G. Vetterick

Texture evolution in nanocrystalline iron films deposited using biased magnetron sputtering

Fe thin films were deposited on sodium chloride (NaCl) substrates using magnetron sputtering to investigate means of texture control in free standing metal films. The Fe thin films were studied using transmission electron microscopy equipped with automated crystallographic orientation microscopy. Using this technique, the microstructure of each film was characterized in order to elucidate the effects of altering deposition parameters. The natural tendency for Fe films grown on (100) NaCl is to form a randomly oriented nanocrystalline microstructure. By careful selection of substrate and deposition conditions, it is possible to drive the texture of the film toward a single (100) orientation while retaining the nanocrystalline microstructure.

Achieving Radiation Tolerance through Non-Equilibrium Grain Boundary Structures

Many methods used to produce nanocrystalline (NC) materials leave behind non-equilibrium grain boundaries (GBs) containing excess free volume and higher energy than their equilibrium counterparts with identical 5 degrees of freedom. Since non-equilibrium GBs have increased amounts of both strain and free volume, these boundaries may act as more efficient sinks for the excess interstitials and vacancies produced in a material under irradiation as compared to equilibrium GBs. The relative sink strengths of equilibrium and non-equilibrium GBs were explored by comparing the behavior of annealed (equilibrium) and as-deposited (non-equilibrium) NC iron films on irradiation. These results were coupled with atomistic simulations to better reveal the underlying processes occurring on timescales too short to capture using in situ TEM. After irradiation, NC iron with non-equilibrium GBs contains both a smaller number density of defect clusters and a smaller average defect cluster size. Simulations showed that excess free volume contribute to a decreased survival rate of point defects in cascades occurring adjacent to the GB and that these boundaries undergo less dramatic changes in structure upon irradiation. These results suggest that non-equilibrium GBs act as more efficient sinks for defects and could be utilized to create more radiation tolerant materials in future.

Coupling Quantitative Dislocation Analysis with In Situ Loading Techniques: New Insight into Deformation Mechanisms

The vast majority of our understanding about the deformation mechanisms in nanocrystalline materials is limited to information gained from experimental and theoretical characterization of FCC materials. Related behavior in nanocrystalline BCC materials is not as frequently studied, and thus outstanding questions remain regarding deformation regimes and Hall-Petch trends. Through the use of coupled insitu TEM tensile testing and quantitative dislocation density analysis via precession electron diffraction, a study of deformation in nanocrystalline iron films was performed.

Correlation of Microstructure and Mechanical Properties in Nuclear Reactor Stainless Steels

Stainless steels used in nuclear reactors experience extreme conditions during operation, requiring microstructures capable of withstanding temperature, stress, and irradiation without experiencing negative effects. One detrimental result of these extreme conditions is radiation induced segregation (RIS), which causes a redistribution of the atomic structure of the material, most notably at grain boundaries. This can lead to a change in the mechanical properties of the materials, such as grain boundary embrittlement [1].