Precipitation Kinetics and Mechanism in Cu-7 wt% Ag Alloy

Djamel Hamana, Mohamed Hachouf, Leila Boumaza, Zine El Abidine Biskri
2011 Materials Sciences and Applications  
The discontinuous precipitation kinetics and mechanism of the  (Ag-rich) phase in Cu-7 wt% Ag alloy has been investigated using dilatometric and calorimetric anisothermal analysis, optical microscopy, scanning and transmission electron microscopy and X-ray diffraction. Dilatometric and calorimetric curves present at ~ 500˚C an important effect related to the  (Ag-rich) phase formation and consequently the matrix β (Cu-rich) depletion. The nucleation and growth of the precipitated phase show
more » ... itated phase show cells formation at initial grain boundaries; a fine lamellar structure is detected by SEM and TEM and consists of alternate lamellar of the α (Ag-rich) and β (Cu-rich)-solid solutions. Cellular precipitation leads to the simultaneous appearance of two diffraction peaks and occurs apparently according to the Fournelle and Clark's mechanism. Obtained results give an Avrami exponent n = 2.0 ± 0.2 in agreement with an interfacial controlled process having an activation energy E a equals to 99 ± 7 kJ/mol obtained from anisothermal analysis by using different isoconversion methods. This activation energy expresses the discrepancy between isoconversion methods and the analytical diffusive model. Moreover, the supersaturation rate has an effect on the lamella spacing of the precipitated cells. Figure 9. TEM micrograph of Cu-7 wt% Ag alloy aged at 400˚C for 15 min (a) and the corresponding analysis of the different areas (O 1 , O 2 , O 3 ,O 4 ) (b).
doi:10.4236/msa.2011.27120 fatcat:sbilkjimjbe6pkzpjvhin6tkye