Precipitation mechanism in Ag–8 wt.% Cu alloy

The cellular precipitation in Ag–8 wt.% Cu alloy has been studied using dilatometric analysis, differential scanning calorimetriy, optical microscopy and X-ray diffraction (XRD). Dilatometric curve presents at ∼300 °C an anomaly identical to that representing an allotropic transformation, which means a formation of a new crystallographic structure. Thus the ageing temperature can affect the initiation mechanism of the reaction. At low temperature thermal migration of grain boundaries and cells formation precede boundary precipitation. At high temperature the structure consists of alternate lamellar of the α (Ag-rich) – solid solution and β (Cu-rich) – solid solution phases. The activation energy Eact equals to 56.5 ± 6.2 kJ/mol at low temperature (196 °C) and to 109.5 ± 6.7 kJ/mol at high temperature (300 °C).