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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

High Resolution Mapping of Orientation and Strain Gradients in Metals by Synchrotron 3D X-ray Laue Microdiffraction

Synchrotron 3D X-ray Laue microdiffraction, available at beamline 34-ID-E at Advanced Photon Source in Argonne National Laboratory, is a powerful tool for 3D non-destructive mapping of local orientations and strains at sub-micron scale in the bulk. With this technique, it is possible to study local residual stresses developed during manufacturing or while in service due to interactions between, for example, different phases and/or grains with different orientations in materials containing multiple or single phase(s). Such information is essential for understanding mechanical properties and designing advanced materials, but is largely non-existent in the current generation of materials models. In the present paper, the principle and experimental set-up of the 3D microdiffraction are introduced, followed by a description of a method for quantification of the local plastic deformation based on high-angular-resolution orientation maps. The quantification of local residual stresses in two model materials, ductile cast iron (two phases) and partially recrystallized pure nickel (single phase), using 3D microdiffraction will then be presented. The results show that 3D microdiffraction is important for understanding the origin of local residual stresses and to relate them to the microstructural evolution. Finally, the limitations of the 3D microdiffraction on the current generation synchrotron source and new possibilities after the synchrotron upgrade are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Formation Mechanism of Nanoscale Al{sub 3}Fe Phase in Al-Fe Alloy During Semisolid Forming Process

The formation mechanism of nanoscale Al{sub 3}Fe phase in Al-1Fe (wt pct) alloy during rheo-extrusion was investigated, and the mechanical property of the prepared alloy was also measured. The results show that the average length of Al{sub 3}Fe phase in Al-1Fe alloy prepared by rheo-extrusion is 300 nm, which is much more refined than the needlelike Al{sub 3}Fe phase in as-cast Al-1Fe alloy (50 μm). In rheo-extrusion, Al{sub 3}Fe phase formed by eutectic reaction is bonelike, but it could be continuously refined by the shear deformation in the wheel groove, in equal channel angular flow, and in expansion extrusion mold. The total equivalent strain of the shear deformation is higher than 4.82. The tensile strength and elongation of Al-1Fe alloy prepared by rheo-extrusion are 135 MPa and 30 pct, respectively. The tensile strength of Al-1Fe alloy prepared by rheo-extrusion is 58.8 pct higher than that of as-cast Al-1Fe alloy, and the elongation is 19 pct higher than that of as-cast Al-1Fe alloy. Compared with as-cast Al-1Fe alloy, the improvements of tensile strength and elongation caused by shear deformation in rheo-extrusion are higher than the reported improvements induced by rare earth modification.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Angular momentum of fission fragments from microscopic theory

During nuclear fission, a heavy nucleus splits into two rotating fragments. The associated angular momentum is large, yet the mechanism of its generation and its dependence on the mass of fragments remain poorly understood. In this Letter, we provide the first microscopic calculations of angular-momentum distributions in fission fragments for a wide range of fragment masses. For the benchmark case of 239 Pu(n th ,f), we find that the angular momentum of the fragments is largely determined by the nuclear shell structure and deformation, and that the heavy fragments therefore typically carry less angular momentum than their light partners. We use the fission model freya to simulate the emission of neutrons and photons from the fragments. The dependence of the angular momenta on fragment mass after the emission of neutrons and statistical photons is linear for the heavy fragments and either constant or weakly linear for the light fragments, consistent with the universal sawtooth pattern suggested by recent experimental data. Finally, we observe that using microscopic angular-momentum distributions modifies the number of emitted photons significantly.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Effect of equal channel angular pressing on the mechanical and tribological behavior of Al-Zn-Mg-Cu alloy

Highlights: • The correlation of microstructure, mechanical and wear properties has been studied. • The correlation between tensile properties and shear properties has been also studied. • Mechanical and tribological properties have been improved through the ECAP process of the Al-7075 alloy. • The dominant wear mechanisms in the initial material were adhesive and oxidative wear as well as delamination. • Abrasive and oxidative wear were the dominant wear mechanisms in ECAP processed specimens. - Abstract: Microstructure, mechanical properties and wear behavior of severely deformed Al-7075 alloy by equal channel angular pressing (ECAP) were studied. Microhardness, tensile and shear strength tests were performed to evaluate the mechanical properties of the material. The relationship between tensile and shear strength was also extracted. In addition, with the aim of study the wear behavior, the wear tests were performed by using a pin-on-disk machine under different normal loads. The microscopic observations i.e. transmission electron microscopy (TEM) and scanning electron microscope (SEM), were used to analyze the microstructure of specimens as well as the surface, subsurface and debris of worn specimens. Mechanical properties results showed that the hardness and strength (tensile and shear) of the ECAP-processed alloy were higher than that of the annealed alloy and increased with the increment of pass number. The wear test data revealed that the wear rate and friction coefficient decreased with increasing ECAP passes. The SEM analysis of worn specimens demonstrated that the dominant wear mechanisms of the annealed alloy were adhesion wear and delamination and the dominant wear mechanisms of ECAP processed alloy were abrasive wear and plowing bands. Oxidative wear was also observed at both annealed and ECAPed alloy. Totally, these results demonstrated that ultrafine-grained structure fabricated by ECAP, improves the wear resistance of the Al-7075 alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nuclear states projected from a pair condensate

Atomic nuclei exhibit deformation, pairing correlations, and rotational symmetries. To meet these competing demands in a computationally tractable formalism, we revisit the use of general pair condensates with good particle number as a trial wave function for even-even nuclei. After minimizing the energy of the condensate, allowing for general triaxial deformations, we project out states with good angular momentum with a fast projection technique. To show applicability, we present example calculations from pair condensates in several model spaces and compare against angular-momentum projected Hartree-Fock and full configuration-interaction shell-model calculations. This approach successfully generates spherical, vibrational, and rotational spectra, demonstrating potential for modeling medium- to heavy-mass nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Nucleon-Pair Shell Model within a Symmetry Broken Basis

The nucleon-pair shell model (NPSM) within the framework of a broken symmetry basis is studied. The results demonstrate the validity of such a scheme, which in turn leads to a significant reduction in the dimensionality of the multi-pair configuration space. Specifically, in the case of an axially-deformed basis, the results yield a satisfactory description of the low-lying spectrum, even without the need for applying the projection procedure. In the case of a triaxially-deformed basis, the result of variation after angular momentum projection suggest a potential for using the NPSM to find exact solutions in a semi-magic system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Microstructure evolution and mechanical performance of copper processed by equal channel angular rolling

Highlights: • Copper was processed by equal channel angular rolling (ECAR) up to 33 passes. • A very fine grained microstructure with high dislocation density was developed. • A decrease of dislocation density was observed for high numbers of passes. • The proof stress saturated at a value of about 400 MPa. • ECAR is a possible way of commercialization of ultrafine-grained materials. - Abstract: Ultrafine-grained (UFG) oxygen free high conductivity (OFHC) Cu samples were processed by severe plastic deformation (SPD) using the method of equal channel angular rolling (ECAR) up to 33 passes at room temperature. It was found that the grain size gradually decreased from ~ 40 μm to ~ 250 nm with increasing the number of passes. A maximum dislocation density of ~ 21 × 10{sup 14} m{sup − 2} was achieved after 13 passes of ECAR. For large numbers of passes (between 23 and 33), the dislocation density decreased to ~ 14 × 10{sup 14} m{sup − 2}. The proof stress was saturated at the value of about 400 MPa. The stored energy was measured by calorimetry and compared with the values calculated from the parameters of the microstructure. The reduction of the released heat after 13 and 33 passes suggested structural relaxation of the UFG microstructure. For these numbers of passes, the reduction of area in tensile testing was improved without decreasing the proof stress. The correlation between the microstructure and the mechanical behavior was discussed in detail. It was found that ECAR is capable for the mass-production of UFG metallic materials with high strength, therefore this method is a possible way of commercialization of SPD-processed materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure of titanium on complex deformation paths: Comparison of ECAP, KOBO and HE techniques

Highlights: • Method for producing CP titanium rods for medical implants is searched. • Three processing methods producing ultra-fine grain titanium are compared. • Microstructure and textures are examined and analysed. • Mechanical characteristics are determined based on microhardness and tensile tests. • Hydrostatic extrusion (HE) leads to the best properties of titanium rods for medical implants. - Abstract: In this work samples of commercial purity grade 2 titanium were severely deformed by three different extrusion techniques: equal-channel angular pressing (ECAP), extrusion through oscillating die (KOBO), and hydrostatic extrusion (HE). Resulting microstructures and mechanical properties of processed titanium samples are studied and compared with regard to potential application as a material for dental implants. The obtained results demonstrate the effect of different strain paths, involved by three applied deformation methods, on microstructure refinement, mechanical properties and textures of the studied material. Heterogeneous microstructures with bimodal grain size distributions are observed for all deformation techniques in the examined material, however differences in their internal structures and grain boundary distributions point to different grain refinement mechanisms. The fraction of ultra-fine grains is the highest in titanium deformed by HE. Also the internal grain fragmentation is the most important after HE deformation. This leads to the best mechanical and microstructural properties obtained in this type of deformation. Consequently, the HE process seems to be very interesting for production of material for medical implants.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nucleon-pair approximation for nuclei from spherical to deformed regions

Here we model low-lying states of atomic nuclei in the nucleon-pair approximation of the shell model, using three approaches to select collective nucleon pairs: the generalized seniority scheme, the conjugate gradient method, and the Hartree-Fock approach. We find the collective pairs obtained from the generalized seniority scheme provide a good description for nearly spherical nuclei, and those from the conjugate gradient method or the Hartree-Fock approach work well for transitional and deformed nuclei. Our NPA calculations using collective pairs with angular momenta 0, 2, and 4 (denoted by S D G pairs) reproduce the nuclear shape evolution in the N = 26 isotones, Ca 46 , Ti 48 , Cr 50 , and Fe 52 , and yield good agreement with full configuration-interaction calculations of low-lying states in medium-heavy transitional and deformed nuclei: Ti 44 – 48 , Cr 48 , Cr 50 , Fe 52 , Zn 60 – 64 , Ge 64 , 66 , Mo 84 , and Xe 108 – 112 . Finally, using the S D G I -pair approximation we describe low-lying states of Ba 112 , 114 , cases difficult to reach by conventional configuration-interaction methods.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

In-situ synchrotron X-ray micro-diffraction investigation of ultra-low-strain deformation microstructure in laminated Ti-Al composites

An ultra-low-strain deformation microstructure was revealed for the first time non-destructively in the bulk interior of an annealed laminated Ti-Al composite-in the "fully recrystallized" Al layer-by a synchrotron-based micro-diffraction technique, namely differential aperture X-ray microscopy (DAXM), through real space mapping with a very high angular resolution (0.01 degrees). This ultra-low-strain deformation microstructure was found to result from the thermal stress, induced during cooling after annealing, due to the different coefficients of thermal expansion for the Ti and Al layers. The annealed sample was further tensile deformed to a strain of 1.66% and followed by in situ DAXM and analyzed by various misorientation mapping methods. The results pointed to the important effects of the initial microstructure and the interface constraint, as well as the grain size and crystal orientation, on the plastic deformation. A gradient in dislocation density from the layer interface to the center was found in the Al layer of the annealed sample, and this gradient increased slightly during tensile deformation. The variation of the dislocation density was further discussed based on the activation and interaction of dislocations in grains of different sizes and orientations during plastic deformation. The findings of this study provided valuable insights in understanding the constraint effect of the laminated metal composite and the design of novel composite materials. (c) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Crystallographic orientation↗
DOE OSTI2023

Minor titanium addition markedly improves the co-deformability of copper-tantalum composites

We investigated the microstructures of equal channel angular extrusion (ECAE) processed sintered composites of copper (Cu) and tantalum (Ta). These composites were produced with nominal Ta volume percentages ranging from 25% to 75%. Additional composites of the same nominal Ta content were prepared with a minor amount of titanium (Ti) added to facilitate interphase bonding. Ti addition was found to markedly improve the strength and co-deformability of the composites, allowing reliable extrusion of Cu-Ta composites with novel microstructures. A major influence of the Ti appears to be to soften the Ta, which contributes to improved co-deformability by reducing the flow stress mismatch between the composite constituents. Here, a change in the fracture surface morphology in the Ti-modified composite compared to the unmodified composite suggests that the Ti may also improve cohesion between Cu and Ta by reducing Ta surface oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Workability Limits of Magnesium Alloy AZ31B Subjected to Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is an important severe plastic deformation process to produce ultrafine grained microstructures in metals and alloys. Magnesium and its alloys generally possess poor workability at temperatures below 250 °C. This investigation examines the influence of different passes and processing routes of ECAP on improving the workability of Mg alloy AZ31B. ECAP was carried out for three passes using a die of angle 120° using processing routes Bc and C. The operating temperature was 523 K for the first pass and 423 K for the subsequent two passes. The resultant microstructure and mechanical properties were determined. Workability of the alloy at 423 K (150 °C) was determined using upsetting experiments on cylindrical specimens machined from the annealed and ECAPed samples. Workability limit diagrams have been constructed for the various processed conditions. The workability data generated were also analyzed using five different workability criteria (also referred to as ductile fracture models) and the material constants for these five models were evaluated. Specimens processed by two passes through route C (pass 2C) exhibits better workability compared to other passes since the workability limit line after this pass shows maximum safe working area and lies above the other workability lines. Among the five different workability criteria investigated, the Freudenthal workability criterion is more suitable for prediction of failure in this alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Microscopic description of the torque acting on fission fragments

When two fragments are created in a fission decay, any torque due to nuclear and Coulomb interaction can change the fragment's angular momentum. This paper explores the character and magnitude of the angular momentum as a function of the initial conditions around the scission point using the time-dependent Hartree-Fock theory. To understand the torque acting on the fragments, the Frozen Hartree-Fock method is also used to determine the collective potential at scission. Two 240 Pu fission channels ( 132 Sn + 108 Ru and 144 Ba + 96 Sr) are studied. Further, these two channels cover different shapes (spherical, quadrupole, and octupole deformation) of the fragments. It is found that the angular momentum generated by the Coulomb interaction after fission is mainly collective, while this is not the case for the angular momentum generated at scission. The competition between rotational modes (bending, wriggling, and twisting) is discussed and shows that the angular momentum is generated mainly perpendicular to the fission axis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Self-Organization of Multiscale Structural Groups in a Low-Carbon Wire Subjected to Severe Drawing

The peculiarities of the mechanical parameters and atomic structure of wires made of 08G2S steel subjected to severe drawing with a combination of shear and classical circular drawing of different diameters. The split form of interference maximums (211) in X-ray diagrams of samples is evidence for delamination in families of the mentioned planes into contracted and extended groups, which is accompanied by the partial order–disorder phase transition with formation of the amorphized fraction from fragments of nanosized atomic groups of these planes (clusters). The dependence on steel deformation revealed the nature of the change in the symmetry of the distribution of structural groups relative to the angular position of the diffraction maximum from the planes (211). It is established that with increased deformation (ε > 30%) the intensities of coherent and incoherent X-ray CrK{sub α}-emissions vary quantitatively, which proves the development of self-organizing processes contributing to the increase in the volume fraction of the order relative to the disorder in 08G2S steel, even subject to severe mechanical loading.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Seamless Nb tubes for SRF cavities

A. Executive Summary Understanding Developed Relationships between level of work, plastic strain orientation, level of annealing, grain size, strength, ductility, and texture were developed for heavily worked bulk RRR grade cast pure niobium (Nb). Technical Effectiveness of Approach Part A: The approach used for plastic deformation of bulk Nb was room temperature equal channel angular extrusion (ECAE). This approach is very effective for microstructural breakdown of worked and post-strain recrystallized Nb. A major problem with breaking down the microstructure of cast Nb is development of a consistent (repeatable) and uniform microstructure. This is most effectively accomplished by a series of orthogonal working steps (multipass ECAE (mECAE)) separated by full recrystallization. Forming tube from such material leads to a uniform microstructure in the tube. Part B: The approach developed to produce a microstructure in thin-walled tube that is very favorable for hydroforming into a superconducting radio frequency (SRF) cavity is tube-ECAE (tECAE). Tube-ECAE results in an axisymmetric circumferentially uniform microstructure with a texture more favorable for expansion hydroforming than tube formed by conventional methods such as extrusion, drawing, and ironing. Economic Feasibility of Methods Investigated and Demonstrated Although this was not demonstrated because of funding limitations, it is strongly believed that mECAE combined with intermediate recrystallization heat treatments and tECAE are economically viable approaches for producing a consistent, uniform, fine- or coarse-grained microstructure in RRR grade Nb tube starting from a large-grained and highly textured cast ingot. These methods are relatively easy to apply; the challenge is development of equipment and tooling that works well and is operator friendly. Commercially viable ECAE tooling for bulk Nb microstructure breakdown was developed; significant progress was made on the design of scaled-up equipment for tECAE. Patents on tECAE have been granted in Europe, Japan, and the United States. Public Benefit The approaches developed for fabricating RRR grade Nb tubing suitable for hydroforming into multi-cell SRF cavities have substantial public benefit because they will enable the manufacture of lower cost multicell SRF cavities for advanced linear particle accelerators. In addition, the approach developed for fabricating uniform and consistent axisymmetric microstructures in metal tubing can be applied to tubes made of metal alloys other than Nb. Applications exist in Ta tubing for superconductor wire applications, Mg alloy tubing for bio-implants, and aerospace tubing for structural hollow section components. The idea of tECAE can be applied to heal the heat affected zone (HAZ) in seam-welded tubing, thus erasing or healing the low-strength properties in the weld zone.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Achieving Grain Refinement and Related Mechanical Property Improvement of an Al-Zn-Mg-Cu Alloy Through Severe Plastic Deformation

Microstructural features and mechanical properties of an Al-Zn-Mg-Cu alloy processed by equal-channel angular pressing (ECAP) have been investigated. The equivalent plastic strain obtained from the simulation agrees well with that from the analytical calculation in a way that both increase with an increase in deformation, but the strain distribution is non-uniform, appearing as a strain gradient along the norm direction. Microstructure investigation shows that grain refinement is achieved in frequency of low-angle grain boundaries fabricated by ECAP. The pole density is reduced by ECAP, during which the Brass and Goss type textures are introduced. TEM results show chain-like recrystallized grains formed at the grain boundaries and broken second-phase particles come into being due to the heavy shear force. After ECAP, the hardness and strength increase significantly while the elongation is reduced. Besides, an extreme strengthening is confirmed because of the balance between dynamic hardening and softening. The microstructure evolution mechanism is revealed in terms of grain refinement, precipitate phase breakage and texture evolution.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Diagenesis is key to unlocking outcrop fracture data suitable for quantitative extrapolation to geothermal targets

Exceptionally large, well-exposed sandstone outcrops in New York provide insights into folds, deformation bands, and fractures that could influence permeability, heat exchange, and stimulation outcomes of geothermal reservoir targets. Cambrian Potsdam Sandstone with <5% porosity contains decimeter-scale open, angular-limbed monoclines <0.5 km apart with associated low-porosity mm-wide cataclastic deformation bands. Crossing and abutting relationships among sub-vertical opening-mode fractures show four chronological Sets A–D, striking NNW, NE, NW, and ENE, respectively. Fracture lengths and heights range from millimeters to tens of meters. Sets A and C macro-fractures, and possibly B and D, contain quartz deposits. All sets have abundant associated quartz cemented microfractures that also record set orientations and crosscutting relations. Quartz cement deposits—evidence of diagenesis—are the key to identifying attributes of outcrop fractures suitable for extrapolation to geothermal targets in sandstones because they show which fractures formed in the subsurface. Set A fluid inclusion homogenization temperatures (120°C–129°C) are compatible with fracture at >3 km depth. Fractures are stiff and those ≥0.05 mm (Set C) and ≥0.1 mm (Set A) are open and potentially conducive to flow. Sets A and D are abundant in outcrops with close fracture spacing—0.18 m and 0.68 m, respectively—and define a rectangular connectivity network dominated by crossing and abutting X and Y nodes. Set A aperture distributions follow a power law with slope –0.8 up to 0.15 mm; other sets have lognormal distributions. Set A and D microfractures are weakly clustered, while macro-fractures commonly have 1D anticlustered (regular or periodic) arrangements at shorter length scales (<0.2 m). Sub-horizontal fractures are barren and may have formed near the surface. Fracture heights, lengths, and spatial arrangements show good trace connectivity but low open connectivity. For geothermal applications, outcrop results predict low initial well-test permeabilities owing to quartz disconnecting open fractures, but stimulation of closely spaced microfractures and partly open macro-fractures could yield high surface area for heat exchange. Quantitative extrapolation of key fracture attributes like abundance, orientation, spatial arrangement, length, and open fracture connectivity is possible from outcrops to fractured reservoirs if differing thermal histories and diagenesis are accounted for.

02 PETROLEUM↗
DOE OSTI2020

Anisotropic Motions of Fibrils Dictated by Their Orientations in the Lamella: A Coarse-Grained Model of a Plant Cell Wall

Plant cell walls are complex systems that exhibit the characteristics of both rigid and soft material depending on their external perturbations. The three main polymeric components in a plant primary cell wall are cellulose fibrils, hemicellulose, and pectins. These components interact in a hierarchical fashion giving rise to mesoscale structural features such as cellulose bundles, lamella stacking, and so on. Although several studies have focused on understanding these unique structural features, a clear picture linking them to cell wall mechanics is still lacking. As a first step toward this goal, a phenomenological model of plant cell wall has been developed in this work by using available experimental data to investigate the underlying connections between mesoscale structural features and the motions of fibrils during deformation. In this model cellulose fibrils exhibit motions such as angular reorientations and kinking upon forced stretching. Furthermore, these motions are dependent on the orientation of fibrils with respect to the stretch direction, i.e., fibrils that are at an angle to the stretch direction exhibit predominant angular reorientations, while fibrils transverse to the stretch direction undergo kinking as a result of transverse compression. Varying the chain length of pectin had negligible effects on these motions. One of the main contributions from this work is the development of a simple model that can be easily fine-tuned to test other hypotheses and extended to include additional experimental knowledge about the structural aspects of cell walls in the future.

36 MATERIALS SCIENCE↗