Effect of growth rate on the microstructure and mechanical behavior of directionally solidified Y3Al5O12/MgAl2O4 eutectics

• YAG/MgAl2O4 eutectic oxides for high temperature applications have been successfully fabricated by directional solidification and zone melting method.
• We have investigated the dependence of solidification parameters on the high temperature mechanical behaviors.
• The optimal hardness/toughness ratios could be obtained by growth rates of 5 mm/min.
• Thermal expansion behaviors of YAG/spinel are remarkably independent of the solidification parameters.
• The uniform lamellar microstructures are formed under intermediate growth conditions on YAG/spinel eutectics.

The mechanical properties of YAG–spinel (Y3Al5O12/MgAl2O4) eutectic rods were studied as a function of the solidification rate. Eutectic rods were grown by a laser-heated floating zone method. YAG–spinel eutectic rods measuring 2 mm in diameter and 200 mm in length were grown at rates of 0.1–10 mm/min with a temperature gradient of approximately 1×104 K/m. The compressive creep strength of a crystal grown at a rate of 5 mm/min and a flow rate of 1.2 mm/min at 1500 °C under a strain rate of 1.0×10−4 was only 398 MPa, which is slightly higher than that of crystals grown under different conditions. The highest flexure strength of the Y3Al5O12/MgAl2O4 material at ambient temperature was obtained at a growth rate of 5 mm/min. The maximum hardness reached 16.7 GPa, and the room fracture toughness was 3.9 MPa m1/2. The changes in the mechanical behavior and the microstructure of the material that occurred at different growth rates are briefly discussed.