In situ transmission electron microscopy (TEM) observation of UO2 single crystal irradiated with Kr ions at high temperatures was conducted to understand the dislocation evolution due to high-energy ...radiation. The dislocation evolution in UO2 single crystal is shown to occur as nucleation and growth of dislocation loops at low-irradiation doses, followed by transformation to extended dislocation segments and networks at high doses, as well as shrinkage and annihilation of some loops and dislocations due to high temperature annealing. Generally the trends of dislocation evolution in UO2 were similar under Kr irradiation at different ion energies and temperatures (150keV at 600°C and 1MeV at 800°C) used in this work. Interstitial-type dislocation loops with Burgers vector along 〈110〉 were observed in the Kr-irradiated UO2. The irradiated specimens were denuded of dislocation loops near the surface.
Swift heavy ion induced radiation damage is investigated for ceria (CeO2), which serves as a UO2 fuel surrogate. Microstructural changes resulting from an irradiation with 940 MeV gold ions of 42 ...keV/nm electronic energy loss are investigated by means of electron microscopy accompanied by electron energy loss spectroscopy showing that there exists a small density reduction in the ion track core. While chemical changes in the ion track are not precluded, evidence of them was not observed. Classical molecular dynamics simulations of thermal spikes in CeO2 with an energy deposition of 12 and 36 keV/nm show damage consisting of isolated point defects at 12 keV/nm, and defect clusters at 36 keV/nm, with no amorphization at either energy. Inferences are drawn from modeling about density changes in the ion track and the formation of interstitial loops that shed light on features observed by electron microscopy of swift heavy ion irradiated ceria.
Oxide materials are used in numerous applications such as thermal barrier coatings, nuclear fuels, and electrical conductors and sensors, all applications where nanometer-scale stoichiometric changes ...can affect functional properties. Atom probe tomography can be used to characterize the precise chemical distribution of individual species and spatially quantify the oxygen to metal ratio at the nanometer scale. However, atom probe analysis of oxides can be accompanied by measurement artifacts caused by laser-material interactions. In this investigation, two technologically relevant oxide materials with the same crystal structure and an anion to cation ratio of 2.00, pure cerium oxide (CeO2) and uranium oxide (UO2) are studied. It was determined that electronic structure, optical properties, heat transfer properties, and oxide stability strongly affect their evaporation behavior, thus altering their measured stoichiometry, with thermal conductance and thermodynamic stability being strong factors.
While identifying guiding principles in addressing diversity challenges is important, DMMM1 organizers also made it their mission to distill what was learned into a practical "toolkit" of concrete ...action steps, novel and tested strategies, and effective recommendations. This toolkit-as well as the full report of what was shared at the summit and downloads of key presentations-is available to all in the "Resources" section of the summit website at www.tms.org /diversitysummit.
Swift heavy ion induced radiation damage is investigated for ceria (CeO2), which serves as a UO2 fuel surrogate. Microstructural changes resulting from an irradiation with 940 MeV gold ions of 42 ...keV/nm electronic energy loss are investigated by means of electron microscopy accompanied by electron energy loss spectroscopy showing that there exists a small density reduction in the ion track core. While chemical changes in the ion track are not precluded, evidence of them was not observed. Classical molecular dynamics simulations of thermal spikes in CeO2 with an energy deposition of 12 and 36 keV/nm show damage consisting of isolated point defects at 12 keV/nm, and defect clusters at 36 keV/nm, with no amorphization at either energy. Furthermore, inferences are drawn from modeling about density changes in the ion track and the formation of interstitial loops that shed light on features observed by electron microscopy of swift heavy ion irradiated ceria.
The work-hardening behavior of hexagonal-close-packed (hcp) metals, such as hafnium, is influenced by temperature, strain rate, chemistry, and texture. In the case of hafnium, while slip on the prism ...and pyramidal planes is dominant during deformation, the propensity of deformation twinning is known to increase with decreasing temperature and increasing strain rate. In this study, hafnium was prestrained quasi-statically in compression at liquid nitrogen temperature (77 K), creating a heavily twinned microstructure. The specimens were then reloaded in compression at room temperature (298 K). Yield stress, flow stress, and work-hardening behaviors of the prestrained specimens were higher than room-temperature compression test data typical of the as-annealed material. The microstructure of each specimen was characterized optically and using a transmission electron microscope (TEM). Texture was measured by neutron diffraction and the texture evolution due to twinning, and the interaction of slip with the twins was seen to lead to higher work-hardening rates and flow stresses in the cold prestrained specimens. PUBLICATION ABSTRACT
In situ transmission electron microscopy (TEM) observation of UO sub(2) single crystal irradiated with Kr ions at high temperatures was conducted to understand the dislocation evolution due to ...high-energy radia-tion. The dislocation evolution in UO sub(2) single crystal is shown to occur as nucleation and growth of dislo-cation loops at low-irradiation doses, followed by transformation to extended dislocation segments and networks at high doses, as well as shrinkage and annihilation of some loops and dislocations due to high temperature annealing. Generally the trends of dislocation evolution in UO sub(2) were similar under Kr irra-diation at different ion energies and temperatures (150 keV at 600 degreesC and 1 MeV at 800 degreesC) used in this work. Interstitial-type dislocation loops with Burgers vector along were observed in the Kr-irradi-ated UO sub(2). The irradiated specimens were denuded of dislocation loops near the surface.
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