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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Uncovering metallic glasses hidden vacancy-like motifs using machine learning

Vacancies are a ubiquitous type of defect in crystalline materials that can affect their properties and behavior, including atomic diffusivity, deformation processes, thermal conductivity, and electrical conductivity. While well-defined in crystals, it is challenging to identify such topological footprints in the amorphous structure of metallic glasses (MGs). Here, we uncover an unforeseen vacancy-like structural motif named Q7, which refers to an atomic Voronoi polyhedron with seven quadrangular faces, by investigating MG local atomic configurations with the help of machine learning. The Q7 motif exhibits characteristics similar to crystalline vacancies and plays a significant role in short-range structural disorder in MGs. The atoms at the center of the Q7 motif display larger local entropy, atomic volume, and local tension. Additionally, its concentration follows an Arrhenius-like relationship with temperature, accurately indicating the glass transition temperature, and is strongly correlated with the yield and failure of MGs during mechanical deformation. The discovery of the Q7 motif provides new insights into understanding the intricate relationship between local disorder and structural relaxation in MGs, offering a remarkable ability to predict their thermal and mechanical behavior. This potentially paves the way for enhancements in the design and manufacturing processes of MGs and other amorphous materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Micropillar Compression of Additively Manufactured 316L Stainless Steels after 2 MeV Proton Irradiation: A Comparison Study between Planar and Cross-Sectional Micropillars

A micropillar compression study with two different techniques was performed on proton-irradiated additively manufactured (AM) 316L stainless steels. The sample was irradiated at 360 °C using 2 MeV protons to 1.8 average displacement per atom (dpa) in the near-surface region. A comparison study with mechanical test and microstructure characterization was made between planar and cross-sectional pillars prepared from the irradiated surface. While a 2 MeV proton irradiation creates a relatively flat damage zone up to 12 µm, the dpa gradient by a factor of 2 leads to significant dpa uncertainty along the pillar height direction for the conventional planar technique. Cross-sectional pillars can significantly reduce such dpa uncertainty. From one single sample, three cross-sectional pillars were able to show dpa-dependent hardening. Furthermore, post-compression transmission electron microscopy allows the determination of the deformation mechanism of individual micropillars. Cross-sectional micropillar compression can be used to study radiation-induced mechanical property changes with better resolution and less data fluctuation.

transmission electron microscopy↗
DOE OSTI2023

Nanoscale phase transition in impact indented Mo/Cu thin films

The study reveals a size effect in deformation mechanisms via unique structural transitions in sputter deposited fcc/bcc nanolayers under high strain rate impact nanoindentation as layer thickness is reduced from around 100-200 nm to around 5 nm. Here, the indented 5 nm Cu/5 nm Mo multilayer films characterized via cross-sectional scanning/transmission electron microscopy have revealed a phase transition in the 5 nm thick Mo layers from BCC to a coherent metastable FCC structure and fine deformation twins in the 5 nm Cu layers inside a shear band that is approximately 500 nm long and inclined to the layer interfaces. In contrast, thicker layers, 80 nm Cu/180 nm Mo, show different deformation behavior with uneven layer thickness reduction, shearing of Cu layers, and bending of the columnar Mo grains beneath the indentation without any sign of shear band and localized phase transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-resolution source imaging and moment tensor estimation of acoustic emissions during brittle creep of basalt undergoing carbonation

SUMMARY As the high-frequency analogue to field-scale earthquakes, acoustic emissions (AEs) provide a valuable complement to study rock deformation mechanisms. During the load-stepping creep experiments with CO2-saturated water injection into a basaltic sample from Carbfix site in Iceland, 8791 AE events are detected by at least one of the seven piezoelectric sensors. Here, we apply a cross-correlation-based source imaging method, called geometric-mean reverse-time migration (GmRTM) to locate those AE events. Besides the attractive picking-free feature shared with other waveform-based methods (e.g. time-reversal imaging), GmRTM is advantageous in generating high-resolution source images with reduced imaging artefacts, especially for experiments with relatively sparse receivers. In general, the imaged AE locations are found to be scattered across the sample, suggesting a complicated fracture network rather than a well-defined major shear fracture plane, in agreement with X-ray computed tomography imaging results after retrieval of samples from the deformation apparatus. Clustering the events in space and time using the nearest-neighbour approach revealed a group of ‘repeaters’, which are spatially co-located over an elongated period of time and likely indicate crack, or shear band growth. Furthermore, we select 2196 AE events with high signal-to-noise-ratio (SNR) and conduct moment tensor estimation using the adjoint (backpropagated) strain tensor fields at the locations of AE sources. The resulting AE locations and focal mechanisms support our previously assertion that creep of basalt at the experimental conditions is accommodated dominantly by distributed microcracking.

58 GEOSCIENCES↗
DOE OSTI2020

Measurements of a quantum bulk acoustic resonator using a superconducting qubit

Phonon modes at microwave frequencies can be cooled to their quantum ground state using conventional cryogenic refrigeration, providing a convenient way to study and manipulate quantum states at the single phonon level. Phonons are of particular interest because mechanical deformations can mediate interactions with a wide range of different quantum systems, including solid-state defects, superconducting qubits, and optical photons when using optomechanically active constructs. Phonons, thus, hold promise for quantum-focused applications as diverse as sensing, information processing, and communication. Here, we describe a piezoelectric quantum bulk acoustic resonator (QBAR) with a 4.88 GHz resonant frequency, which, at cryogenic temperatures, displays large electromechanical coupling strength combined with a high intrinsic mechanical quality factor, Q i ≈ 4.3 × 10 4 . Using a recently developed flip-chip technique, we couple this QBAR resonator to a superconducting qubit on a separate die and demonstrate the quantum control of the mechanics in the coupled system. Furthermore, this approach promises a facile and flexible experimental approach to quantum acoustics and hybrid quantum systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

A strain density function to analyze particle size effects during high velocity impacts of yttria

Here, the impact behavior of a single yttria (Y 2 O 3 ) nanoparticle onto a Y 2 O 3 substrate is studied as a function of particle velocity (300–1200 m/s) and diameter (12–50 nm) using molecular dynamics simulations. To analyze the results, a strain density function is developed to provide both quantitative and qualitative information about the deformation mechanisms that contribute to the final state of the system. This function provides both clear evidence of shear localization and insight into the conditions for which localization occurs during the impact of Y 2 O 3 particles as they approach experimentally relevant sizes. Further analysis shows that localization and fragmentation only occur for Y 2 O 3 impacts with diameters of at least 50 nm, while particles with diameters of 25 nm and smaller deform primarily by amorphization and viscous flow. Implications for the deposition of films of Y 2 O 3 and other rare-earth oxides via the micro cold spray process are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Strain dependence of Auger recombination in 3 μm GaInAsSb/GaSb type-I active regions

We differentiate the effect of strain induced by lattice-mismatched growth from strain induced by mechanical deformation on cubic nonradiative Auger recombination in narrow-gap GaInAsSb/GaSb quantum well (QW) heterostructures. The typical reduction in the Auger coefficient observed with lattice-mismatched growth appears to be due to the concomitant compositional change rather than the addition of strain, with implications for mid-IR semiconductor laser design. We induced a range of internal compressive strain in five samples from -0.90% to -2.07% by varying the composition during the growth and mechanically induced a similar range of internal strain in analogous quantum well membrane samples. We performed time-resolved photoluminescence and differential reflectivity measurements to extract the carrier recombination dynamics, taken at 300 K with carrier densities from 2.7 × 10 18 cm -3 to 1.4 × 10 19 cm -3 . We observed no change with strain in the cubic Auger coefficient of samples that were strained mechanically, but we did observe a trend with strain in samples that were strained by the QW alloy composition. Measured Auger coefficients ranged from 3.0 × 1 0 - 29 cm 6 s -1 to 3.0 × 1 0 - 28 cm 6 s -1 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Serrated flow in $\mathrm{NaI:Tl}$ scintillator crystals

We report the serrated-flow behavior is an important phenomenon that unveils material-deformation mechanisms, as reported for various kinds of materials. NaI doped with Tl (NaI:Tl) is unique among scintillation materials in that the structure contains glide planes that are linked to serration behavior. In the present work, single crystals of NaI:Tl were subjected to room-temperature compression experiments at different strain rates. The serrated flow was observed, and complexity and multifractal analyses were performed to analyze the serration behavior. The findings revealed that the strain rate had a pronounced effect on the complexity and multifractality of the serrated flow, similar to what has been found in other alloy systems. The results also indicate that there may be a strong link between the complexity of the serrated flow behavior and the heterogeneity of the underlying dynamics. It is expected that the present work could be a step toward a better understanding of the deformation behavior and forgeability of NaI:Tl single crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure

As circuitry approaches single nanometer length scales, it has become important to predict the stability of single nanometer-sized metals. The behavior of metals at larger scales can be predicted based on the behavior of dislocations, but it is unclear if dislocations can form and be sustained at single nanometer dimensions. Here, we report the formation of dislocations within individual 3.9 nm Au nanocrystals under nonhydrostatic pressure in a diamond anvil cell. We used a combination of x-ray diffraction, optical absorbance spectroscopy, and molecular dynamics simulation to characterize the defects that are formed, which were found to be surface-nucleated partial dislocations. These results indicate that dislocations are still active at single nanometer length scales and can lead to permanent plasticity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Auxetic Two-Dimensional Nanostructures from DNA

Architectured materials exhibit negative Poisson's ratios and enhanced mechanical properties compared with regular materials. Their auxetic behaviors emerge from periodic cellular structures regardless of the materials used. The majority of such metamaterials are constructed by top-down approaches and macroscopic with unit cells of microns or larger. There are also molecular auxetics including natural crystals which are not designable. There is a gap from few nanometers to microns, which may be filled by biomolecular self-assembly. In this work, we demonstrate two-dimensional auxetic nanostructures using DNA origami. Structural reconfigurations are performed by two-step DNA reactions and complemented by mechanical deformation studies using molecular dynamics simulations. We find that the auxetic behaviors are mostly defined by geometrical designs, yet the properties of the materials also play an important role. From elasticity theory, we introduce design principles for auxetic DNA metamaterials.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Nanoparticle Surface Passivation Strategies to Improve the Cycle and Calendar Lifetime of Silicon Anodes in Standard Carbonate Electrolytes

Silicon Lithium alloys (SiLix) as the anode active material in a Li-Ion battery configuration offer possible energy densities paralleled only by pure lithium metal. However, the extreme mechanical deformation of alloying and dealloying SiLix through charge/discharge cycles paired with the highly reactive interface of SiLix which generates an interfacial layer known as the solid-electrolyte-interphase are large barriers to industrial adoption of high-silicon-content negative electrodes. Moreover, these challenges are magnified when the thickness of the electrode is brought to relevant levels (>3 mg/cm2). Here, I describe our efforts to address these challenges by utilizing single-nanometer-scale silicon nanoparticles to reduce capacity fade related to mechanical failure. I also detail our efforts to modify the silicon surface through interfacial chemical engineering strategies to passivate the silicon surface. This development three different majority silicon electrodes (50-74 wt%) to achieve cycle capacity retention of greater than 73% through 1000 charge/discharge cycles against capacity-matched NMC-based cathodes and calendar lifetimes greater than one year. This research is a part of the multi-national lab Silicon Consortium Project.

anodes↗
DOE OSTI2023

Development of an in situ ion irradiation scanning electron microscope

An in situ ion irradiation scanning electron microscope (I 3 SEM) has been developed, installed, and integrated into the Ion Beam Laboratory at Sandia National Laboratories. The I 3 SEM facility combines a field emission, variable pressure, scanning electron microscope, a 6 MV tandem accelerator, high flux low energy ion source, an 808 nm-wavelength laser, and multiple stages to control the thermal and mechanical state of the sample observed. The facility advances real-time understanding of materials evolution under combined environments at the mesoscale. As highlighted in multiple examples, this unique combination of tools is optimized for studying mesoscale material response in overlapping extreme environments, allowing for simultaneous ion irradiation, implantation, laser bombardment, conductive heating, cooling, and mechanical deformation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Strain-dependent luminescence and piezoelectricity in monolayer transition metal dichalcogenides

The modification of optical and electronic properties of transition metal dichalcogenides via mechanical deformation has been widely studied. Their ability to withstand large deformations before rupture has enabled large tunability of the bandgap, and further, the spatially varying strain has been shown to control the spatial distribution of the bandgap and lead to effects such as carrier funneling. Monolayer transition metal dichalcogenides exhibit a significant piezoelectric effect that could couple to a spatially inhomogeneous strain distribution to influence electronic and optical behavior. We investigate both experimentally and theoretically an example case of photoluminescence in structures with a strain distribution similar to that employed in single-photon emitters but generated here via nanoindentation. Using a mechanical model for strain induced by nanoindentation, we show that piezoelectricity can result in charge densities reaching 10 12 e/cm 2 and can generate electrostatic potential variations on the order of ±0.1 V across the suspended monolayer. We analyze the implications of these results for luminescence and exciton transport in monolayer transition metal dichalcogenides with spatially varying strain.

42 ENGINEERING↗
DOE OSTI2020

Plastic deformation of single crystals of the equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy in tension and compression from 10 K to 1273 K

In this report the plastic deformation behavior of single crystals of the quinary, equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy (HEA) with the face-centered cubic structure has been investigated in tension and compression as a function of crystal orientation and temperature from 10 K to 1373 K. The critical resolved shear stress (CRSS) for {111}<110> slip at room temperature is 42-45 MPa. It does not depend much on crystal orientation (i.e., the Schmid law holds true) and the sense (tension vs. compression) of the applied load. The CRSS for {111}<110> slip increases with the decrease in temperature, without showing any significant inertia effects at cryogenic temperatures below 77 K. Extrapolation from the measured yield stresses down to 10 K yields a CRSS value at 0 K of 168 MPa. At cryogenic temperatures, the measured strain-rate sensitivity of flow stress is consistent with a very small activation volume. The concept of stress equivalence holds true both for the temperature dependence of CRSS and the stress dependence of activation volume, indicating that solid-solution hardening is the major strengthening mechanism. Deformation twinning occurs at 77 K but not at room temperature, resulting in higher tensile elongation to failure at 77 K than at room temperature. Deformation twinning at 77 K occurs at a shear stress of 378 MPa on conjugate ($\bar1\bar11$) planes in the form of Lüders deformation after large plastic strain (about 85%) achieved by the stage I (easy glide) and stage II (linear work-hardening) deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Small Scale Creep Testing of 14YWT via In-situ Transmission Electron Microscopy Irradiation and Nanoindentation

The next generation of nuclear materials must withstand harsh operating conditions such as high temperatures and irradiation doses. Nanostructured ferritic alloys like oxide dispersion strengthened steels, especially 14YWT, have shown promise as a structural material to withstand these harsh operating conditions. For application, understanding the irradiation enhanced creep of the structural components is fundamental to evaluating the service life in a reactor. Challenges with evaluating irradiation enhanced creep are related to the limited space in nuclear reactors and the expense of conducting post irradiation experiments on irradiated cladding. Ion irradiations are considered to expedite irradiation testing, but such experiments have restricted depth of penetration into the material, limiting the ability to characterize changes to material properties after irradiation. Small scale mechanical testing can be used with ion beam irradiations as a potential avenue to evaluate the irradiation enhanced creep of materials. In this study, in-situ transmission electron microscopy nanopillar creep studies on 14YWT were performed and simultaneously ion beam irradiated with 2.8 MeV Au4+ ions. It was observed that the ion beam irradiation did increase the measured strain rate of the materials. In addition, ex-situ nanoindentation creep studies were performed over a range of temperatures on control 14YWT, and it was observed that there was a change in the deformation mechanism between 873 K and 1073 K that agrees well with macro-scale mechanical testing. Furthermore, these results show promise for applying these techniques to nuclear materials in the future.

14 YWT↗
DOE OSTI2024

In-situ determination of strain during transient burst testing and the temperature dependence of Zircaloy-4 claddings

Understanding fuel system behavior during postulated loss-of-coolant accidents is pertinent for continued safe and efficient operation of light water reactors, particularly as higher burnups are being pursued and safety margins re-evaluated. Conventional mechanical models for the incumbent Zr alloys typically rely on the assumption that steady-state creep is the dominant fuel cladding response during transient accident conditions. To investigate this assumption, simulated accident burst testing was performed on Zircaloy-4 claddings with balloon behavior measured in-situ. Here, two distinct loading conditions were utilized during burst testing: (1) constant-gas-inventory where pressure was allowed to increase with temperature and (2) constant pressure. In-situ strains and strain rates were measured via 2-dimensional digital image correlation techniques and synchronized with temperature to determine deformation dependencies. The temperature dependence of strain rate was characterized by a two segment Arrhenius relationship, with a distinct transition between the high and low temperature/strain regimes. The average activation energy of the lower temperature/strain regime was 328 ± 25 kJ/mol, in agreement with the ~320 kJ/mol used for conventional LOCA models. However, the higher temperature/strain segment, which encompassed most of ballooning, showed increased activation energies as well as a dependence on whether the burst region was in view. For tests that burst away from the camera view, the average high temperature/strain segment activation energy was 635 ± 150 kJ/mol. For samples where the rupture opening formed in view, the average activation energy was 1015 ± 179 kJ/mol. This observed shift in temperature dependence indicates a transition in deformation mechanism at the end of life, possibly to time independent failure mechanisms, which has not yet been visualized in the literature for Zr alloys. Parameters at the transition points were analyzed to determine thresholds for this change in behavior, which occurred at an average hoop strain of 6.9 ± 2.1 %.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Correlations of multiscale structural evolution and homogeneous flows in metallic glass ribbons

Studying the flow behavior is critical to understand the deformation mechanism of amorphous solids. However, detecting the basic flow events in amorphous solids is challenging. Here, by simultaneous SAXS/WAXS, elementary flow carriers in wound metallic glasses are identified from flow-induced structural heterogeneities with a radius of gyration of 2.5~3.5 nm. Their size increases and morphology changes from sphere-like to rod-like under flow. Moreover, the atomic structure exhibits an unusual change to a more disordered state during winding/annealing at the temperature of ~0.8 T g . This work provides an atomic-to-nanoscale description of the flow carriers of amorphous solids during deformation. Impact Statement The elementary flow carriers in metallic glasses have a radius of gyration of 2.5~3.5 nm. During flow, their size increases and morphology changes from sphere-like to rod-like.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Multiscale Mechanisms of Twisted Carbon Nanotube Yarns Probed In Situ by Soft X-rays during Tensile Loading

Piecing together carbon nanotubes (CNTs) into assemblies has so far failed to achieve the same elite strength performance metrics as individual CNTs, highlighting a critical deficiency in understanding the effects that the processing of individual nanostructures have on the performance of their derived macroscale assemblies, thereby hindering the development of a process-structure-performance map for these materials. Here, in this work, we propose a method to decouple the distribution orientation of nanoscale tortuosity and the microscale twist of CNT dry-spun yarns under applied loads via in situ soft X-ray probing at high energy (1200 eV) and low energy (280 eV), respectively. With this decoupling enabled by in situ soft X-ray scattering, we acquired a deeper understanding of the deformation mechanisms of these yarns. We found that for untreated yarns, the twist angle of collective CNT bundles at the macroscale is more sensitive to applied stress than the nanoscale alignment distribution. We also found that increasing nominal twist densities of yarns as well as increased strengthening via plasma treatments and polymer infiltration act to decrease the yarns’ sensitivity to realignment at the nanoscale and prevent failure by the slip mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗