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Phase Formation and Microstructural Development During Solid-State Reactions in Ti-Al Multilayer Films

Published online by Cambridge University Press:  15 February 2011

Carsten Michaelsen ,
Stefan Wöhlert  and
RÜdiger Bormann
Carsten Michaelsen
Affiliation:
Institute for Materials Research, GKSS Research Center, D-21502 Geesthacht, Germany
Stefan Wöhlert
Affiliation:
Institute for Materials Research, GKSS Research Center, D-21502 Geesthacht, Germany
RÜdiger Bormann
Affiliation:
Institute for Materials Research, GKSS Research Center, D-21502 Geesthacht, Germany
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Abstract

The phase selection which is generally observed in the early stages of solid-state reactions was studied using Ti-Al multilayer films as a model system.

Although all Ti-Al intermetallic phases have similar driving forces of about 30 kJ/g-atom, TiAl3 is the only phase which is formed as long as the reactants are not consumed. The critical thickness beyond which a second phase is formed is larger than 100 μm. We found that the formation of TiAl3 takes place by nucleation and growth, demonstrating that the driving force available for first-phase formation is considerably reduced by a preceding formation of solid solutions. Furthermore, we observed that nucleation continues at later stages, indicating that non-equilibrium conditions are maintained which are possibly influenced by grain-boundary diffusion. However, the phase selection is determined by the different growth velocities, being much higher for TiAl3 than for all other phases.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 343: Symposium H – Polycrystalline Thin Films - Structure, Texture, Properties and Applications , 1994 , 205
Copyright
Copyright © Materials Research Society 1994

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References

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