SYNTHESIS OF CERAMIC EUTECTICS USING MICROWAVE PROCESSING Anton V. Polotai, Jiping Cheng, Dinesh K. Agrawal, Elizabeth C. Dickey* and Sheldon Cytron** Materials Research Institute, the Pennsylvania State University, University Park, PA, 16802 * Department of Materials Science and Engineering, the Pennsylvania State University, University Park, PA, 16802 ** U.S. Army TACOM-ARDEC, Picatinny, NJ 07806 ABSTRACT This communication presents preliminary results of using microwave energy in order to melt and re-solidify oxide and non-oxide refractory ceramic eutectic compositions in an appropriate crucible. The Al 2 O 3 –Y 3 Al 5 O 12 (YAG) (T m = 1827°C) and B 4 C-TiB 2 (T m = 2310°C) eutectic compositions were melted in a multimode 2.45GHz microwave furnace using a specially designed insulating package based on boron nitride. Our experiments demonstrate the stability of eutectic melt temperature (the absence of temperature runaway) and the uniformity of subsequent eutectic microstructure across the sample diameter during the re-solidification of big ~7cm 3 samples. The ability to reach ultra-high temperatures (T ~ 2400°C) and prevent the formation of significant thermal gradient across the sample confirms the potential of using microwave energy for processing of directionally solidified refractory ceramic eutectic compositions. INTRODUCTION Directionally solidified eutectics (DSEs) of oxide and non-oxide ceramic compositions are attractive composite materials due to their unique thermodynamic, mechanical and electrical properties 1 . In general these materials have excellent thermal stability, high-temperature strength and fracture toughness, which make them attractive candidates for ultra-high temperature structural materials 2 . In addition to their outstanding mechanical properties, some of the DSE compositions of rare-earth, alkali-earth and d-transition metal borides possess other exceptional properties such as high-electron emission, high neutron absorption ability, and specific magnetic and electrical characteristics 3 . The low thermal gradient across a sample and good temperature control during the re- solidification are critical factors for processing the high-quality eutectic rods with a diameter higher than 1 centimeter. Currently, there are several methods for fabricating DSEs, which can be divided into two main classes based on their process heat propagation scheme. The first class incorporates methods in which the heat is generated by an external source and propagates from the surface to the center of the ceramic rod. This class includes heating in a conventional resistive furnace 4 , inductive heating with an external susceptor 5 , infrared heating by halogen or xenon lamps 6 , laser beam heating 7 , and heating by electric arc or by electron beam bombardment 8 . In most instances, the ceramic rod is a sintered rod of ceramic powders of the desired eutectic composition. The main drawback of all of these methods is the presence of a thermal gradient within the rod, which may lead to an inhomogeneity of microstructure and restrict the sample diameter. The other class of melting techniques incorporates methods in which the heat is generated directly inside the sample, minimizing the formation of thermal gradients and potentially allowing for scaling to larger sample rods. One of the representatives of this class is inductive heating of conductive materials without an external susceptor 9 . In spite of