Melting behavior and origin of strain in ball-milled nanocrystalline Al powders

Ball-milled aluminum powders have been investigated by differential scanning calorimetry and high resolution X-ray line profile analysis. Ball-milling was carried out for different milling times ranging from 45 min to 32 days. The milling time dependence of the average grain-size and of the density of lattice defects, mainly dislocations, were determined by the modified Williamson-Hall and Warren-Averbach procedures based on the dislocation model of mean square strain. Characteristic grain sizes of ball-milled Al-powders decreases with increasing milling time and simultaneously, the grain-size distribution becomes sharper. Calorimetric measurements indicated the decrease of the melting point, Tm with increasing milling time. The melting point depression was found to be proportional to inverse grain size. The strain accumulated in the powder particles is mainly caused by intergrain dislocations. C 2005 Springer Science + Business Media, Inc.