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Phase Equilibria in the Ternary Nb-Cr-Al System and Site Occupation in the Hexagonal C14 Laves Phase Nb(AlxCr1-x)2

Published online by Cambridge University Press:  01 February 2011

Oleg Prymak ,
Frank Stein ,
Alexander Kerkau ,
Alim Ormeci ,
Guido Michael Kreiner ,
Georg Frommeyer  and
Dierk Raabe
Oleg Prymak
Affiliation:
o.prymak@mpie.de, Max-Planck-Institut fuer Eisenforschung, Duesseldorf, Germany
Frank Stein
Affiliation:
stein@mpie.de, Max-Planck-Institut fuer Eisenforschung, Duesseldorf, Germany
Alexander Kerkau
Affiliation:
Alexander.Kerkau@cpfs.mpg.de, Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden, Germany
Alim Ormeci
Affiliation:
ormeci@cpfs.mpg.de, Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden, Germany
Guido Michael Kreiner
Affiliation:
kreiner@cpfs.mpg.de, Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden, Germany
Georg Frommeyer
Affiliation:
frommeyer@mpie.de, Max-Planck-Institut fuer Eisenforschung, Duesseldorf, Germany
Dierk Raabe
Affiliation:
d.raabe@mpie.de, Max-Planck-Institut fuer Eisenforschung, Duesseldorf, Germany
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Abstract

The ternary Nb-Cr-Al phase diagram exhibits extended phase fields of the cubic C15 and the hexagonal C14 Laves phases Nb(AlxCr1-x)2. A number of Nb-Cr-Al alloys were prepared by levitation melting and annealed at temperatures between 1150 and 1450 °C for up to 1500 h. Isothermal sections of the ternary Nb-Cr-Al phase diagram at 1150, 1300 and 1450 °C were obtained from electron probe microanalysis, X-ray powder diffraction and metallographic investigations in order to study the effect of Al on the stability and structure of the Laves phases. The C14 Laves phase in the Nb-Cr-Al system can dissolve up to 45 at.% Al by substituting Cr with Al on the two different crystallographic B-sites 2a and 6h of the C14 AB2 unit cell. The site occupations of the Al and Cr atoms on these two B-sites were determined by Rietveld analysis using the program FullProf. The experimental site occupation factors were compared to site occupation factors computed by a statistical mechanics approach based on first-principles electronic structure calculations. The experimental as well as the calculated site occupation factors indicate a preferred occupation of the 2a site by Al.

Keywords

Nbphase equilibriax-ray diffraction (XRD)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1128: Symposium U – Advanced Intermetallic-Based Alloys for Extreme Environment and Energy Applications , 2008 , 1128-U08-11
Copyright
Copyright © Materials Research Society 2009

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References

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