Microstructure and improved mechanical properties of Al2O3/Ba-β-Al2O3/ZrO2 composites with YSZ addition

Al2O3/Ba-β-Al2O3/ZrO2 composites were fabricated by solid-state reaction sintering of Al2O3, BaZrO3, and yttria stabilized zirconia (YSZ) powders. The effects of YSZ addition on microstructure and mechanical properties have been investigated. The incorporation of YSZ promoted the densification of the composites and formation of tetragonal ZrO2 phase. The microstructure of the composites was characterized by elongated Ba-β-Al2O3 phase and equiaxed ZrO2 particles including added YSZ and reaction-formed ZrO2. The Al2O3/Ba-β-Al2O3/ZrO2 composites with YSZ addition exhibited improved fracture toughness, as a result of multiple toughening effects including crack deflection, crack bridging, crack branching, and martensitic transformation of ZrO2 formed by the reactions between Al2O3 and BaZrO3. Moreover, owing to the grain refinement of Al2O3 matrix, dispersion strengthening of the added YSZ particles, and an increase in density of the composites, the Vickers hardness and flexural strength of Al2O3/Ba-β-Al2O3/ZrO2 composites were dramatically enhanced in comparison with the composites without YSZ addition.