Dislocation mechanism of deformation and strength of Al2O3–YAG single crystal composites at high temperatures above 1500°C

A new unidirectionally solidified eutectic Al2O3–YAG composite has recently been fabricated by accurately controlling the unidirectional solidification. The eutectic composite has a new microstructure, in which single crystal Al2O3 and single crystal YAG are three-dimensionally and continuously connected and finely entangled without grain boundaries. The dislocation structure is observed in both single crystal Al2O3 and YAG in the plastically deformed specimens in the tensile and compressive tests at high temperatures for the Al2O3–YAG single crystal composite, showing that the plastic deformation occurred by dislocation motion. The Al2O3–YAG single crystal composite fabricated has the following properties: (1) the flexural strength at room temperature can be maintained up to just below melting point (about 1830°C), (2) the compressive flow stress at 1600°C and a strain rate of 10−4/s is about 13 times higher than that of sintered composites of the same composition.