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Metastable phase formation by ion mixing of Nb–Al multilayers

Published online by Cambridge University Press:  31 January 2011

K. Pampus
Affiliation:
Institute of Physics, University of Aarhus, DK-8000 Aarhus C, Denmark
K. Dyrbye
Affiliation:
Institute of Physics, University of Aarhus, DK-8000 Aarhus C, Denmark
B. Torp
Affiliation:
Institute of Physics, University of Aarhus, DK-8000 Aarhus C, Denmark
R. Bormann
Affiliation:
Institut für Metallphysik, Universität Göttingen, Hospitalstr. 3-5, D-3400 Göttingen, Federal Republic of Germany
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Abstract

The structure of Nb–Al thin films after ion mixing was studied for compositions from 20 to 85 at. % Al as a function of temperature in the range between 40 and 620 K. The phase formation was determined by transmission electron microscopy. At lower temperatures, only supersaturated bcc-solid solution, NbAl, and amorphous phase were found throughout the studied composition range. Besides these phases irradiation at temperatures above 470 K causes the formation of a metastable crystalline compound at an overall composition close to Nb25Al75, and for T = 623 K the equilibrium compound NbAl3 is formed. The other intermetallic phases Nb2Al and Nb3Al have not been observed at any irradiation temperature. Calculations of the Gibbs free energies of the various phases are presented, and the reliability of extrapolations to regions of metastability with respect to temperature and composition is commented on. The phase formation during heavy-ion irradiation is discussed in the context of the calculated free energies and kinetic constraints. For temperatures above 300 K, the attainment of a metastable phase equilibrium between the bcc solid solution and the amorphous phase is proposed due to the influence of radiation enhanced diffusion.

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Articles
Copyright
Copyright © Materials Research Society 1989

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