Alumina microstructural behaviour under pressureless sintering and hot-pressing
Résumé
The aim of this study is to observe the microstructural evolution of a Bayer alumina as a function of different parameters under pressureless sintering and hot-pressing: soaking temperature, soaking time and applied pressure. Experiments indicate a preponderant contribution of the temperature on the microstructure control whatever the sintering mode may be. A semi-manual technique of digitization of the microstructure using a digital tablet allows quantification of the size, the shape and the orientation of the grains. For both sintering modes and beyond a grain size threshold, increase of temperature leads to anisotropic grain growth of the coarser fraction at the expense of the finer fraction. The pressure has an effect on the mobility of grain boundaries and contributes to an elongation that is similar for all the grains. Nevertheless the microstructures under high pressure produce a distribution of strongly elongated grains with an orientation perpendicular to the pressure axis.