Characterization of Co-Cu mechanical alloys by linear sweep voltammetry

The mechanical alloying process has shown that it is possible to obtain supersaturated solid solutions at any composition in immiscible metallic systems by ball milling of elemental powder mixtures. The mechanically alloyed Co-Cu powders are chemically homogeneous supersaturated solid solutions and exhibit crystallite sizes of a nanometer order. In the present work, the mechanically alloyed Co-Cu powders have been characterized by linear sweep voltammetry in 0.5 M NaOH and 0.15 M Na2B4O7 aqueous solutions. The electrochemical behavior has been related to the characteristics of enhanced solubility found in Co-Cu mechanical alloys. In order to perform a systematic study of this system, the voltammograms of pure Cu, pure Co, Co-Cu original powder mixtures and Co-Cu alloys, obtained by melting and casting, were also analyzed for comparison. The results showed that the voltammograms of mechanically alloyed Co-Cu powders presented peaks of dissolution at potentials intermediate between those exhibited in pure Cu and Co samples. Moreover, a third dissolution peak occurred at more noble potentials in mechanical alloys, but not in as-cast alloys. This peak is associated with the formation of the solid solution, in mechanical alloys. This suggests that both elements are dissolved simultaneously, which confirms that Co-Cu mechanical alloys are true supersaturated solid solutions. Additionally, it was found that the MA Co-Cu alloys showed corrosion rates higher than those in as-cast alloys, which is attributed to the high value of stored energy presented in MA alloys as a result of the severe plastic deformation during ball milling. Copyright (C) 1996 Elsevier Science Ltd