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Topic Title: Microstructural Processes in Irradiated Materials: Defect ClustPosterers and fundamental radiation effects
Topic Summary: Thursday AM session
Created On: 3/1/2007 12:55 PM

 3/1/2007 12:55 PM

Gaurav Gupta

Posts: 4
Joined: 2/27/2007

1) Dynamics of Nanometer-Sized Interstitial-Type Dislocation Loops in Iron by In-situ TEM

Kazuto Arakawa

Role of self-interstitial atom clusters in microstructural evolution induced by irradiation was studied. Molecular dynamics has been used to simplify and explain the dynamic behavior of small interstitial type dynamic loops. Knowledge of these loops by experiment is still not very clear. BCC iron was subjected to electron irradiation and these loops were studied in in-situ TEM.

2) TEM characterization of Defects in Fe: A Simulation Point of View

Robin Schaeublin

The aim is to understand the limits of TEM by simulation to study the nanometric defects in iron and ferritic steels produced by irradiation. Molecular dynamic simulations were used with empirical potentials. TEM simulations were based on multislice methods. Limitations which impede the characterization of nanometric defects were discussed.

3) Vacancy and Vacancy Cluster Properties in BCC Transition Metals Investigated by Density Functional Theory

Charlotte Becquart

Formation and binding energy of vacancy and vacancy clusters were determined by ab- initio calculations. BCC transition metals were compared. Each class of metals behaved differently according to their position in the periodic table. All the values were evaluated and compared.

4) Self-Interstitial Defects in Hcp Metals from First Principles: New Structures and Migration Paths

Guillaume Verite

Properties of interstitial defects in Zr (HCP) structure were studied. They are important to understand microstructural evolution in irradiation. A systematic study was performed using the SIESTA code of the study of interstitials in Zr, Hf. Two new families of low energy and low symmetry were found. Discrepancies with empirical potential results were discussed. Migration paths were computed in Zr.

5) The Effect of Interface Structure of the Reduction of Radiation Damage in CuNb Multilayers

Michael Demkowiczu

Simulations of radiation damage cascades show that CuNb interfaces remain stable under 33KeV irradiation. The number of interstitials created is half that in regular FCC and BCC Nb. Origin of reduction in radiation damage were described. Behavior of point defects was found to be dependent on the atomic arrangement at the interfaces. Based on these results other pairs which depict reduced radiation damage were identified.

6) Grain Growth in Nanocrystalline Metal Thin Films under In Situ Ion Beam Irradiation Viewed as a Thermal Spike Phenomenon: Experiment vs. Theory

Djamel Kaoumi

Grain growth in nanocrystalline thin films was studied under ion-beam irradiation. This was done in-situ TEM at varying temperatures. Average grain size increased with ion dose. Temperature-wise three regimes were observed: 1) low temperature, 2) high temperature and, 3) a thermal regime. A formula for grain boundary mobility was derived which is independent of temperature in ballistic range.

7) Molecular Dynamics Simulation of Radiation Damage in Uranium Dioxide

Taku Watanabe
Radiation causes point defects to migrate, annihilate and degrade within the crystal. Over short time collision cascades create damage which anneal quickly. Molecular dynamic study was done to find the damage in the microstructure of uranium dioxide. Two different models for atomic interactions were compared. The major differences are the charges of uranium and oxygen atoms. Simulations were done by giving large energy to primary knock on atoms.

8) A Modified Hard-Sphere Model for the Viscosity of Irradiated U-Si and U-Al Alloys

Jeffrey Rest

Irradiated U-Si compounds were found to go amorphous under irradiation and undergo gas-bubble swelling. A hard sphere model of binary fluids is designed and applied to U-Si and U-Al systems, which views each alloy before mixing as hard spheres of suitable diameter and then later the diameter is adjusted after mixing. The principle difference between liquid and real particles is the attractive force leading to cohesion of the liquid.

9) Influence of Delta-Phase Metastability of the Radiation Damage Properties of Plutonium-Gallium Alloys

Steven Volane

Modeling the evolution of Pu-Ga alloys is important to understand how these materials age. Aging emanates from spontaneous fission of Pu resulting in daughter products like He and uranium. Modified embedded atom method was used and applied to Pu-Ga-He system. Behavior of defects in the fcc phase of Pu based materials is influenced by metastability of this phase.

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