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Electronic bonding characteristics of hydrogen in bcc iron: Part II. Grain boundaries

Published online by Cambridge University Press:  31 January 2011

Yoshio Itsumi  and
D.E. Ellis
Yoshio Itsumi
Affiliation:
Materials Research Laboratory, Kobe Steel, Ltd., Japan
D.E. Ellis
Affiliation:
Department of Physics and Astronomy and Materials Research Center, Northwestern University, Evanston, Illinois 60208
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Abstract

Electronic structure calculations were carried out for bcc iron grain boundaries (GB) with or without hydrogen, using the self-consistent Discrete Variational embedded cluster method within the first-principles local density formalism. Bonding characteristics were mainly investigated. Simple rigid body translations perpendicular to the GB plane were used for estimation of relaxed GB geometry. Analysis of bond order summation over the GB shows considerable volume expansion normal to the GB plane of a dense 23(111) twist/tilt GB and some compression for the rather open 23(110) twist configuration. These results are discussed in the context of atomistic simulations which suggest that higher energy GB's generally have larger volume expansion normal to the GB plane. H in a 23(111) GB reduces Fe-Fe bonding strength by —3% within a 0.25 nm spherical volume around the H site, associated with reduction of the 4s and 4p occupancy of the nearest neighbor Fe. Since these orbitals contribute mainly to metallic bonding, the action of H atoms as an embrittlement inducer can be understood.

Type
Articles
Information
Journal of Materials Research , Volume 11 , Issue 9 , September 1996 , pp. 2214 - 2219
Copyright
Copyright © Materials Research Society 1996

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References

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