The Role of Electrons During In-Situ Heavy Ion Irradiation of Fe & Fe-Cr Alloys
Zhongwen Yao

Using a combination of Fe+ and Xe+ ion irradiations of Fe and Fe-Cr alloys, the author studied the dislocation loops in the metals in IVEM at Argonne National Lab. Observation with the electron microscope meant that there was subsequent irradiation with electrons. In regions of electron irradiation, a decrease in loop density was measured, and there appeared to be a loss of dislocation loops with increasing electron irradiation dose. The study shows that electron irradiation was partially responsible for loss of loops, likely to the surface of the sample. Additionally, the results suggest that surface contamination of carbon may be responsible for preventing nucleation of loops during ion irradiation.


Molecular Dynamics Study of Interstitial C Atoms in bcc Iron: Migration and Interaction with Radiation-Produced Point Defects and Defect Clusters
Kanit Tapasa

Using MD studies the author found that vacancies complexes with C are immobile. Previous modeling work is in contradiction with experimental results. Therefore, new empirical inter-atomic potentials were developed to properly model this work.


Interactions Between Interstitial Loops in α-Fe and Fe-Cr Alloys
Dmitry Terentyev

The purpose of this work is to study small <111> dislocation loops by varying the Cr content of the alloy and then comparing the loop-loop interactions. Results show that loops are able to form new types of sessile configurations due to the decrease in total length of the dislocation line. Junctions between merged SIA clusters are di-interstitials. Increasing the Cr content decreases the binding energy of sessile configuration and thus reducing their stability.


Microstructural Characterization of Ion-Irradiated Ultra High Purity Fe by Experimental and Modeling Methods
Mercedes Hernández-Mayoral

TEM characterization of the UHP iron shows that the surface effects dominate loop stability. In order to accurately characterize loop density, both thin and thich regions should be analyzed to eliminate surface effects. Computational simulation using KMC over-estimates defect concentration by failing to account for loop coarsening.


Defect Interactions with He Bubbles
Brian Wirth

With a combination of MD simulations using embedded atom method (EAM) potentials and dynamic TEM experiments, the interactions of dislocations with He bubbles can be studied. The strength of He bubbles as obstacles to dislocation movement depends strongly on the internal pressure of the bubbles, but also on the geometry of interaction with the bubble by the dislocation. Future work will compare other materials to try to determine the physics of the interactions on a fundamental level.


Modeling Point Defect Interactions in Fe-Cr Alloys
Brian Wirth

In order to understand point defect interactions in Fe-Cr alloys, it is necessary to understand the thermodynamic, electronic and magnetic effects in the alloy, and how those effects differ between Fe and Cr. The approach is to use ab initio (VASP), including collinear magnetic spins, and then translate materials parameters to MD simulations to look at size effects, point defect – Cr interactions and cascade defect production. The work demonstrates that there are strong electronic/magnetic interactions that occur between the Cr and Fe. Cr diffusion is faster than Fe diffusion because Cr diffusion through a vacancy mechanism.