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Mechanical alloying in the immiscible systems Ag-M (M = Fe, Co, Ni)

Abstract:

Mechanical alloying in binary systems immiscible in equilibrium, which are characterized by a large positive heat of mixing, has been a subject of considerable interest during the last two decades. The ball milling process being a non-equilibrium technique, which causes a high density of defects, seems promising in obtaining at least a partial solid solution in these systems. In this paper we present a comparative study about the systems Ag-Fe, Ag-Co and Ag-Ni. The phase diagrams of these systems show that the mutual solubility is very low in both the solid and liquid states. Therefore, no stable alloys of appreciable compositions exist under equilibrium conditions. However, it has been found that a prolonged and energetic ball milling can produce metastable alloys. We use the ideal solution (IS) model to make a thermodynamic study of these systems. This model pbkp_redicts that in spite of the high positive heat of mixing, the activation energy in these systems is small enough so that ball milling can provide the energy required to promote the formation of an unstable solid solution.