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Real-time thermomechanical property monitoring during ion beam irradiation using in situ transient grating spectroscopy

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Dennett, Cody A.; Buller, Daniel L.; Hattar, Khalid M.; Short, Michael P.

A facility for continuously monitoring the thermal and elastic performance of materials under exposure to ion beam irradiation has been designed and commissioned. By coupling an all-optical, non-contact, non-destructive measurement technique known as transient grating spectroscopy (TGS) to a 6 MV tandem ion accelerator, bulk material properties may be measured at high fidelity as a function of irradiation exposure and temperature. Ion beam energies and optical parameters may be tuned to ensure that only the properties of the ion-implanted surface layer are interrogated. This facility provides complementary capabilities to the set of facilities worldwide which have the ability to study the evolution of microstructure in situ during radiation exposure, but lack the ability to measure bulk-like properties. Here, the measurement physics of TGS, design of the experimental facility, and initial results using both light and heavy ion exposures are described. Finally, several short- and long-term upgrades are discussed which will further increase the capabilities of this diagnostic.

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TYPE Journal Article YEAR 2019
ScopusOSTIDOI

Synthesis of complex rare earth nanostructures using: In situ liquid cell transmission electron microscopy

Nanoscale Advances

Taylor, Caitlin A.; Nenoff, T.M.; Pratt, Sarah H.; Hattar, Khalid M.

Energy and cost efficient synthesis pathways are important for the production, processing, and recycling of rare earth metals necessary for a range of advanced energy and environmental applications. In this work, we present results of successful in situ liquid cell transmission electron microscopy production and imaging of rare earth element nanostructure synthesis, from aqueous salt solutions, via radiolysis due to exposure to a 200 keV electron beam. Nucleation, growth, and crystallization processes for nanostructures formed in yttrium(iii) nitrate hydrate (Y(NO3)3·4H2O), europium(iii) chloride hydrate (EuCl3·6H2O), and lanthanum(iii) chloride hydrate (LaCl3·7H2O) solutions are discussed. In situ electron diffraction analysis in a closed microfluidic configuration indicated that rare earth metal, salt, and metal oxide structures were synthesized. Real-time imaging of nanostructure formation was compared in closed cell and flow cell configurations. Notably, this work also includes the first known collection of automated crystal orientation mapping data through liquid using a microfluidic transmission electron microscope stage, which permits the deconvolution of amorphous and crystalline features (orientation and interfaces) inside the resulting nanostructures.

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TYPE Journal Article YEAR 2019
ScopusOSTIDOI

New nanoscale toughening mechanisms mitigate embrittlement in binary nanocrystalline alloys

Nanoscale

Heckman, Nathan H.; Foiles, Stephen M.; O'Brien, Christopher J.; Chandross, M.; Barr, Christopher M.; Argibay, Nicolas A.; Hattar, Khalid M.; Lu, Ping L.; Adams, David P.; Boyce, Brad B.

Nanocrystalline metals offer significant improvements in structural performance over conventional alloys. However, their performance is limited by grain boundary instability and limited ductility. Solute segregation has been proposed as a stabilization mechanism, however the solute atoms can embrittle grain boundaries and further degrade the toughness. In the present study, we confirm the embrittling effect of solute segregation in Pt-Au alloys. However, more importantly, we show that inhomogeneous chemical segregation to the grain boundary can lead to a new toughening mechanism termed compositional crack arrest. Energy dissipation is facilitated by the formation of nanocrack networks formed when cracks arrested at regions of the grain boundaries that were starved in the embrittling element. This mechanism, in concert with triple junction crack arrest, provides pathways to optimize both thermal stability and energy dissipation. A combination of in situ tensile deformation experiments and molecular dynamics simulations elucidate both the embrittling and toughening processes that can occur as a function of solute content.

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TYPE Journal Article YEAR 2018
ScopusOSTIDOI

Departing from the mutual exclusiveness of strength and ductility in nanocrystalline metals with vacancy induced plasticity

Scripta Materialia

Islam, Zahabul; Wang, Baoming; Hattar, Khalid M.; Gao, Huajian; Haque, Aman

Strength and ductility are mutually exclusive in metallic materials. To break this relationship, we start with nanocrystalline Zirconium with very high strength and low ductility. We then ion irradiate the specimens to introduce vacancies, which promote diffusional plasticity without reducing strength. Mechanical tests inside the Transmission Electron Microscope reveal about 300% increase in plastic strain after self ion-irradiation. Molecular dynamics simulation showed that 4.3% increase in vacancies near the grain boundaries can result in about 60% increase in plastic strain. Both experimental and computational results support our hypothesis that vacancies may enhance plasticity through higher atomic diffusivity at the grain boundaries.

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TYPE Journal Article YEAR 2018
ScopusOSTIDOI
Results 101–125 of 527
Results 101–125 of 527