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Title:Positron annihilation spectroscopy to understand defect formation and evolution in neutron-irradiated Fe-Cr model alloys
Author(s):Romnes, Carly J.
Advisor(s):Stubbins, James F; Krogstad, Jessica A
Department / Program:Nuclear, Plasma, & Rad Engr
Discipline:Nuclear, Plasma, Radiolgc Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Positron annihilation spectroscopy, iron, chromium, neutron irradiation
Abstract:Positron annihilation spectroscopy (PAS) is a powerful, non-destructive technique used to characterize the defect properties of materials. There are two major types of PAS, positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy (DBS). This work focused on the latter. DBS can be used to gain information on the various types of defects present in a material system and this technique is sensitive to both defect size and defect concentration. Several samples were irradiated at the Advanced Test Reactor at Idaho National Laboratory. These samples were irradiated at temperatures of 300, 450, and 550°C to doses of 0.01 and 0.1dpa (displacements per atom). DBS was used to develop a better understanding of defect formation in Fe-Cr base materials exposed to low doses. Specifically, the goal of this work is to develop a better fundamental understanding of the evolution of nanoscale and sub-nanoscale defect clusters in neutron irradiated Fe-Cr alloys. The results of this work were fairly complicated due to the fact that α’ precipitation could occur in several of these samples. It was found that in samples where early stages of α’ precipitation is possible, lower S-parameters were determined. The S-parameter is indicative of the number and size of vacancy-type defects in the samples, so a lower S-parameter suggests that chromium segregation reduces the vacancy clustering in these samples. Specific trends for each composition are detailed in the chapters 4 and 5. Overall, chromium content has a major effect on the void nucleation and growth seen in these Fe-Cr model alloys.
Issue Date:2019-12-10
Rights Information:Copyright 2019 Carly Romnes
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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