Seed-crystal-induced directional solidification toward Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12/ZrO2 ternary eutectic ceramics

Abstract

The present work successfully prepared a novel Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12/ZrO2 (or Al2O3/(5RE0.2)AG/ZrO2 in short) ternary eutectic ceramic with the seed-crystal-induced technique by directional solidification. ZrO2 was a cubic structure and was stabilized by all oxides of Y2O3, Er2O3, Yb2O3, Ho2O3, and Lu2O3. The three phases interpenetrated each other and ZrO2 was highly dispersed. Al2O3 inherited well the direction of the c-sapphire seed. The orientation relationship among the three was determined to be [0001]Al2O3 || [100](5RE0.2)AG || [110]ZrO2, (11–20)Al2O3 || (004)(5RE0.2)AG || (002)ZrO2. The three interfaces were all semi-coherent and showed higher interfacial misfit strain energy due to the solid solution effect of (5RE0.2)AG. The novel Al2O3/(5RE0.2)AG/ZrO2 ternary eutectic ceramic showed improved mechanical properties compared to other Al2O3-based eutectic ceramics. The solid solution effect was the main reason for its enhanced hardness and elastic modulus. Several toughening mechanisms including crack bridging, bifurcation, deflection, and screening can be found in the Al2O3/(5RE0.2)AG/ZrO2 ternary eutectic ceramic. The micro-scale suture-like deflection was newly found in the microstructure, which contributed to its fracture toughness.