Mechanical alloying process of Cu-Zn system studied by 63Cu nuclear magnetic resonance

The process of mechanical alloying (MA) and the phase transformations that accompany ball milling the elemental Cu and Zn powder mixtures have been investigated by 63Cu nuclear magnetic resonance spectrometry and x-ray diffractometry. The 63Cu Knight shifts in mechanically alloyed clusters of α, β, γ, or ε phases show significantly different from that of heavily deformed pure copper, indicating a reduction of s-like electron density. The wave functions around the Cu atoms are likely to assume a greater ‘‘p’’ character when Zn is added. The formation and development of alloyed clusters are caused by the strong bonding interactions between Cu and Zn when the mixtures are ball milled. Under present conditions the alloying reaction is accomplished after milling about 15 h for Cu-39 at. % Zn, and it is faster when the Zn content is smaller. No amorphous phase was detected in the Cu-Zn system. The local atom rearrangement in the alloyed clusters is facilitated by the onset of the internal stress induced by MA. This might prevent the retaining of amorphous phase even if partial amorphization may occur during the MA process.