Combustion Synthesis of High-Energy Ball-Milled Nb + 3Al Powder Mixtures

A major concern on making products by combustion reactions is to obtain high densities. In this work the combustion synthesis of Nb + 3Al powder mixtures is investigated with emphasis on densification behaviour. Two sets of mixtures were compared: high-energy ball-milled and simple mixtures. Milling was conducted on a vibratory mill at different times, to promote a highly refined dispersion of aluminum and niobium powders, avoiding in situ reaction. Cylindrical pellets were obtained by uniaxial compaction and reacted by thermal explosion mode under vacuum. Besides milling time, green density, degassing procedures and heating rates were also varied. Reacted pellets of NbAl3 were characterized in terms of final density, geometrical distortion and phases present in the microstructure. The results shown a great dependence of final density on milling time and that is possible to attain dense pellets with little dimensional distortion as compared to the ones from non-milled mixtures.