Microstructure and mechanical properties of in situ synthesized alumina/Ba-β-alumina/zirconia composites

A new alumina matrix composite has been synthesized via in situ reactive sintering of Al2O3 and BaZrO3 powders. Phases formed in situ were Ba-β-Al2O3 (BaO·7.3Al2O3) (a so-called hexaaluminate compound) with a layered β-Al2O3 structure and monoclinic ZrO2. The Ba-β-Al2O3 phase exhibited an elongated morphology, while ZrO2 was primarily present in an equiaxed form. Composites of Ba-β-Al2O3, ZrO2 and alumina encouraged crack deflection and crack bridging, thus improving the mechanical properties beyond those of monolithic alumina. The alumina-based composite with 30% Ba-β-Al2O3 and ZrO2 showed an optimum combination of mechanical properties: high strength, large work of fracture, and improved fracture toughness.