Microstructures, crystallography of interfaces, and creep behavior of melt-growth composites

Oxide eutectic ceramics were prepared from Al2O3 and Ln2O3-based systems by unidirectional solidification from the melt. The microstructure consists of two single-crystal phases continuously entangled in a three-dimensional interpenetrating network without grain boundaries, pores or colonies. The outstanding stability of these microstructures gives rise to a high strength and creep resistance at high temperature. Preferred growth directions, orientation relationships between phases and single-crystal homogeneity of specimens were revealed. Creep behavior at high temperature has been studied, mechanisms of deformation by dislocation motion and twinning were revealed from Transmission Electron Microscopy (TEM) observations. Extension to ternary eutectics with a three-dimensional microstructure consisting in the addition of a toughening phase (ZrO2) to the previous binary eutectics has been investigated. By using this method, significant improvement of fracture toughness was obtained.