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

DOI: 10.4236/msa.2011.27120   PDF   HTML     4,375 Downloads   8,357 Views   Citations


The discontinuous precipitation kinetics and mechanism of the α (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 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 Ea 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.

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D. Hamana, M. Hachouf, L. Boumaza and Z. Biskri, "Precipitation Kinetics and Mechanism in Cu-7 wt% Ag Alloy," Materials Sciences and Applications, Vol. 2 No. 7, 2011, pp. 899-910. doi: 10.4236/msa.2011.27120.

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The authors declare no conflicts of interest.


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