THE INFLUENCE OF THE REACTANT SIZE ON THE MICROPYRETIC SYNTHESIS OF NIAL INTERMETALLIC COMPOUNDS

The effect of the nickel (Ni) and aluminum (Al) reactant particle size on the micropyretic synthesis of NiAl is studied in this article. A change in the low melting component (Al particle) size is noted to have a limited influence on the micropyretic synthesis conditions. However, a change in the high melting component (Ni particle) size not only influences the combustion temperature and propagation velocity, but also affects the final porosity and grain size of the synthesized products. The combustion mode is also noted to change from stable to unstable when the Ni particle size is increased. It is noted that a diffusion-type control mechanism is dominant for the rapid reaction sequence in the NiAl system. An atomistic mechanism of the Ni-Al micropyretic reaction is also proposed in this article. Following this model, analytical expressions are developed to relate the variation of the Ni size to the NiAl formation rate with the imposed processing conditions during the micropyretic synthesis. The mechanism of the final grain formation and the grain size changes with changes in the processing variables is also discussed.