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The influence of milling intensity on mechanical alloying

Abstract:

The frequency of vibration of the mill affects directly the milling intensity and therefore the ball to powder impact energy, this parameter has an influence on the alloy formation and on the particle size. In this work we have modified a Wig-L-Bug Spex mill in order to control the vibrating frequency. These results are compared with those obtained for the same milling periods with different ball size and also with milling in a conventional horizontal Wig-L-Bug and in a Spex 8000. The ball to powder ratio was kept constant for all the cases at 8:1. The ball motion was studied by observation with a high speed video camara through a transparent vial and the ball velocity calculated. The impact energy (the kinetic energy transfer to the powder at each collision event) was calculated and the vial frequency was changed to cover a significant impact energy range. Specific relations between vial frequency, impact velocity, impact energy, alloy formation and particle size with milling time were deduced. The materials were characterized by X-ray diffraction, and scanning electron microscopy for each milling condition. The milling periods were between 15 min and 5 h. The particle size and alloy formation depended strongly on the impact energy. Nanometer particle size and complete alloy formation were reached in shorter periods for higher intensities, for long periods the particle size was not affected by milling intensity.