(657b) Experimental Indicators of Materials Processing Progress In Mechanical Alloying and Reactive Milling

Mechanical milling is widely explored to prepare advanced alloyed and composite materials.  However, it is often unclear how to transfer production from small scale laboratory mills to larger scale devices for practical manufacture of the desired materials.  Recently, a simplified approach was proposed, in which the rates of energy transfer to the material from milling tools were calculated for three different mills using discrete element modeling (DEM); these rates were correlated with the averaged experimental rates of increase in the yield strength of an oxide reinforced composite as a function of its milling time.  The results were encouraging, but two significant limitations remained.  First, experimental validations relied on tangible changes in the yield strength of the milled material.  Such changes, common for oxide reinforced composites, could be less pronounced or insignificant for other materials.  Second, a steady-state refinement was assumed.  The latter assumption needs to be revisited if restitution and friction coefficients change during milling, resulting in altered rates of energy transfer from milling tools to the powder.  Therefore, one of the goals of this effort is to enable a validation of the DEM calculations for materials, for which measurements of yield strength are impractical.  The second goal is to develop real-time indicators of milling progress achieved in an attritor mill, which do not require recovery of the powder samples.  The utility of such real-time indicators is two-fold.  First, no labor-intensive recovery and examination of the partially milled powders is required.  Second, the instantaneous changes in the powder properties, affecting friction and restitution coefficients can be accounted for in modified DEM calculations.  The attritor mill is specifically selected for this study as the device most suitable for large scale manufacturing of mechanically milled materials.  Correlations between the rate of power consumption, torque, and rpm of the motor and the powder refinement are examined.  Yield strength measurements for the recovered samples are correlated with changes in the measured x-ray diffraction patterns.