Rapid solidification behaviour of Al₂O₃/Y₃Al₅O₁₂ (YAG) binary eutectic ceramic in situ composites

Rapid solidification of Al₂O₃/Y₃Al₅O₁₂ (YAG) binary eutectic ceramic in situ composites during the remelting process using high-energy laser, which results in refinement of the solidification microstructure and improvement of the mechanical properties, is studied in this paper. The rapidly solidified Al₂O₃/YAG eutectic consists of Al₂O₃ and YAG phases without any other phases, effectively avoiding grain boundaries. The eutectic interspacing is extremely refined due to the high-temperature gradient and solidification rate of laser rapid solidification, and the minimal interspacing is as fine as 0.5 μm. The eutectic exhibits an obvious faceted-faceted eutectic growth characteristic which mainly derives from the high-fusion entropies of eutectic phases and large kinetic undercooling. The mean hardness and fracture toughness measured by an indentation technique are 17.5 GPa and 3.6 MPa m^1/2, respectively. The increase of fracture toughness can be attributed to the refinement of eutectic phases which restrain and arrest crack propagations.