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Alloying of Cubic Alloys Based on Al3Ti: Phase Instabilities and the Control of Fault Energies

Published online by Cambridge University Press:  22 February 2011

David G. Morris ,
Reto Lerf  and
Mireille Leboeuf
David G. Morris
Affiliation:
Institute of Structural Metallurgy, University of Neuchâtel, 2000 Neuchâtel, Switzerland.
Reto Lerf
Affiliation:
Institute of Structural Metallurgy, University of Neuchâtel, 2000 Neuchâtel, Switzerland.
Mireille Leboeuf
Affiliation:
Institute of Structural Metallurgy, University of Neuchâtel, 2000 Neuchâtel, Switzerland.
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Abstract

Alloys based on Al3Ti with the ordered L12 structure show slight ductility when the Ti content is near 25% and about 8% of Mn or Cr is present as ternary addition. Such materials are relatively soft due to the easy movement of APB-dissociated superdislocations but remain almost completely brittle. While the precise reasons for such brittleness are not clear, it seems reasonable to consider that alloying to lower fault energies may soften the material and enhance ductility. In the present study, new alloys are selected on the basis of electronic structure calculations using the discrete variational cluster method, and the ordered state, mechanical behaviour, and dislocation and fault characteristics examined.

The alloys examined were based on the Al-26%Ti-8%Mn composition, with lower Ti and Mn contents, in an attempt to maintain a single-phase matrix and weaker, less-directional bonding and lower fault energies. In addition, for some alloys, Al was partially substituted by Mg.

The single-phase region of the L12 Al-Ti-Mn phase is very small and second phases such as DO22 and complex AlxMn can appear which lead to hardening and strain ageing, much as Al2Ti does in more Ti-rich alloys. Mg substitution is limited to a few percent before a Mg-rich phase appears and the alloys examined are complex mixtures of this, the L12 phase, and γTiAl. The dislocation structures observed after deformation are examined to determine fault energies, and it is shown that these values can be rationalised in terms of the structural instabilities of the matrix phases and the secondary phases produced.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 364: Symposium L – High-Temperature Ordered Intermetallic Alloys–VI , 1994 , 1215
Copyright
Copyright © Materials Research Society 1995

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