Mechanical properties of hot‐pressed transparent platelet alumina

Abstract 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.