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Effect of B Addition on Thermal Stability of Lamellar Structure in Ti-47Al-2Cr-2Nb Alloys

Published online by Cambridge University Press:  26 February 2011

Y. Yamamoto ,
N. D. Evans ,
P. J. Maziasz  and
C. T. Liu
Y. Yamamoto
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN37831, U.S.A
N. D. Evans
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN37831, U.S.A
P. J. Maziasz
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN37831, U.S.A
C. T. Liu
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN37831, U.S.A
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Abstract

Thermal stability of fully lamellar microstructures in Ti-47Al-2Cr-2Nb (at.%) alloys with and without B additions has been evaluated in the temperature range of 800 to 1200°C. The alloy with 0.15B exhibits an α2 + γ fully lamellar microstructure containing ribbon-like structures (TiB2+β) inside the lamellar colonies. During aging at 800 and 1000°C, β particles surrounded by γ grains form adjacent to the ribbon-like structures. The formation of these grains is attributed to the precipitation of thin plate-like β phase along {1100} within the TiB2 ribbon particles, resulting in the loss of α2 plates around the ribbon-like structure by scavenging Ti. This allows coarsening γ lamellar plates to form new γ grains, and then the ribbon-like structure completely dissolves to leave only β particles. At 1200°C, discontinuous coarsening (DC) of the lamellae becomes the dominant mode of microstructural change for all the alloys. However, the ribbon-like structures in the alloy with B additions play a role in pinning the DC cells, which leads to higher thermal stability of the lamellar microstructure in that alloy.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 842: Symposium S – Integrative and Interdisciplinary Aspects of Intermetallics , 2004 , S6.8
Copyright
Copyright © Materials Research Society 2005

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References

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