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Alloying in an Immiscible Cu-Nb System upon Solid-State Reaction

Published online by Cambridge University Press:  21 February 2011

F. Pan
Affiliation:
Currently on leave at Louisiana State University, Department of Mechanical Engineering, Baton Rouge, LA70803
Z.F. Ling
Affiliation:
Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
K.Y. Gao
Affiliation:
Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
B.X. Liu
Affiliation:
Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
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Abstract

In an immiscible Cu-Nb system, an amorphous alloy and two metastable crystalline phases were obtained by solid-state reaction of Cu-Nb multilayered films, and the formation of the alloy phases was found to be quite sensitive to the average composition of the films. At Nb concentration of 75at%, amorphization was achieved by 250°C annealing for 50 min, while in the films with compositions of 70 and 80 at% Nb, a simple cubic (a=0.405±0.005nm) and an orthorhombic phase (a=0.421, b=0.334, c=0.291±0.005nm) were observed, respectively. Thermodynamic calculation was conducted for the Nb-Cu alloy phases and the energetic state of the multilayers, which consisted of 9 Cu/Nb bilayers. It turned out that the excess free energy originating from the interfacial atoms could raise the multilayers to an energy level being higher than that of the amorphous or/and metastable crystalline phases both with a convex shape, and thus provided a major driving force for alloy phase formation in such immiscible system.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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References

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