New Ceramic Composite from a Multioxide Eutectic Melt
- PDF / 72,519 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 39 Downloads / 162 Views
New Ceramic Composite from a Multioxide Eutectic Melt Jose M. Calderon-Moreno and Masahiro Yoshimura Center of Materials Design, Tokyo Institute of Technology Nagatsuta 4259, Midori-ku, 226-8503 Yokohama, Japan. ABSTRACT New high temperature ceramic eutectic composites have been obtained. The composite is self-assembled in one quick step by rapid supercooling of the multioxide alumina-YAG-zirconia eutectic in an arc-image lamp furnace. The new material will find applications as in-situ coating and component for use at ultra-high temperature. Periodic self-assembled layered structures kinetically forced to solidify with interspacing in the submicron range will result in very interesting properties and applications for high temperature multioxide oxide eutectic composites, offering the challenge of design of layered nanostructures tailored to specific applications by kinetic control during solidification.
INTRODUCTION Oxides ceramics have intrinsic properties such as oxidation resistance, chemical and thermal stability. However, they also have poor resistance to thermal shock and in general to crack propagation and growth, which results in rapid material degradation and catastrophic fracture. One successful approach to improve the thermo-mechanical stability of ceramic oxide composites has been their fabrication by solidification from eutectic melts. Eutectic composites fabricated by unidirectional solidification have excellent strength and creep resistance at high temperature. The strengthening of grain boundaries characteristic of eutectics is especially required for long-term service in high temperature applications. The refining of the microstructure in eutectic composites with thinner lamella size will result in higher strength by reduction in flaw size, inhomogeneities and stress accumulation points. However the fabrication of oxide eutectics by more rapid solidification techniques has yielded moderate success, producing partially amorphous or inhomogeneous samples, because it is difficult to maintain a homogeneous heat transfer at high cooling rates [1-6]. Therefore rapid solidification methods have been used to fabricate eutectic powders, but not layered eutectic crystals. The smaller lamella sizes in eutectic composites by unidirectional solidification are in the few microns range. The aim of this work is to obtain a eutectic composite with lamella size in the sub-micron range, by using rapid solidification in an arc-image furnace.
EXPERIMENTAL Starting materials were prepared from high purity (>99.9%) ZrO2, Y2O3 and Al2O3 powders by dry and wet mixing in methanol using an alumina mortar. A constant alumina to zirconia ratio of 79:21 and different yttria contents were used for the initial powders mixtures. Pellets of the mixed powders were placed on a copper plate cooled by water and melted in air in an arc-image lamp furnace by the radiation of a Xe lamp (Ushio UF-10001). The spherical arc-melted B6.2.1
specimen was quenched by rapidly moving the copper plate from the focal point. The cooling rate using
Data Loading...
