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Positron Annihilation Spectroscopy and Small Angle Neutron Scattering Characterization of Nanostructural Features in Irradiated Fe-Cu-Mn Alloys

Published online by Cambridge University Press:  21 March 2011

B. D. Wirth ,
P. Asoka-Kumar ,
R. H. Howell ,
G. R. Odette  and
P. A. Sterne
B. D. Wirth
Affiliation:
Lawrence Livermore National Laboratory, Livermore, CA 94551
P. Asoka-Kumar
Affiliation:
Lawrence Livermore National Laboratory, Livermore, CA 94551
R. H. Howell
Affiliation:
Lawrence Livermore National Laboratory, Livermore, CA 94551
G. R. Odette
Affiliation:
University of California, Santa Barbara, Santa Barbara, CA 93106
P. A. Sterne
Affiliation:
Lawrence Livermore National Laboratory, Livermore, CA 94551
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Abstract

Radiation embrittlement of nuclear reactor pressure vessel steels results from a high number density of nanometer sized Cu-Mn-Ni rich precipitates (CRPs) and sub-nanometer matrix features, thought to be vacancy-solute cluster complexes (VSC). However, questions exist regarding both the composition of the precipitates and the defect character and composition of the matrix features. We present results of positron annihilation spectroscopy (PAS) and small angle neutron scattering (SANS) characterization of irradiated and thermally aged Fe-Cu and Fe-Cu-Mn alloys. These complementary techniques provide insight into the composition and character of both types of nanoscale features. The SANS measurements indicate populations of CRPs and VSCs in both alloys. The CRPs are coarser in the Fe-Cu alloy and the number densities of CRP and VSC increase with the addition of Mn. The PAS involved measuring both the positron lifetimes and the Doppler broadened annihilation spectra in the high momentum region to provide elemental sensitivity at the annihilation site. The spectra in Fe-Cu-Mn specimens thermally aged to peak hardness at 450°C and irradiated at 288°C are nearly identical to elemental Cu. Positron lifetime and spectrum measurements in Fe-Cu specimens irradiated at 288°C clearly show the existence of long lifetime (∼500 ps) open volume defects, which also contain Cu. Thus the SANS and PAS provide a self-consistent picture of nanostructures composed of CRPs and VSCs and tend to discount high Fe concentrations in the CRPs.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 650: Symposium R – Microstructural Processes in Irradiated Materials-2000 , 2000 , R6.5
Copyright
Copyright © Materials Research Society 2001

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References

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