and phase transformations during the powder sintering were studied by dilatometry, DTA-TGA, XRD and SEM. The dilatometric curves and differential thermal analysis showed several microstructure transformations in these mixtures. From the X-ray diffractograms, we put in evidence the zircon decomposition (into zirconia and silica) and the mullite-zirconia composite formation, by reaction sintering (with the boehmite), starting from a temperature of 1450°C. The micrographic observations of the samples showed also a presence of dispersed fine zirconia particles of rounded shape in the mullite matrix.