Phase growth patterns for Al2O3/GdAlO3 eutectics over wide ranges of compositions and solidification rates

Abstract

Phase selection and growth characteristics of directionally solidified Al2O3/GdAlO3 (GAP) faceted eutectic ceramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled zone. Through the observation of the quenched solid-liquid interface, the competitive growth of primary faceted Al2O3 phase, primary non-faceted GAP phase and Al2O3/GAP eutectic with different morphologies is detected. Microstructure transitions from wholly eutectic to primary Al2O3 (GAP) dendrite plus eutectic and then to wholly eutectic are found in Al2O3-20 mol% Gd2O3 hypoeutectic (Al2O3-26 mol% Gd2O3 hypereutectic) ceramics with the increase of solidification rate. The dendrite growth of faceted Al2O3 and non-faceted GAP phases are well predicted by KGT model, which have introduced appropriate dimensionless supersaturation Ω to characterize the anisotropic growth of dendrites. Based on the maximum interface temperature criterion, the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al2O3/GAP eutectic ceramics is in good agreement with the experimental results. Besides, the influence of microstructure with these different morphologies on the flexural strength of Al2O3/GAP eutectic ceramics is studied.