Directionally solidified eutectic ceramic oxides

Ultra‐High‐Strength Nanofibrillar Al2O3–YAG–YSZ Eutectics

This paper describes a procedure for preparing large surfaces of eutectic composites directionally solidified from the melt, with very fine and uniform microstructures. Large surface plates of the Al 2 O 3 –ZrO 2 eutectic, with thickness up to 250 μm, have been grown by solidification using a modified laser zone melting method suitable for the preparation of large area samples. The surface of a ceramic precursor is scanned with a rectangular CO 2 laser beam of 20×0.5 mm 2 size which induces surface melting. The resulting microstructure is colony free and it consists of fine and alternating interpenetrating Al 2 O 3 and ZrO 2 single crystal lamellae. This microstructure is the basis for improvement of mechanical behaviour in the processed material. The interspacing, crystal structure and orientation relationship between the phases has been determined. Solidification fronts were studied as a function of the processing conditions. A mapping of the residual stresses has also been performed along the transverse plate sections using micro-luminescence techniques.

ZrO2–Al2O3 eutectic plates produced by laser zone melting

The invention relates to uses of glasses and glass-ceramics in dental and orthodontic applications.

Use of ceramics in dental and orthodontic applications

Microstructures in oxide eutectic fibers grown by a modified micro-pulling-down method

Monolithic ceramics are not widely used as structural materials because of their brittleness. Ceramic matrix composites, in which whiskers 1-3 or fibres 4-7 of strong ceramics such as silicon carbide or silicon nitride are embedded in a ceramic matrix, offer improved toughness and strength because the energy of cracks may be dissipated at the whisker/matrik interface. Here we describe a strong ceramic composite with a different kind of microstructure, made by unidirectional solidification of an Al 2 O 3 / GdAlO 3 eutectic mixture. This composite has a microstructure in which continuous networks of single-crystal Al 2 O 3 and single-crystal GdAlO 3 interpenetrate without grain boundaries. Rather than brittle fracture, the material displays plastic deformation at 1,873K owing to dislocation motion, as in metals. The high strength and resistance to brittle failure of this material at such high temperatures augurs well for applications in mechanical engineering.

N. Nakagawa

Papers

A ductile ceramic eutectic composite with high strength at 1,873 K