Can orientations of directionally solidified dual-phase Al2O3/YAG eutectics be induced by single-phase sapphire seeds?

Abstract

• The orientations of the dual-phase directionally solidified Al 2 O 3 /Y 3 Al 5 O 12 (YAG) eutectic ceramics were induced successfully by various single-phase sapphire seeds. They show special crystallographic orientation relationships (COR I-IV). • The directions of Al 2 O 3 in the eutectics were governed by the seeds and the YAG in each induced eutectics had a specific growth direction endowed by the Al 2 O 3 in the as-induced eutectics or the sapphire seed. • Based on calculated planar lattice misfits and total interfacial strain energies of four CORs, which indicated that the constraint of the sapphire seed makes the YAG grow following the rule of minimizing the interfacial strain energy. Directionally solidified dual-phase Al 2 O 3 /Y 3 Al 5 O 12 (YAG) eutectic ceramics (DSECs) typically exhibit strong anisotropy. To improve their properties, various single-phase sapphire seeds, including r -axis [11_02], m -axis [101_0], c -axis [0001], and a -axis [112_0], were used as seeds to induce the orientation of the Al 2 O 3 /YAG DSECs. The results showed that Al 2 O 3 in the eutectics could be governed by the sapphire seeds. The YAG in each induced eutectic had a specific growth direction endowed by Al 2 O 3 in the as-induced eutectics or the sapphire seed. Herein, we calculated the planar lattice misfits and interfacial strain energies of four crystallographic orientation relationships based on the constructed lattice models. It was elucidated the constraint of the sapphire seed caused YAG to grow following the rule of minimizing the interfacial strain energy. This revealed the reason why Al 2 O 3 /YAG DSECs orientation can be successfully induced. These results may provide a novel method for the design of high-performance eutectic ceramic materials.