Mechanical properties of hot-pressed transparent platelet alumina

The mechanical properties of transparent alumina densified by hot-pressing platelet-morphology powder were characterized and compared to samples using equiaxed (E) powder. The platelet alumina was prepared in two different starting orientations prior to hot-pressing. In the first, the platelets were poured into the die in a non-pre-aligned (NPA) state. In the second, the platelets were pre-aligned (PA) via a separate processing step. The characteristic strength of the NPA, PA, and E samples is 179, 206, and 207 MPA, respectively. The Weibull modulus of the NPA samples is m = 24, which is among the highest Weibull modulus reported for alumina. The Weibull modulus of the NPA samples is higher than the PA and E samples (m = 7 and m = 4, respectively) and is explained by a tighter grain size distribution. The Vickers hardness of the NPA, PA, and E samples were measured both parallel and perpendicular to the hot-pressing direction, with values on the order of 17 GPa, and minimal differences among different samples types. However, the pre-aligned samples exhibited hardness values nearly identical to sapphire in the corresponding crystallographic directions. This is due to the pre-alignment procedure resulting in significant crystallographic orientation in the final sintered parts.