Preparation and microstructure of large-sized directionally solidified Al2O3/Y3Al5O12 eutectics with the seeding technique

A large-sized Al2O3/Y3Al5O12 (YAG) eutectic single crystal is successfully prepared with the external seed by a modified Bridgman furnace. The microstructure, crystallography and interface structure of the large-sized Al2O3/YAG eutectic are well investigated. It is found that the longitudinal eutectic microstructure shows large length-to-width phase ratios. The crystallographic orientation relationship of the as-obtained large-sized Al2O3/YAG eutectic is consistent with that of the seed. The epitaxial solidification of the binary eutectic occurs, and the dominating of the seed is not lost in the long-range growth. The observed Al2O3/YAG interface structure is studied by near-coincidence site lattice (NCSL) theory. The volume strain for the NCSL is very low (0.02), which suggests that the interfaces have locally low interfacial energies. This small volume strain might be the reason for stable induced-growth along the seed.