Mechanical alloying of immiscible elements: experimental results on Ag-Cu and Co-Cu

Equimolar solid solutions of Ag-Cu and Co-Cu were prepared by mechanical milling of the elements. The structure and the thermodynamic properties of the resulting phases were analysed by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Large mixing enthalpies (Delta H = 6.8 kJ g-atom(-1) and Delta H = 4.8 kJ g-atom(-1) for Ag-Cu and Co-Cu respectively) were measured in the alloyed phases. It is clear that the solid solution forms through a process of grain refinement down to the nanometre scale and is assisted by an atomic-scale dissolution. The possible role played by coherent interfaces in substantially increasing the energy of the solid solutions is discussed.