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First principles calculation of the elastic constants of intermetallic compounds: metastable Al3Li

Published online by Cambridge University Press:  31 January 2011

X-Q. Guo ,
R. Podloucky  and
A.J. Freeman
X-Q. Guo
Affiliation:
Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208
R. Podloucky
Affiliation:
Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208
A.J. Freeman
Affiliation:
Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208
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Abstract

We report first principles local density calculations for the metastable Al3Li intermetallic compound with cubic L12 crystal structure using the full-potential linearized augmented plane wave method. From the second derivative of the total energy as a function of volume, and generated tetragonal and trigonal lattice distortions, the elastic constants C11, C12, and C44 were derived yielding C11 = 158 GPa, C12 = 29.4 GPa, and C44 = 57.7 GPa. Because of the very high Young's modulus (E = 141 GPa) compared, for example, to pure Al (E = 66 GPa), it is suggested that Al3Li plays an important role in strengthening the Al–Li alloys. The calculated Young's modulus appears in good agreement with experimental estimates when the experimental values are extrapolated to 0 K. Although the Young's modulus of Al3Li is increased in comparison to Al, the calculated bulk modulus is decreased to a value of 72 GPa as compared to pure Al (82 GPa), in agreement with experiment. As a result, the Poisson ratio is reduced to ŝ = 0.173 as compared to the value 1/3 for an isotropic medium. Because of this and the high Young's modulus, the calculated Debye temperature ΘD at 0 K amounts to 672 K, which is substantially larger than ΘD for Al, which is about 400 K.

Type
Articles
Information
Journal of Materials Research , Volume 6 , Issue 2 , February 1991 , pp. 324 - 329
Copyright
Copyright © Materials Research Society 1991

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