A study of mechanical alloying processes using reactive milling and discrete element modeling

The milling progress of mechanical alloying in SPEX shaker mills was investigated using different ball sizes and ball to powder mass ratios (charge ratios). Reactive materials were used, for which an exothermic reaction is mechanically triggered after a certain period of milling. The milling progress was determined experimentally from the temperature trace of the milling vial exhibiting a peak at the time of such a reaction. An expression for the milling dose was introduced to describe the effect of different milling parameters on the milling progress. In the first approximation, the milling dose leading to the mechanically triggered reaction remained constant over a range of charge ratios and could, therefore, be used to gauge the milling progress. The milling progress was described theoretically using the discrete element method. The theoretical milling dose that correlates well with its experimental analog was found to depend on the head-on impact energy dissipation rate. The presented approach is suitable for scale-up and optimization of mechanical alloying of various materials.