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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Scanning Transmission Electron Microscopy–Atom Probe Tomography Correlative Analysis for the Characterization of Solute-defect Interactions

Atom probe tomography (APT) and (scanning) transmission electron microscopy ((S)TEM) are complementary techniques that provide spatially resolved chemical and structural information at the atomic scale. Here, in this study, we employ two different STEM/APT correlative analysis methods to investigate Cr segregation at dislocation loops in ultra-high purity Fe–Cr alloys. APT needles for the correlative analysis were extracted either from bulk material or from thinned TEM lamellae. STEM analysis was used to determine the Burgers vectors of ion-irradiation-induced dislocation loops, while APT reconstruction of the same region revealed the Cr segregation to these loops. We extended the g•b = 0 invisibility criterion of dislocation loops from TEM mode in a lamella to STEM mode in a needle-shaped specimen. STEM and APT analysis on the same needle provide straightforward correlative analysis, although it is limited by a small observation volume. In contrast, iterative STEM analysis of TEM lamellae, followed by the selective extraction of specific regions of interest for APT analysis, expands the observation area by up to 100 times but requires additional time-consuming steps for APT needle extraction from the lamellae.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Diffusion and Interaction of In and As Implanted into SiO{sub 2} Films

By means of Rutherford backscattering spectrometry, electron microscopy, and energy-dispersive X-ray spectroscopy, the distribution and interaction of In and As atoms implanted into thermally grown SiO{sub 2} films to concentrations of about 1.5 at % are studied in relation to the temperature of subsequent annealing in nitrogen vapors in the range of T = 800–1100°C. It is found that annealing at T = 800–900°C results in the segregation of As atoms at a depth corresponding to the As{sup +}-ion range and in the formation of As nanoclusters that serve as sinks for In atoms. An increase in the annealing temperature to 1100°C yields the segregation of In atoms at the surface of SiO{sub 2} with the simultaneous enhanced diffusion of As atoms. The corresponding diffusion coefficient is D{sub As} = 3.2 × 10{sup –14} cm{sup 2} s{sup –1}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Kinetics of Early Decomposition Stages in Diluted bcc Fe–Сu–Ni–Al Alloy: MC+MD Simulation

A combined approach including the Monte Carlo and molecular-dynamics simulation, decomposition kinetics and segregation formation in the multicomponent low-alloy Fe–1.5Cu–2Ni–1.5Al (at %) alloy is studied. It is shown that the formation of Cu nanoparticles surface-enriched with Ni and Al (coprecipitation mode) includes several stages: (i) the formation of clusters consisting of several Cu atoms, (ii) their enrichment with Ni and Al atoms, and (iii) redistribution of Ni and Al atoms with the formation of a surface layer providing stabilization of Cu nanoparticles. Observed structural features of segregations and their stability in Fe–Cu–Ni–Al alloys is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Photometric and Kinematic Study of the Open Clusters SAI 44 and SAI 45

We carry out a detailed photometric and kinematic study of the poorly studied sparse open clusters SAI 44 and SAI 45 using ground-based BVR {sub c} I {sub c} data supplemented by archival data from Gaia eDR3 and Pan-STARRS. The stellar memberships are determined using a statistical method based on Gaia eDR3 kinematic data, and we found 204 members in SAI 44 while only 74 members are identified in SAI 45. The average distances to SAI 44 and SAI 45 are calculated to be 3670 ± 184 and 1668 ± 47 pc. The logarithmic age of the clusters are determined to be 8.82 ± 0.10 and 9.07 ± 0.10 yr for SAI 44 and SAI 45, respectively. The color–magnitude diagram of SAI 45 hosts an extended main-sequence turnoff (eMSTO). The apparent age spread is found to be similar to the apparent age spread predicted on the basis of the age spread and cluster age relation predicted by rotation models. This indicates that eMSTO is a stellar evolution rather than star formation phenomenon in SAI 45. We conclude that eMSTO in SAI 45 is mainly caused by the different rotation rates of stars as the SYCLIST synthetic population with different rotation rates was able to reproduce the observed eMSTO, and stars in the red part of the eMSTO were preferentially concentrated in the inner region, which again hints at different rotations being the reason for the extension in the upper MS. This finding supports the theory attributing the origin of eMSTO to the different rotations of eMSTO stars. The mass function slopes are obtained as -2.24 ± 0.66 and -2.58 ± 3.20 in the mass rages 2.426–0.990 M{sub ⊙} and 2.167–1.202 M{sub ⊙} for SAI 44 and SAI 45, respectively. SAI 44 exhibits the signature of mass segregation while we found weak evidence of mass segregation in SAI 45 possibly due to tidal stripping. The dynamical relaxation times of these clusters indicate that both clusters are in a dynamically relaxed state. Using the AD-diagram method, the apex coordinates are found to be ([[Formula]], -[[Formula]]) for SAI 44 and (-[[Formula]], -[[Formula]]) for SAI 45. The average space velocity components of the clusters SAI 44 and SAI 45 are calculated in units of km s{sup -1} as (-15.14 ± 3.90, -19.43 ± 4.41, -20.85 ± 4.57) and (28.13 ± 5.30, -9.78 ± 3.13, -19.59 ± 4.43), respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

On the Structure–Property Relationship of Semi‐Coherent FeCr 2 O 4 /Cr 2 O 3 Spinel/Corundum Interfaces

Abstract Oxide heterointerfaces are extremely common in both natural and artificial composite structures, including corroded structural materials. Often, key properties such as segregation and atomic transport are dictated by the structure of these interfaces. However, despite this critical link, very few heterointerfaces have been studied in any detail at the atomic scale. Here, one important oxide heterointerface is examined, between spinel and corundum, using the chemical system FeCr 2 O 4 /Cr 2 O 3 as a representative and technologically important case. Using atomistic simulation techniques, it is found that the structure, particularly the local chemistry, of the interface depends on the crystal chemistry at the interface. This atomic and chemical structure further impacts important properties such as defect segregation and mass transport. It is found that defects can nucleate at some regions of these interfaces and migrate back and forth across the corundum layer, suggesting high atomic mobility that may be important for the evolution of spinel/corundum composite structures in extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Local Multimodal Electro-Chemical-Structural Characterization of Solid-Electrolyte Grain Boundaries

Typical models of polycrystalline ionic materials treat the grain boundary properties as single valued, without consideration of the full range of values that define the macroscopically measured average. Here a unique experimental platform suitable for local multimodal characterization of individual grain boundaries in bicrystal fibers is reported. A variation of three orders of magnitude in the grain boundary conductivity of ceria is observed, as measured across six individual bicrystals by both alternating current impedance spectroscopy and direct current (D.C.) linear sweep voltammetry. Nonlinear behavior of the D.C. measurements is consistent with resistance due to a space charge effect. Time-of-flight secondary ion beam spectroscopy reveals a correlation between grain boundary resistance and the concentration of impurities Si, Al, and Ca segregated at the grain boundaries, although the bulk concentrations of these impurities are negligible. Electron backscatter diffraction analysis of the crystal orientations suggests a correlation between the misorientation across the grain boundaries and grain boundary resistance. These correlations point towards a grain boundary resistance that arises from impurity-generated space charge effects and variations in impurity concentration and hence resistivity driven by the energetics of impurity segregation to grain boundaries of differing surface energies.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electrolyte Effects on the Stability of Ni-Mo Cathodes for the Hydrogen Evolution Reaction

Water electrolysis to form hydrogen as a solar fuel requires highly effective catalysts. In this work, theoretical and experimental studies are performed on the activity and stability of Ni-Mo cathodes for this reaction. Density functional theory studies show various Ni-Mo facets to be active for the hydrogen evolution reaction, Ni segregation to be thermodynamically favorable, and Mo vacancy formation to be favorable even without an applied potential. Electrolyte effects on the long-term stability of Ni-Mo cathodes are determined. Ni-Mo is compared before and after up to 100 h of continuous operation. It is shown that Ni-Mo is unstable in alkaline media, owing to Mo leaching in the form of MoO 4 2- , ultimately leading to a decrease in absolute overpotential. It is found that the electrolyte, the alkali cations, and the pH all influence Mo leaching. Changing the cation in the electrolyte from Li to Na to K influences the surface segregation of Mo and pushes the reaction towards Mo dissolution. Decreasing the pH decreases the OH - concentration and in this manner inhibits Mo leaching. Of the electrolytes studied, in terms of stability, the best to use is LiOH at pH 13. Thus, a mechanism for Mo leaching is presented alongside ways to influence the stability and make the Ni-Mo material more viable for renewable energy storage in chemical bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Grandparent Inference from Genetic Data: The Potential for Parentage-Based Tagging Programs to Identify Offspring of Hatchery Strays

Abstract Fisheries managers routinely use hatcheries to increase angling opportunity. Many hatcheries operate as segregated programs where hatchery-origin fish are not intended to spawn with natural-origin conspecifics in order to prevent potential negative effects on the natural-origin population. Currently available techniques to monitor the frequency with which hatchery-origin strays successfully spawn in the wild rely on either genetic differentiation between the hatchery- and natural-origin fish or extensive sampling of fish on the spawning grounds. We present a method to infer grandparent–grandchild trios by using only genotypes from two putative grandparents and one putative grandchild. We developed estimators of false-positive and false-negative error rates and showed that genetic panels containing 500–700 single-nucleotide polymorphisms or 200–300 microhaplotypes are expected to allow application of this technique for monitoring segregated hatchery programs. We discuss the ease with which this technique can be implemented by pre-existing parentage-based tagging programs and provide an R package that applies the method.

Delomas, Thomas A. (ORCID:000000015154759X)↗
DOE OSTI2019

Organizing thermodynamic data obtained from multicomponent polymer electrolytes: Salt-containing polymer blends and block copolymers

The objective of this review is to organize literature data on the thermodynamic properties of salt-containing polystyrene/poly(ethylene oxide) (PS/PEO) blends and polystyrene-b-poly(ethylene oxide) (SEO) diblock copolymers. These systems are of interest due to their potential to serve as electrolytes in all-solid rechargeable lithium batteries. Mean-field theories, developed for pure polymer blends and block copolymers, are used to describe phenomenon seen in salt-containing systems. An effective Flory–Huggins interaction parameter, χ eff , that increases linearly with salt concentration is used to describe the effect of salt addition for both blends and block copolymers. Segregation strength, χ eff N, where N is the chain length of the homopolymers or block copolymers, is used to map phase behavior of salty systems as a function of composition. Domain spacing of salt-containing block copolymers is normalized to account for the effect of copolymer composition using an expression obtained in the weak segregation limit. The phase behavior of salty blends, salty block copolymers, and domain spacings of the latter systems, are presented as a function of chain length, composition and salt concentration on universal plots. Finally, while the proposed framework has limitations, the universal plots should serve as a starting point for organizing data from other salt-containing polymer mixtures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Toward a standardization of cryostructure and cryogenic soil structure terminology for the field description of permafrost‐affected soils

This paper establishes standardized terminology and field documentation protocols for cryostructures and cryogenic soil structures in permafrost‐affected soils and provides brief guidance on descriptions of ground ice morphology and ice volume estimates. We consolidate permafrost terminology from Russian and North American literature, clarify long‐standing ambiguities, and provide explicit guidelines that align with US Department of Agriculture‐Natural Resources Conservation Service soil description standards. Our scheme makes critical distinctions between cryostructure, the distribution of ice within soil, and cryogenic soil structure, the morphological structure of soil resulting from ice formation. The scheme organizes cryostructures into three main categories: non‐segregated ice, visible segregated ice, and ice matrices. We introduce standardized codes and parameters for field descriptions of ice and soil that enable machine‐readable data collection compatible with existing soil information systems. This standardization will significantly enhance the integration of field observations into landscape‐scale assessments of permafrost stability, infrastructure vulnerability, and ecosystem response to permafrost thaw, addressing an urgent need for quantitative data to inform modeling and decision‐making in rapidly changing Arctic and subarctic environments.

Andersen, Megan L. [University of Minnesota, Saint↗
DOE OSTI2018

Effect of the Milling Conditions on the Properties of ZnO Doped with Fe

(Zn{sub 0.9}Fe{sub 0.1})O powders were produced with different ball to powder weight ratios (BPR) by ball milling of ZnO and Fe elemental powders. The BPR used were 15:1, 20:1, 25:1, and 30:1. The prepared samples were studied by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectroscopy (MS). The XRD patterns showed a zinc oxide (ZnO) single phase with wurtzite structure, except for the 15:1 ratio, which exhibits an additionally bcc structure associated to α-Fe. The mean crystallite sizes were found to be around 100 Å. The Mössbauer spectra were fitted using two doublets, associated to the incorporation of Fe ions into the ZnO lattice, which correspond to the Fe{sup 3+} and Fe{sup 2+} oxidation states except for the 15:1 ratio, for which an additional sextet was necessary to obtain a good fit, this sextet was associated to segregated Fe into the sample. The increase of the BPR allowed that all Fe penetrated into the ZnO matrix. The magnetization measurement using VSM reveals that the system exhibits ferromagnetic behavior at room temperature. For sample with BPR 15:1, the ferromagnetism is due to the segregated Fe, and for higher BPRs, from 20:1 up to 30:1, we propose that their ferromagnetism is due to the percolation of polarons. These polarons appear due to the oxygen vacancies (detected by XRD) which are occupied by electrons, which appear in the charge balance. Exchange interaction between the electron spins located in the vacancies or holes and those of the magnetic impurities (Fe atoms) leads to the formation of bound magnetic polarons, which percolate, producing in this way magnetic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

A Mechanism for Carbon Depletion at Bondline of High-Frequency Electric-Resistance-Welded X70 Pipeline Steel

The bondline of electric-resistance-welded (ERW) linepipe steel, often etched white (i.e., ferrite) in optical microscopy, is generally believed to be carbon depleted. The mechanism for the carbon depletion, however, is not fully understood by researchers. To this end, here we used atom probe tomography (APT) to measure elemental segregation of the as-welded and post-weld heat-treated bondline regions of X70 linepipe welds. The thin vertical features at the bondline in the as-welded condition were identified as carbon-rich martensite-austenite (M-A) constituents, and the majority ferrite phase in the bondline was identified as carbon-depleted ferrite. Following the post-weld normalization, all alloying elements, except Nb and Mo, are homogenized across the bondline and heat-affected zone. The carbon depletion in the ERW bondline was accurately measured. A new mechanism for carbon depletion has been proposed using Scheil calculations of elemental partitioning during weld formation. Segregation of elements in the heat-affected zone was shown to follow the negligible partitioning local equilibrium (NPLE) kinetics for bainite transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Thermodynamics and Kinetics of Refractory Multi-principal Element Alloys: An Experimental and Modeling Comparison

Here, the search for structural alloys capable of ultrahigh temperature performance has led to the exploration of refractory multi-principal element alloys (RMPEAs). In this work, experimental results for solidification segregation and homogenization of two RMPEAs, NbTaTiW and MoNbTaTi, are compared to simulations using the Scheil and DICTRA modules in Thermo-Calc®. Scheil calculations accurately predict the observed solidification segregation, while DICTRA predicts general trends and can provide a minimum time to achieve homogenization at a given temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of Particle Spreading Dynamics on Powder Bed Quality in Metal Additive Manufacturing

Powder spreading precedes creation of every new layer in powder bed additive manufacturing (AM). The powder spreading process can lead to powder layer defects such as porosity, poor surface roughness and particle segregation. Therefore, the creation of homogeneous layers is the first task for optimal part printing. Discrete element methods (DEM) powder spreading simulations are typically limited to a single layer and/or small number of particles. Therefore, results from such model configurations may not be generalized to multiple layer processes. In this study, a computationally efficient multi-layer powder spreading DEM simulation model is proposed. The model is calibrated experimentally using static Angle of Repose measurements. The adhesion model parameter, cohesive energy density is related to adhesive surface energy and strain energy release rate parameters. The model results show that interaction between particle and the powder spreading rake leads to noticeable variation in packing density, surface roughness, dynamic angle of repose (AOR), particle size distribution, and particle segregation. Finally, the powder model is experimentally validated using a recoater spreading rig to measure the dynamic AOR at spreading speeds consistent with recoating speeds and layer heights used in AM processes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The synergistic role of Mn and Zr/Ti in producing θ'/L12 co-precipitates in Al-Cu alloys

Microstructural stability is a critical factor to consider when designing new alloys for high-temperature applications. An Al-Cu alloy with Mn and Zr additions has recently been developed to withstand extended exposures of up to 350 °C. The addition of Mn in combination with Zr and their segregation to precipitate interfaces play a significant role in stabilizing the metastable θ ' precipitates responsible for the alloy's hardness; however, adding Zr and Mn separately only improves the stability to 200 °C and 300 °C, respectively. To this end, the effect of the synergistic additions on interfacial structure and chemistry was studied in detail using atom probe tomography (APT) and scanning transmission electron microscopy (STEM) for Al-Cu-Mn-Zr/Ti-containing alloys subjected to long-term annealing (up to 2,100 h) in the critical temperature range, 300 °C and 350 °C, to investigate the role of Zr/Ti in increasing the θ '-precipitate stability. The APT and STEM results reveal that Mn additions stabilize θ ' long enough for the slower diffusing Zr atoms to segregate to coherent θ ' interfaces that eventually create a θ '/ L1 2 -Al 3 (Zr x ,Ti 1-x ) co-precipitate structure. The co-precipitate is highly stable, as shown by density functional theory calculations, and is a key factor that governs microstructural stability beyond 300 °C. This study reveals how solute additions with different stabilization mechanisms can work in concert to stabilize a desired microstructure, and the results provide insights that can be applied to other high-temperature alloy systems.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Role of interfaces on phase formation during severe plastic deformation

The role of interfaces on phase formation during severe plastic deformation (SPD) was investigated using molecular dynamics simulations. It is found that dilute solute additions that segregate to interphase boundaries, and strengthen them, can greatly extend the solubility limits of the bounding phases at steady state, providing a novel approach to processing nanocomposite alloys by SPD. Here, the results are rationalized in terms of a modified effective temperature model, whereby increasing the interface strength leads to higher effective temperatures and correspondingly to higher solubilities. Comparison of the segregation coefficient at the interphase boundary with solubilities in the bounding phases illustrates the effective temperature model is self-consistent and comprehensive. Past experimental studies on severe plastic deformation are found consistent with these observations.

36 MATERIALS SCIENCE↗
DOE OSTI2026

High temperature stabilization of ultrafine grain tungsten alloys through synergistic compositional complexities

Thermally-stabilized fine-grained microstructures in tungsten provide a pathway to harnessing enhanced properties such as a reduced ductile-to-brittle transition temperature and improved strength while mitigating the adverse effects of grain growth and recrystallization. Here, in this study, we employ a material design strategy that relies on grain boundary segregation in the nanocrystalline state driven by alloy thermodynamics balanced with impurity scavenging through in situ formation of kinetically-stabilizing metal carbides. A W-Ti-Cr alloy is designed through lattice Monte Carlo methods and subsequently synthesized in a single-phase nanocrystalline state, which upon annealing, evolves into an ultrafine grained microstructure containing chromium grain boundary segregation collectively with a dispersed TiX (X=C,O) phase through the reaction of titanium with carbon and oxygen impurities. In situ synchrotron X-ray diffraction experiments demonstrate that increased Ti promotes stabilization across a larger temperature range but with diminishing returns above 10 at.% Ti. Long-term stability was confirmed through the retention of the ultrafine grained microstructure for a total of 8 days (192 h) at 1300 °C without grain/carbide growth and/or recrystallization. Our results demonstrate that, through strategic tailoring of composition and microstructure, one can harness the benefits of both thermodynamic and kinetic stabilization mechanisms, opening pathways for future alloy formulations that expand the window of stability.

36 MATERIALS SCIENCE↗