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.