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Nanocrystalline materials have been proposed as superior radiation tolerant materials in comparison to coarse grain counterparts. However, there is still a limited understanding whether a particular nanocrystalline grain size is required to obtain significant improvements in key deleterious effects resulting from energetic irradiation. This work employs the use of in-situ heavy ion irradiation transmission electron microscopy experiments coupled with quantitative defect characterization and precession electron diffraction to explore the sensitivity of defect size and density within the nanocrystalline regime in platinum. Under the explored experimental conditions, no significant change in either the defect size or density between grain sizes of 20 and 100 nm was observed. Furthermore, the in-situ transmission electron microscopy irradiations illustrate stable sessile defect clusters of 1-3 nm adjacent to most grain boundaries, which are traditionally treated as strong defect sinks. The stability of these sessile defects observed in-situ in small, 20-40 nm, grains is the proposed primary mechanism for a lack of defect density trends. This scaling breakdown in radiation improvement with decreasing grain size has practical importance on nanoscale grain boundary engineering approaches for proposed radiation tolerant alloys.

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TYPE Journal Article YEAR 2018

DOI OSTI Scopus

Characterizing single isolated radiation-damage events from molecular dynamics via virtual diffraction methods

Journal of Applied Physics

Dingreville, Remi P.; Stewart, James A.; Price, Patrick M.; Ji, W.; Franco, M.; Hattar, Khalid M.

The evolution and characterization of single-isolated-ion-strikes are investigated by combining atomistic simulations with selected-area electron diffraction (SAED) patterns generated from these simulations. Five molecular dynamics simulations are performed for a single 20 keV primary knock-on atom in bulk crystalline Si. The resulting cascade damage is characterized in two complementary ways. First, the individual cascade events are conventionally quantified through the evolution of the number of defects and the atomic (volumetric) strain associated with these defect structures. These results show that (i) the radiation damage produced is consistent with the Norgett, Robinson, and Torrens model of damage production and (ii) there is a net positive volumetric strain associated with the cascade structures. Second, virtual SAED patterns are generated for the resulting cascade-damaged structures along several zone axes. The analysis of the corresponding diffraction patterns shows the SAED spots approximately doubling in size, on average, due to broadening induced by the defect structures. Furthermore, the SAED spots are observed to exhibit an average radial outward shift between 0.33% and 0.87% depending on the zone axis. This characterization approach, as utilized here, is a preliminary investigation in developing methodologies and opportunities to link experimental observations with atomistic simulations to elucidate microstructural damage states.

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TYPE Journal Article YEAR 2018

DOI OSTI Scopus

High temperature irradiation induced creep in Ag nanopillars measured via in situ transmission electron microscopy

Scripta Materialia

Jawaharram, Gowtham S.; Price, Patrick M.; Barr, Christopher M.; Hattar, Khalid M.; Averback, Robert S.; Dillon, Shen J.

Irradiation induced creep (IIC) rates are measured in compression on Ag nanopillar (square) beams in the sink-limited regime. The IIC rate increases linearly with stress at lower stresses, i.e. below ≈2/3 the high temperature yield stress and parabolically with pillar width, L, for L less than ≈300 nm. The data are obtained by combining in situ transmission electron imaging with simultaneous ion irradiation, laser heating, and nanopillar compression. Results in the larger width regime are consistent with prior literature.

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TYPE Journal Article YEAR 2018

DOI OSTI DOI Scopus OSTI Scopus