Rapid solidification of Al₂O₃/Y₃Al₅O₁₂/ZrO₂ eutectic in situ composites by laser zone remelting

Directionally solidified rods and plates of Al₂O₃/YAG/ZrO₂ ternary eutectic in situ composites were grown by the laser zone remelting technique under different growth conditions, aiming to reveal the effect of rapid solidification on the microstructure characteristics, solidification behaviors and mechanical properties. The as-solidified eutectics presented smooth surfaces, well-defined phases, no pores and grain boundaries in their microstructures. The eutectic microstructure displayed a refined entangled network of Al₂O₃ (40%), YAG (43%) and ZrO₂ (17%) phases with sizes in the submicron range. Moreover, the refined ordered/aligned eutectic structure with the lamellar/fibrous and rod-type ZrO₂ in the nano-micron range was also observed. Two kinds of microstructures primarily resulted from the high-temperature gradient and solidification rate of the laser zone remelting. The eutectic interspacing decreased with increasing the scanning rate and the minimal spacing observed was as fine as 0.1-0.2 μm. The eutectic interfaces showed a typical faceted/faceted growth characteristic and the formation mechanism was detailedly discussed. The mechanical characterization at ambient temperature showed that the hardness and fracture toughness of the eutectic were 16.67 GPa and 8.0 MPa m^1/2, respectively. The small size effect of eutectic phases related with the rapid solidification, the addition of the third component of ZrO₂ and the crack deflection contributed to the improved fracture toughness.