Ball milling of systems with positive heat of mixing: Effect of temperature in Ag-Cu

Ag50Cu50 alloys prepared by ball milling were subsequently milled at different temperatures ranging from about 85 to 473 K and investigated by X-ray diffraction and differential scanning calorimetry. Milling at subambient temperatures led to a homogeneous f.c.c. solid solution, while milling at 473 K led to a fully decomposed, two-phase mixture. Partially decomposed systems were obtained during milling at intermediate temperatures with three co-existing phases all present. The milling-induced decomposition process had a very low apparent activation enthalpy, approximate to 0.11 eV, which is attributed to a first-order kinetic process involving non-equilibrium vacancies. The results are discussed in terms of competing mixing and de-mixing reaction rates.