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Results for “microstructure evolution”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

In situ study on heavy ion irradiation induced microstructure evolution in single crystal Cu with nanovoids at elevated temperature

Understanding the response of nanovoids to irradiation damage advances our capability to design radiation tolerant materials. Recent in situ studies reveal the shrinkage of hexagon-shaped nanovoids in (110) textured Cu. However, the evolution of voids with irregular geometries under irradiation is less well understood. Here, in situ Kr ion irradiation was performed at 100 °C on single-crystal Cu (112) that possesses nanovoids with high aspect ratio. In situ studies show these elongated voids fragment into smaller voids and shrink gradually with increasing dose. Phase field simulations confirm that fragmentation of the void is governed by the competing kinetics between atoms diffusing toward and away from the elongated nanovoid. In conclusion, cost irradiation analysis reveals the formation of high-density defect clusters.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

In-situ TEM study of microstructural evolution in NFA and Cr 3 C 2 @SiC-NFA composite during ion irradiation

In this article, the ion irradiation responses of a Fe-based nanostructured ferritic alloy or ‘NFA’ (Fe–9Cr–2W–0.2V–0.4Ti–0.3Y 2 O 3 ) and a Cr 3 C 2 @SiC-NFA composite were assessed. In-situ ion irradiation with TEM observation was carried out by using 1 MeV Kr ++ ions at doses of 0, 1, 3, 5, 10 dpa and temperatures of 300 °C and 450 °C. Both the NFA and Cr 3 C 2 @SiC-NFA samples showed significant dislocation density after 10 dpa at 300 °C. However, the Cr 3 C 2 @SiC-NFA composite showed a significantly lower dislocation loop density and a smaller average loop size during the irradiation at 450 °C as opposed to the NFA. At 300 °C, 1/2<111> type dislocation loops were observed in both the NFA and Cr 3 C 2 @SiC-NFA samples. Interestingly, at 450 °C, <100> type loops were dominant in the NFA sample while 1/2<111> type loops were still dominant in the Cr 3 C 2 @SiC-NFA sample. The results were discussed based on the large surface sink effects and enhanced interstitial-vacancy recombination at higher temperatures. Lastly, the additional Si element in the Cr 3 C 2 @SiC-NFA sample might have played a significant role in determining the dominant loop types.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Sensitivity of UO 2 fuel performance to microstructural evolutions driven by dilute additives

Use of dilute additives to nuclear fuel is being considered to increase the security of commercial fuel management through traceability of fabricated fuel elements. Taggants, as additives are denoted when included for traceability purposes, may also improve fuel performance, as demonstrated in Cr-containing uranium dioxide as described in the literature, and they may also improve fuel safety. In fact, studies have shown that some additives affect fuel material properties such as grain size and density after sintering. Given the possible range of elements that could be used as additives, the impact of such fuel property variations on the fuel’s thermomechanical behavior becomes relevant. These effects can be evaluated through a sensitivity study of standard fuel models to analyze changes in these properties using a fuel performance code. In this work, the BISON code is being used to investigate these effects through a 2D axisymmetric model of smeared UO 2 fuel pellets and ZIRLO® cladding under realistic pressurized water reactor core irradiation conditions. Here, randomly sampled densities and grain sizes within specified ranges are used as input parameters in the simulations, and several fuel model-related outputs are evaluated. The thermomechanical response of the cladding is also addressed in this study. The simultaneous variation of both input parameters offers a more comprehensive path to identify key sensitivities. Outputs explored include temperature, fission gas release, creep, and radial stress. Results show that although most of these outputs are sensitive to grain size to a certain extent, density mainly affects fuel temperature and elastic strain. Furthermore, sensitivities can vary depending on the radial position within the fuel pellet.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Spatially resolved texture and microstructure evolution of additively manufactured and gas gun deformed 304L stainless steel investigated by neutron diffraction and electron backscatter diffraction

In this study, we report the characterization of a 304L stainless steel cylindrical projectile produced by additive manufacturing. The projectile was compressively deformed using a Taylor Anvil Gas Gun, leading to a huge strain gradient along the axis of the deformed cylinder. Spatially resolved neutron diffraction measurements on the HIgh Pressure Preferred Orientation time-of-flight diffractometer (HIPPO) and Spectrometer for Materials Research at Temperature and Stress diffractometer (SMARTS) beamlines at the Los Alamos Neutron Science CEnter (LANSCE) with Rietveld and single-peak analysis were used to quantitatively evaluate the volume fractions of the α, γ, and ε phases as well as residual strain and texture. The texture of the γ phase is consistent with uniaxial compression, while the α texture can be explained by the Kurdjumov–Sachs relationship from the γ texture after deformation. This indicates that the material first deformed in the γ phase and subsequently transformed at larger strains. The ε phase was only found in volumes close to the undeformed material with a texture connected to the γ texture by the Shoji–Nishiyama orientation relationship. This allows us to conclude that the ε phase occurs as an intermediate phase at lower strain, and is superseded by the α phase when strain increases further. Furthe, we found a proportionality between the root-mean-squared microstrain of the γ phase, dominated by the dislocation density, with the α volume fraction, consistent with strain-induced martensite α formation. In conclusion, knowledge of the sample volume with the ε phase from the neutron diffraction analysis allowed us to identify the ε phase by electron back scatter diffraction analysis, complementing the neutron diffraction analysis with characterization on the grain level.

304L stainless steel↗
DOE OSTI2012

Bulk Nanolayered Composites: Interfacial Influence on Microstructural Evolution at Large Plastic Strains

Conclusions are: (1) As-processed ARB material has similar morphology, chemistry as PVD, but different interfacial structure; (2) Density of interfaces AND interfacial structure play a role in determining hardness, an example is twinning in Cu at the {l_brace}112{r_brace}Cu//{l_brace}112{r_brace}Nb interface and higher strength, no twinning in Cu in the {l_brace}111{r_brace}Cu//{l_brace}110{r_brace}Nb interface; and (3) Need to understand effects of processing history to predict the effects on the interfaces we produce - Amount of strain, Strain Path, Annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructural Evolution Of Iron Oxyfluoride/Carbon Nanocomposites Upon Electrochemical Cycling

High electrochemical performance iron oxyfluoride conversion electrode undergoes complex electrochemical reaction mechanisms upon cycling. In this work, a combination of selected area electron diffraction (SAED) and scanning transmission electron microscopy/electron energy loss spectroscopy (STEM/EELS) analysis techniques have been used to understand the conversion-reconversion mechanisms of FeO 0.7 F 1.3 /C upon cycling. Considerable changes have been observed with cycling. For the fully delithiated electrodes, the nanometer scale intermixing of amorphous rutile and nanocrystalline rocksalt phases is stable up to 20 cycles; however, upon further cycling the amount of amorphous rutile phase decreased and amount of rocksalt phase increased gradually, implying incomplete reconversion reactions with increasing cycle number. In addition, a progressive growth of solid electrolyte interphase (SEI) layer was observed with cycling, which is mainly composed of LiF. Interestingly, Fe 2+ and Fe nanoparticles were found trapped in the SEI layer with increasing cycle number. Upon cycling, the combined progressive increase in Fe 2+ content and insulating LiF (from SEI and conversion product) give rise to the observed capacity loss.

25 ENERGY STORAGE↗