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Abstract
Oxide directionally solidified eutectic ceramics (DSECs) have excellent mechanical properties, oxidation resistance, and ablation resistance in an ultra-high temperature environment above 1600 °C. In this study, Al2O3/Er3Al5O12/ZrO2 ternary DSECs were prepared by high-frequency induction zone melting. Their diameters were considerably greater than those of samples prepared with other processing techniques under the conditions where the microstructures were uniform. The component, microstructure, and mechanical properties in these samples were investigated. The results indicate that these DSECs were composed of only Al2O3, Er3Al5O12, and ZrO2 phases. As the solidification rate increased, both the eutectic phase size and eutectic spacing decreased continuously, and the microstructure was refined. The relationship between the eutectic spacing and solidification rate satisfied the formula λ2ν ≈ 33.8 ± 0.49. A polygonal colony structure appeared at a growth rate of 6.7 μm/s, which was associated with the uneven distribution of the temperature field. The hardness and indentation fracture resistance increased marginally with an increase in solidification rate, achieving 17.6 ± 0.8 GPa and 5.0 ± 0.5 MPa·m1/2, respectively. The hardness of the Al2O3/Er3Al5O12/ZrO2 ternary DSEC was 18.3% less than that of the Al2O3/Er3Al5O12 binary DSEC owing to the reduced hardness of the ZrO2 phase added in the eutectic composition. The ternary DSEC's indentation fracture resistance was 88.4% greater than that of the binary eutectic ceramic owing to the phase transformation toughening of the ZrO2 phase.
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