Effect of YSZ with different Y2O3 contents on toughening behavior of Al2O3/Ba-β-Al2O3/ZrO2 composites

Al2O3 matrix composites containing in-situ formed monoclinic zirconia (m-ZrO2) and BaO center dot 7.3Al(2)O(3) (one of Ba-beta-Al2O3 compounds) were prepared via reactive sintering of Al2O3 and BaZrO3 powders. When yttria-stabilized zirconia (YSZ) with Y2O3 contents of 1.5 mol% (1.5YSZ), 2 mol% (2YSZ), and 3 mol% (3YSZ) as well as Y2O3 particles were introduced into Al2O3 and BaZrO3 powder mixtures, the in-situ formed m-ZrO2 was stabilized, resulting from the migration of Y3+ from YSZ or Y2O3 to m-ZrO2 during sintering. The incorporation of YSZ contributed to the refinement of Al2O3 grains, whereas Y2O3-added samples showed larger grain sizes of Al2O3 matrix. The samples with YSZ or Y2O3 addition exhibited high fracture toughness, which is attributed to crack deflection/bridging and transformation toughening of ZrO2. Although the phase transformation is mainly derived from ZrO2 formed during sintering, 1.5YSZ particles added in the composites still showed much higher phase transformability compared to 2YSZ and 3YSZ particles.