Orientation relationship formation in a uni-directionally solidified Al₂O₃/Ln₃Al₅O₁₂(Ln = Y, Er) eutectic system

Formation of the orientation relationship for uni-directionally solidified Al₂O₃/Ln₃Al₅O₁₂ eutectic system at early stage of the solidification was examined. Ln₃Al₅O₁₂ was the first phase to nucleate in the Al₂O₃/Ln₃Al₅O₁₂ eutectic microstructure. When the Ln₃Al₅O₁₂ phase nucleated as the primary phase, no specific orientation for the Al₂O₃ and Ln₃Al₅O₁₂ phases with respect to the solidification direction was formed, and the coupled eutectic growth occurs like polycrystalline. On the other hand, in the case of Al₂O₃ phase nucleated as the primary phase, a specific orientation for Al₂O₃ and/or Ln₃Al₅O₁₂ was easily formed. The orientation relationship <100>_Al2O3 || <100>_Ln3Al5O12 || <solidification direction> was obtained.