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Interface Structure and Energy Calculations for Carbide Precipitates in γ-TiAl

Published online by Cambridge University Press:  11 February 2011

R. Benedek ,
D. N. Seidman  and
C. Woodward
R. Benedek
Affiliation:
Materials Science and Engineering Department, Northwestern University, Evanston, Il 60208
D. N. Seidman
Affiliation:
Materials Science and Engineering Department, Northwestern University, Evanston, Il 60208
C. Woodward
Affiliation:
Materials Science and Engineering Department, Northwestern University, Evanston, Il 60208 Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright Patterson AFB, OH, 45433–7817, November 22, 2002
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Abstract

Ternary carbide precipitates improve the high-temperature creep strength of 2-phase TiAl alloys. The perovskite (P-type) Ti3 AlC nucleates at relatively low temperatures (750 deg. C), whereas hexagonal (H-type) Ti2AlC precipitates occur at somewhat higher temperatures. Calculations are performed, based on first- principles-local-density-functional theory, of the interface structure and energy of these two carbides with a 7-TiAl matrix. Calculations are first done on coherent interfaces, and approximate corrections are then made for the effect of misfit. The perovskite is known to form needle-shaped precipitates oriented along the c-axis of the host. Our calculations yield a relatively low energy for the (100) perovskite-host interface, which is a favorable orientation owing to its low misfit, and because the terminating carbide layer for the coherent interface is pseudomorphic with the host. Predictions are given for the critical thickness for coherence and the critical nucleation size for a P-type precipitate. Calculations for interfaces of H-type platelets with the host show a much larger interface energy than that for the P-type precipitate.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 753: Symposium BB – Defect Properties and Related Phenomena in Intermetallic Alloys , 2002 , BB3.5
Copyright
Copyright © Materials Research Society 2003

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