INSITU ALUMINA ALUMINATE PLATELET COMPOSITES

Alumina composites containing in-situ-formed hexaluminate (LaAl11O18, LaMgAl11O19, SrAl12O19, and Mg2NaAl15O25) platelets can be pressureless-sintered to high density. The grain morphology of the aluminates can be controlled by composition. A peak toughness 50% higher than that of alumina is obtained at 30 vol% aluminates, with a modest reduction (10%) in hardness and Young's modulus. Although crack-bridging by aluminate platelets is apparently operating, the maximum toughness is intrinsically limited by the low cohesive strength of these layer compounds.