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

Abstract Al 2 O 3 /Lu 3 Al 5 O 12 (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 Al 2 O 3 /LuAG were characterized, and the mechanical properties (Vickers hardness and fracture toughness) were compared with those of Al 2 O 3 /REAG (RE = Y, Er, and Yb). Results show that Al 2 O 3 /LuAG with solidification rate of 30 mm/h has established preferred growth direction in both Al 2 O 3 and LuAG phases with cellular eutectic structures. While Al 2 O 3 /LuAG with solidification rate of 10 mm/h only shows preferred growth direction in Al 2 O 3 phase and presents degenerate irregular eutectic microstructures. Besides, Al 2 O 3 /LuAG exhibits higher hardness compared with Al 2 O 3 /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 Al 2 O 3 /REAG, revealing the possibility and feasibility of microstructure control and mechanical properties optimization for DSE Al 2 O 3 /REAG ceramics by tailoring the rare earth elements.