Date of Award

1-1-2012

Document Type

Campus Access Thesis

Department

Mechanical Engineering

First Advisor

Djamel Kaoumi

Abstract

Ferritic/martensitic steels are candidate materials for structural and cladding components designed for Generation IV reactors because of their superior resistance to radiation damage at the high operating temperatures envisioned in these reactors. To enable the development and optimization of such advanced alloys for in-reactor use, a fundamental understanding of radiation damage accumulation in materials is required. Especially, in order to predict the in-reactor performance of ferritic/martensitic alloys, it is essential to understand the basic mechanisms of radiation damage formation (loop density, defect interactions), accumulation (loop evolution, precipitation or dissolution of second phases...), and its effects on the material properties.

In this work, two model alloys (one ferritic/martensitic steel of composition Fe-12Cr-0.1C and one fully martensitic steel of composition Fe-9Cr-0.1C) were custom-made with the intent of reproducing the type of starting microstructure of F/M steels, but without the complications of additional alloying elements. The model alloys were irradiated with 1 MeV Kr ions at 50K, 180K, 298K, 473K and 673K to doses up to 10 dpa in-situ in a TEM. The microstructure evolution under irradiation was followed and characterized at successive doses in terms of irradiation-induced defect formation and evolution, black dot density, and stability of as-fabricated microstructure (i.e. dislocation networks, lath boundaries, carbides) using weak-beam dark-field imaging and g.b analysis. The effect of the irradiation temperature on the damage density and on the stability of the initial microstructure is assessed for these doses. The overall goal of the irradiations is to perform a direct determination of the spatial correlation of the time evolution of the irradiation-induced defect structures with the pre-existing alloy microstructure, for comparison with computational simulations developed (at University of Tennessee) using a spatially dependent rate theory model of cluster evolution in both compositional and geometric spaces under conditions of high energy ion irradiation. This computational simulation will help predict radiation damage in materials for future Generation IV reactors, which lacks of experimental data.

Rights

© 2012, Jimmy Lewis Adamson IV

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