Preparation, microstructures, and mechanical properties of directionally solidified Al₂O₃/Lu₃Al₅O₁₂ eutectic ceramics

Abstract

Al2O3/Lu3Al5O12 (LuAG) directionally solidified eutectic (DSE) ceramics with two solidification rates were prepared utilizing optical floating zone (OFZ) technique. The microstructures (eutectic morphology, preferred growth direction and interface orientation) of Al2O3/LuAG were characterized, and the mechanical properties (Vickers hardness and fracture toughness) were compared with those of Al2O3/REAG (RE = Y, Er, and Yb). Results show that Al2O3/LuAG with solidification rate of 30 mm/h has established preferred growth direction in both Al2O3 and LuAG phases with cellular eutectic structures. While Al2O3/LuAG with solidification rate of 10 mm/h only shows preferred growth direction in Al2O3 phase and presents degenerate irregular eutectic microstructures. Besides, Al2O3/LuAG exhibits higher hardness compared with Al2O3/REAG (RE = Y, Er, and Yb). In addition, a special attention is focused on the relations among rare earth ionic radius, eutectic microstructures, and mechanical properties of these DSE ceramics. It is demonstrated that a smaller rare earth ionic radius could lead to larger eutectic interspacing as well as higher Vickers hardness of DSE Al2O3/REAG, revealing the possibility and feasibility of microstructure control and mechanical properties optimization for DSE Al2O3/REAG ceramics by tailoring the rare earth elements.

Dendrite microstructure formation and enhanced toughness in high‐entropy REAlO3–RE2Zr2O7 eutectic oxide

“…The formation of dendritic structures at the eutectic composition is a common phenomenon in refractory oxide composites, in contrast to eutectic coupled‐growth structures such as “Chinese script” structures, lamellae, and rod structures 2,9,10,13,29–31 . The formation of dendrites occurs due to the breakdown of the stable eutectic coupled growth.…”

“…The formation of dendritic structures at the eutectic composition is a common phenomenon in refractory oxide composites, in contrast to eutectic coupled-growth structures such as "Chinese script" structures, lamellae, and rod structures. 2,9,10,13,[29][30][31] The formation of dendrites occurs due to the breakdown of the stable eutectic coupled growth. The growth competition between singlephase dendrites and eutectic coupled growth is widely discussed, 1,7 and the growth pattern selection of eutectic or dendrite is thought to be determined by the interphase temperature of the precipitate phase tip.…”