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 d ifferent 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, w hile milling at 473 K led to a fully decomposed, two-phase mixture. Pa rtially decomposed systems were obtained during milling at intermediat e temperatures with three co-existing phases all present. The milling- induced decomposition process had a very low apparent activation entha lpy, approximate to 0.11 eV, which is attributed to a first-order kine tic process involving non-equilibrium vacancies. The results are discu ssed in terms of competing mixing and de-mixing reaction rates.