27Al Nuclear Magnetic Resonance Analysis of Mechanical Alloy ing Process in Cu－Al Mixed Powders

Abstract

Pure elemental powders of copper and aluminum with particle size 200 mesh (75 μ m) were weighted and mixed to give the desired average composition of Cu15 Al 85 (at.%). The variations of the 27 Al nuclear magnetic resonance (NMR) spectra have been measured for the powder mixtures after different times of ball milling. By analyzing the 27 Al NMR spectra, through the comparison with the earlier reports, the detailed physical discussion has proceeded based on the elemental principles of NMR and the process of mechanical alloying (MA) on an atomic scale has been investigated. With increasing the ball milling time, 27 Al Knight shifts in the series of Cu 15 Al 85 samples decrease from 0.164% to 0.158%. This means that the states of valence electrons have been altered and the s like component of the conduction electrons reduced. The chemical short ranged order (CSRO) near the 27 Al nuclei is changed significantly. The formation and development of the alloyed clusters having various CSRO are caused by a strong interaction, on an atomic scale, between copper and aluminum in the mixtures during the milling processing. The strong interactions among the valence electrons of Cu and Al cause the changes in wavefunctions. The experimental results indicate that the true alloying reaction takes place during the ball milling process, and it completes after about 90 hours of ball milling on our mechanical alloying conditions. Moreover, the CSRO in the samples prepared by MA are the same as those with the ingredients prepared by melting.