Growth and characterization of nanostructured Al_2O_3/YAG/ZrO_2 hypereutectics with large surfaces under laser rapid solidification

摘要

The preparation of large bulk oxide eutectics with homogeneous and dense structure in nano-scale by melt growth method is a difficult challenge. Fully dense, homogeneous and crack-free ternary nanostructured Al_2O_3/YAG/ZrO_2 hypereutectic plate with large surface is successfully obtained by laser remelting. The hypereutectic in selected composition presents an ultra-fine eutectic-like microstructure consisting of alternating interpenetrating Al_2O_3, YAG and ZrO_2 lamellae with mean interphase spacing of about 150 nm, which is much smaller than the ternary eutectic composition grown at the same growth conditions. With the increase of laser scanning rate, the lamellar spacing is rapidly decreased. The minimum V.Alue obtained is 50 nm. The analysis indicates that the strong faceted growth behavior and cooperative branching of the component phases related with high entropies of fusion and large kinetic undercooling during laser rapid solidification are the primary formation reasons for the irregular eutectic growth morphology. Furthermore, the unique cellular microstructure with complex structure is also observed at high growth rate, and their formation mechanism and effect of the composition on the microstructure are discussed.