The effect of high energy ball milling on the mixing behaviour of binary systems which do not show any intermediate phase in the equilibrium phase diagram owing to their positive enthalpy of mixing has been studied by Transmission Electron Microscopy on equiatomic mixtures submitted to short term high energy milling. Previous experimental results on the Cu-Fe and on the Ag-Fe systems showed that a possible reaction mechanism can be based on the mutual interdiffusion in some steps of the ball milling process and on partial or total decomposition of the metastable solid solution during some other steps. However the experimental evidences were far from being conclusive. In this paper we report further experimental results concerning the Ag-Cu system. TEM analyses show that practically no alloying between Ag and Cu is observed after short term milling, while the orientation relationships between adjacent crystals of Cu and Ag suggest the transient presence of a metastable solid solution. This behaviour is discussed and compared with the Cu-Fe system where, on the contrary, a noticeable solid state alloying is observed also after short term milling.

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