Oxidation of Ti 3 SiC 2 composites in air
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I. INTRODUCTION
THE ternary ceramic Ti3SiC2 has a unique combination of metal-like properties, including excellent machinability, strength, ductility at high temperatures, low density, and high electrical and thermal conductivity. It is considered to be a promising candidate for high-temperature structural materials, such as turbine blades and stators. It can be a machinable substitute for superalloys and other high-temperature materials and is a promising candidate for ceramic engines. It is also believed to be a potential candidate for certain applications, such as bearings, which require lubricity at elevated temperatures in air and other oxidizing environments. Its good electrical-thermal conductivity and thermal shock resistance make it an ideal candidate for electrodes for metal smelting, in general, and especially in aluminum smelting.[1] Table I summarizes the various physical properties of phase-pure Ti3SiC2 synthesized from Ti, SiC, and graphite powders that were dry mixed, cold pressed, and hot isostatically pressed at 1600 ⬚C for 4 hours.[1] Because of the importance of Ti3SiC2, many different strategies have been examined as possible synthesis routes. A solid-state chemical reaction between TiH2, silicon, and graphite at 2273 K was first reported by Jeitschko and Nowotny[2] for synthesis of the ternary carbide. Vapor-phase chemical reactions between SiCl4, TiCl4, CCl4, and H2 have been shown to produce Ti3SiC2.[3] Arc melting and annealing of elemental Ti, Si, and C powders in an inert atmosphere or under vacuum is another valid route to synthesize bulk Ti3SiC2 with a small amount of TiC.[4] Self-propagating high-temperature synthesis (SHS) is reported to be a promising method for the synthesis of Ti3SiC2.[5] The SHS reaction typically occurs either via the thermal explosion or combustion mode.[6] In the thermal explosion mode (also called “reactive sintering,” “reaction,” T. CHEN, Engineer, is with Advanced Technologies, Delta Airlines, Inc., Atlanta, GA 30320-6001. P.M. GREEN, J.L. JORDAN, Graduate Research Assistants, J.M. HAMPIKIAN, Associate Professor, and N.N. THADHANI, Professor, are with the School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332. Contact e-mail: [email protected] Manuscript submitted April 23, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
or “volume combustion synthesis”), mixed powders are adiabatically heated in a furnace until the onset of reaction between the constituents. A bulk exothermic reaction is then spontaneously initiated through all parts of the reactants resulting in compound formation. The combustion mode of SHS refers to the ignition of a reaction at one end of a coldpressed green reactant containing the powder mixtures by a heat source (electric spark, hot tungsten wire, laser, or ion beam). This results in a self-propagating exothermic reaction propagating in the form of a combustion wave through the green reactant, leaving behind the synthesized product.[7,8] It has been shown that following combustion
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