Formation of Intermetallic-Ceramic Composites from Nanoreactants in a Self-Sustaining Reaction Regime
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Formation of Intermetallic-Ceramic Composites from Nanoreactants in a Self-Sustaining Reaction Regime Shivanee R. Dargar; Lori J. Groven; Jacek J. Swiatkiewicz; and Jan A. Puszynski Chemistry and Chemical Engineering Department South Dakota School of Mines and Technology 501 East Saint Joseph Street Rapid City, SD 57701, U.S.A ABSTRACT Processing of nanoreactant energetic system, Al-TiO2, in the thermal explosion mode of combustion synthesis was investigated. Simultaneous combustion synthesis and densification experiments were carried out in a uniaxial press to obtain homogeneous as well as functionally graded products of the above reactant system. It was demonstrated that TiAl3-Al2O3 composite product synthesized from Al-TiO2 reactant system retained its sub-microstructure despite a short term exposure to higher temperatures. Composite materials with densities of 96-98% of the theoretical densities were obtained. The effect of several key processing parameters such as initial composition of reactants and temperature-pressure conditions on morphology of combustion synthesized product, their phase composition, and residual porosity were investigated. DSC, XRD, SEM, and LIBS analyses were used to characterize both reactants and products. INTRODUCTION Combustion synthesis has been found to be an effective and economical processing technique for synthesis of advanced ceramic and intermetallic compounds [1-4]. Traditional consolidation techniques, such as high temperature pressureless sintering and hot pressing, have several limitations, including high cost, low throughput, and long exposure to high temperatures, which result in dense products with relatively large grain sizes. In order to reduce the average grain size of sintered materials two important factors must be met: i) nano-size of starting powders and ii) low sintering temperature. Many metals and ceramic powders sinter at much lower temperatures if the average particle size is in the range of a few nanometers [5-9]. Therefore, the use of nanoreactants is a key parameter in retaining the product nanostructure and achieving product densities as close to theoretical density as possible. In the present investigation the utilization of the combustion synthesis process with nanoreactants and in-situ densification allows processing of the hot and ductile products to achieve high density, nanostructured end products. EXPERIMENTAL PROCEDURE The following raw materials were used for synthesis: 1) aluminum powder from Technanogy Company (davg=50 nm); 2) titanium dioxide from Degussa Corporation (davg=40 nm). Wet mixing technique was used to mix the nanoreactants and is described in detail elsewhere [8]. In-situ combustion synthesis and densification experiments were performed, in argon, in the equipment depicted in Figure 1, with varying uniaxial pressure conditions: no
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pressure, 100 MPa uniaxial pressure before ignition, and 100 MPa at ignition. The system has a preheating capability up to 1500K and densification pressures up to 200 MPa. In addition,
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