Modeling evaluation of Arrhenius factor and thermal conductivity for combustion synthesis of transition metal aluminides

Abstract

Two important rate-governing parameters, Arrhenius factor and thermal conductivity, in the process of combustion synthesis are numerically evaluated for the formation of transition metal aluminides, NiAl and CoAl. Correlation of the effective thermal conductivity (keff) with sample compaction density and dependence of the Arrhenius factor (K0) on the grain size of the reactant powders were established. Experimental data employed to validate the numerical model were obtained from the sample compacts composed of reactant powders with different grain sizes (Ni: <45 and 3–7 μm, Al: <40 and 10 μm, and Co: <45 μm) and formed by different densities (50%–70% TMD). For the Ni–Al samples of 50%–65% TMD, the calculated combustion velocity and temperature based upon keff/kbulk = 0.016–0.052 and K0 = 3.0 × 108–2.0 × 109 s−1 are in good agreement with those experimentally measured. The magnitudes of keff/kbulk = 0.028–0.08 and K0 = 1.5 × 108–4.0 × 108 s−1 were justified for combustion synthesis of CoAl from elemental powder compacts of 55%–70% TMD.