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Solute-Atom Segregation and Two-Dimensional Phases at Internal Interfaces: Atomic Resolution Observations

Published online by Cambridge University Press:  26 February 2011

Roman Herschitz ,
David N. Seidman  and
Avner Brokman
Roman Herschitz
Affiliation:
R.C.A. Inc., Astroelectronics Division, Princeton, NJ 08540
David N. Seidman
Affiliation:
Northwestern University, Department of Materials Science, Evanston, IL 60201-9990
Avner Brokman
Affiliation:
The Hebrew University, Graduate School of Applied Science, Jerusalem, Israel 91904
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Abstract

Solute-atom segregation effects to individual stacking faults (SFs) in Co-0.96 at.% Nb and Co-0.98 at.% Fe alloys were studied employing the atom-probe field-ion microscope (FIM) and transmission electron diffraction techniques. The mean composition of individual SFs was measured for bulk specimens which had been equilibrated in the range 450-575°C. In addition, the composition was measured with a spatial resolution, within the plane of the SFs, of ~1 Å and with a spatial resolution of <4 Å perpendicular to the SFs. These measurements demonstrated the following: (a) The meancompostion of the SFs increased with decreasing temperature according to an Arrhenius-like expression; (b) The Nb or Fe concentrations fall off very quickly with distance--within <4 Å from the plane of the SF the bulk concentation is achieved; (c) The SFs equilibrated above 4500 C contained solute-atom fluctuations (≈5 to 20 \ diameter) which correspond to compositions with stoichiometries of ≈Co2Nb or ≈Co3Fe. In the case of the Co(Nb) alloy, a transmission electron diffraction pattern was obtained ofa SF--with the electron beam normal to the SF--which exhibited superlattice reflections with six-fold symmetry around the hcp matrix reflections. This latter result is consistent with a two-dimensional phase in the SF plane with the composition Co2 Nb. Both the atom-probe FIM and the electron diffraction studies are consistent with two dimensional (2D) ordered phases in the SFs.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 82: Symposium I – Characterization of Defects in Materials , 1986 , 415
Copyright
Copyright © Materials Research Society 1987

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References

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