Development of formation method for homogeneous and fine eutectic like microstructures with off eutectic composition in various rare earth oxide–Al 2 O 3 systems

Abstract

Homogeneous and ultrafine eutectic like microstructures without coarse primary crystals were formed by a crystallisation of amorphous phases for several rare earth (RE) oxide–Al₂O₃ eutectic systems with the off eutectic compositions. Mixtures of RE oxide and Al₂O₃ powders with the off eutectic compositions were melted and quenched rapidly to form the amorphous phases. A heat treatment of the amorphous phases at 1000 and 1300°C for 30 min formed RE₃Al₅O₁₂/Al₂O₃ (or REAlO₃/Al₂O₃) phases. This method utilises a low migration rate in the amorphous phases. SEM observation of these materials heat treated at 1300°C showed homogeneous eutectic like microstructures. Formation of primary crystals, which are always formed in the ordinal off eutectic microstructure, was absolutely suppressed. Furthermore, the microstructures were much finer than those of materials ordinarily prepared from eutectic melts.