Microstructure and mechanical properties of directionally solidified Al2O3/GdAlO3 eutectic ceramic prepared with horizontal high-frequency zone melting

摘要

Directionally solidified eutectic oxide ceramics are very promising as a next-generation structural material for ultrahigh-temperature applications, above 1600 degrees C, owing to their outstanding properties of high corrosion resistance, oxidation resistance, high fracture strength and toughness, and high hardness. Herein, Al2O3/GdAlO3 eutectic ceramic was prepared with horizontal high-frequency induction zone melting (HIZM), and the effects of the processing parameters on the eutectic microstructure and mechanical properties were investigated. The results indicated that the directionally solidified Al2O3/GdAlO3 eutectic ceramic was composed only of the Al2O3 phase and GdAlO3 phase penetrating mutually, and the Al2O3 phase was the substrate in which the GdAlO3 phase was embedded. As the solidification rate increased from 1 to 5 mm/h, the eutectic microstructure underwent a transformation from an irregular pattern to a relatively regular "rod" or "lamellar" pattern, and the eutectic spacing constantly decreased, reaching a minimum value of 0.5 mu m. The eutectic ceramic hardness and fracture toughness at room temperature increased continuously, reaching 23.36 GPa and 3.12 MPa.m(1/2), which were 2.3 times and 2.5 times those of the sintered ceramic with the same composition, respectively. Compared with the samples obtained from vertical high-frequency induction zone melting, the orientation of eutectic phases along the growth direction decreased significantly, and the size uniformity of the GdAlO3 phase became poorer in the samples prepared with HIZM at the same solidification rate; nevertheless, the hardness and fracture toughness of the samples increased by 11% and 63%, respectively.