In‐Situ Alumina/Aluminate Platelet Composites

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Abstract
Alumina composites containing in‐situ‐formed hexaluminate (LaAl 11 O 18 , LaMgAl 11 O 19 , SrAl 12 O 19 , and Mg 2 NaAl 15 O 25 ) 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.