Microstructure and mechanical properties of a directionally solidified Al₂O₃/Y₃Al₅O₁₂/ZrO₂ hypoeutectic in situ composite

Directionally solidified ternary Al₂O₃/Y₃Al₅O₁₂(YAG)/ZrO₂ hypoeutectic rod composites were successfully fabricated by the laser zone remelting technique. The microstructure and mechanical properties of the composite were investigated. The microstructure presented a complex three-dimensional network structure consisting of fine Al₂O₃ (41 vol.%) and YAG (49 vol.%) phases, with smaller ZrO₂ (10 vol.%) phases partially distributed at the Al₂O₃/YAG interfaces. The irregular growth behavior in the hypoeutectic was revealed. The hardness and fracture toughness at ambient temperature were measured to be 17.3 GPa and 5.2 MPa m^1/2, respectively. The toughness enhancement in comparison with previous binary Al₂O₃/YAG composites was mainly attributed to the refined microstructure, and crack deflection, branching and bridging. Moreover, the residual stresses, generated by different thermal expansion coefficients of the component phases, also importantly contributed to the improved toughness. Correlations between the addition of the third component ZrO₂ and the microstructure and properties were discussed as well.