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Surface segregation in a dilute copper–silver alloy

Published online by Cambridge University Press:  31 January 2011

S.W. Bronner  and
P. Wynblatt
S.W. Bronner
Affiliation:
Department of Metallurgical Engineering and Materials Science, Carnegie–Mellon University, Pittsburgh, Pennsylvania 15213
P. Wynblatt
Affiliation:
Department of Metallurgical Engineering and Materials Science, Carnegie–Mellon University, Pittsburgh, Pennsylvania 15213
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Abstract

The equilibrium surface composition of a Cu-0.83 at. % Ag alloy has been studied over the range from 600°–400°C. Above 450°C the alloy consists of a single phase, whereas below that temperature the material separates into copper-rich and silver-rich phases. The kinetics of equilibration appear to be controlled by grain boundary diffusion, leading to more rapid equilibration than expected on the basis of lattice diffusion-controlled kinetics. In the single-phase regime, silver segregates to the surface with an average enthalpy of segregation of −24 kJ/mol and an entropy of segregation of 0.94 J/mol K, and displays a trend of increasing equilibrium silver surface concentration with decreasing temperature. Theoretical estimates of the enthalpy of segregation yield the somewhat more negative values of −60 and −47 kJ/mol, respectively. In the two-phase regime, the surface continues to be enriched in silver, but the silver surface concentration decreases with decreasing temperature as a result of the rapidly decreasing equilibrium solubility of silver in copper.

Type
Articles
Information
Journal of Materials Research , Volume 1 , Issue 5 , October 1986 , pp. 646 - 651
Copyright
Copyright © Materials Research Society 1986

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References

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