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Structural Energy Differences in Al3Ti: The Role of Tetragonal Distortion in APB and Twin Energies

Published online by Cambridge University Press:  26 February 2011

O. M. Nicholson ,
G. M. Stocks ,
W. M. Temmerman ,
P. Sterne  and
D. G. Pettifor
O. M. Nicholson
Affiliation:
Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6114
G. M. Stocks
Affiliation:
Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6114
W. M. Temmerman
Affiliation:
Daresbury Laboratory, SERC, Daresbury, Warrington WA4 4AD, England
P. Sterne
Affiliation:
University of Maryland, College Park, MD 20742
D. G. Pettifor
Affiliation:
Imperial College, Queen's Gate, London SW7 2BZ, England
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Abstract

At stoichiometry, DO22 is the observed ground state of Al2Ti and has a C/A ratio of 2.23, but as a function of both concentration and temperature other ordered arrangements of APB's are observed. These phase transitions have sparked many studies in which the energy has been treated as that of chemical rearrangement on an fcc lattice. We have found that at the ideal C/A ratio, the Ll2 structure is lower in energy, but as the tetragonal distortion increases the DO22 energy drops below that of Ll2. The critical role played by the tetragonal distortion in the balance between Ll2 and DO22 energies precludes the use of any model based on the undistorted lattice.

The major impediment to the development of Al3Ti as a high-temperature material is its lack of ductility. The standard approach is to make alloy additions which transform the structure to Ll2. An alternate approach is to work toward the enhancement of ductility in the DO22 phase. As a first step we have calculated the twinning energy in Al3Ti.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 133: Symposium H – High-Temperature Ordered Intermetallic Alloys III , 1988 , 17
Copyright
Copyright © Materials Research Society 1989

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References

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