Al-27 nuclear magnetic resonance analysis of mechanical alloying process in Cu-Al mixed powders

The variations of the Al-27 nuclear magnetic resonance (NMR) spectra of the aluminum-copper powder mixtures after different time of ball milling have been measured. By analyzing the Al-27 NMR spectra, the mechanical alloying (MA) process has been investigated at microscopic level. Al-27 Knight shift s in the series of Cu-Al samples decrease with increasing time of ball-mill ing. This means that the s component in the states of valence electron decl ines. The experimental results indicate that the ture alloying reaction tak es place during the MA process, and it is complete after about 90 hours of ball milling under our mechanical alloying conditions. Compared with the ea rly results of Al-27 Knight shifts measured in the samples prepared by the traditional melt-alloying method, it has been concluded that the real Cu-Al alloys can be obtained by MA process, and they possess the same chemical s hort-ranged order as those with the same ingredients obtained by melting.