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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Machine learning technique to identify grains in polycrystalline materials samples

A method of identifying grains in polycrystalline materials, the method including (a) identifying local crystal structure of the polycrystalline material based on neighbor coordination or pattern recognition machine learning, the local crystal structure including grains and grain boundaries, (b) pre-processing the grains and the grain boundaries using image processing techniques, (c) conducting grain identification using unsupervised machine learning; and (d) refining a resolution of the grain boundaries.

Sankaranarayanan, Subramanian↗
DOE OSTI2024

A computational study of the effects of graphene additions on electrical properties of polycrystalline copper

The addition of graphene has recently shown promise as a route for the significant improvement of the bulk electrical properties of metallic materials. Here, we explore the effects these additions have on the net electrical conductivity of fabricated copper-graphene (Cu-Gr) nanocomposites as a function of grain structure and grain boundary properties. Synthetic 3D microstructures were generated to represent polycrystalline copper with different average grain diameters and twinned grain boundary fractions. Then, the Poisson equation of electrical transport was solved using a finite difference method in order to predict the net electrical conductivity of each microstructure. In this context, the potential effect of graphene on the conductivity of the composite was evaluated as a function of the number of affected grain boundaries. The results of these calculations indicate that 1.) as supported by literature, net electrical conductivity decreases with decreasing grain size, 2.) the presence of twinned grain boundaries results in smaller loss of conductivity than would otherwise be expected, and 3.) the presence of graphene on the grain boundaries can be expected to lead to improvements in net electrical conductivity. However, we also find that 4.) when the Cu grain structure becomes sufficiently refined, the addition of graphene could conceivably result in significant improvements in electrical conductivity over and above coarse-grained Cu. It is estimated from our calculations that, assuming microstructures with average grain sizes between 100 nm and 100 μm and graphene conductivity 1000 to 10,000 that of a typical Cu grain boundary, an improvement in electrical conductivity of approximately 17% over that of bulk Cu may be attainable. Therefore, by performing this study we suggest a possible route for the improvement of Cu electrical properties through the addition of graphene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The structure of sc16 GaP obtained at 17.5 GPa and 1400 K

We report using a laser-heated diamond anvil cell, a powdered sample of gallium phosphide was compressed to 17.5 GPa and heated up to 1400 K. The material obtained was characterized at room temperature using synchrotron x-ray diffraction. Experimental results were compared with first-principles calculations. The polymorph observed assumes the simple cubic structure (sc16) initially reported for GaAs at high pressures. Microdiffraction mapping showed variable grain sizes of the synthesized phase, with the largest grains located in the middle of the heated spot. Structural refinements were performed on selected grains. The structure predicted based on first-principles calculations is in close agreement with the experiments. The two Ga–P bonds show similar lengths in sc16-GaP; however, the bond angles differ, resulting in a distorted tetrahedral coordination geometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

An additively manufactured AlCuMnZr alloy microstructure and tensile mechanical properties

In this study, selective laser melting (SLM) was used to fabricate an AlCuMnZr alloy. The microstructural features that resulted from additive manufacturing (AM) were significantly refined compared to the corresponding cast alloy features. A combination of fine equiaxed and columnar grains along with in-situ formation of θ' precipitates during AM leads to enhanced yield strength (up to 300°C) in the as-fabricated AM alloy. The refinement of brittle intermetallics and a bimodal grain size distribution leads to improved tensile elongation in the AM alloy. The results illustrate the microstructural advantages that can result from additive processing over conventionally processed microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Crafting Multifunctional Materials with Tailored Mechanical and Magnetic Properties by Solid-State Non-equilibrium Processing

Aluminum matrix composites hold promise for creating lightweight structural components with multifunctional properties. Nonetheless, achieving desired magnetic or electrical characteristics without compromising their fundamental mechanical properties presents a significant challenge. Here, in this study, we explore mechanical stir-based extrusion as a solid-state metalworking technique to develop fine-grained microstructures and highly refined metallic composites. Our study focuses on creating a SmCo 5 -reinforced aluminum matrix composite using solid stir extrusion (SSE) and assessing its microstructure, mechanical, and magnetic properties through a comprehensive suite of characterization tools, including x-ray diffraction, electron microscopy, and magnetometry. Our findings reveal that incorporating a small amount (3.76 wt.%) of SmCo 5 phase in a non-heat-treatable, non-magnetic aluminum alloy via SSE yields a composite that exhibits good hard magnetic characteristics with a large coercivity (H ci = 13.5 kOe) and improved mechanical properties. This study underscores non-equilibrium processing via solid-state high-speed stirring as a compelling method for crafting multifunctional materials with tailored mechanical and magnetic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Process-Structure-Property Relations for As-Deposited Solid-State Additively Manufactured High-Strength Aluminum Alloy

Solid-state additive manufacturing methods provide innovative solutions to circumvent problems associated with materials susceptible to hot cracking by avoiding liquid solid phase transformations. In this work, the process parameter influence on microstructural evolution and mechanical response of a fully dense aluminum alloy 7050 (AA7050) component manufactured via a rapid, solid-state additive manufacturing process known as Additive Friction Stir Deposition (AFS-D) was quantified for the first time. Three sections (starting dwell, transient, crossover of roads) of the deposition that exhibit differing thermomechanical processing histories were evaluated for the resulting microstructure and mechanical response. The microstructural characterization was performed on the as-deposited AA7050 via Electron Backscatter Diffraction (EBSD), TEM, optical microscopy, and Scanning Electron Microscopy (SEM). The microstructural characterization revealed refined constituent particles and grains throughout the as-deposited AA7050 microstructure. Furthermore, quasi-static tensile experiments were conducted in both the build and transverse directions, in order to quantify the orientation influence on tensile properties of the as-deposited AA7050 build. Spatially dependent tensile properties were observed in the material due to heat input variation coarsening of secondary phases towards the initial layers of the AFS-D build. Post-mortem analysis revealed that voids nucleated and coalesced from the overgrowth of the strengthening precipitates present in the material, resulting in fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Exceptional strength and wear resistance in an AA7075/TiB 2 composite fabricated via friction consolidation

The friction consolidation method successfully reinforced aluminum 7075 alloy (AA7075) with high-volume fractions (12 and 24 vol%) of titanium diboride (TiB 2 ) by high pressure and severe plastic deformation at elevated temperatures. The consolidated AMCs have a uniform dispersion of submicron- and micron-sized TiB 2 particles in the AA7075 matrix, with significant refinement of the matrix grain size and the particles. The addition of TiB 2 significantly increases hardness by up to 50 %, Young’s modulus by up to 62 %, and ultimate tensile strength by up to 28 % to 672 MPa, while reducing ductility by 80 %. Wear resistance of 7075/24 vol% TiB 2 improves seven-fold compared to baseline, making it comparable to that of carburized steels. Microstructure-based finite element modeling provided a theoretical strength limit of ~730 MPa for the composites and indicated that high triaxiality in conjunction with severe equivalent plastic strain in a narrow area between the TiB 2 particles led to early fracture initiations, limiting the ductility.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Analysis of Interpretable Data Representations for 4D-STEM Using Unsupervised Learning

Abstract Understanding the structure of materials is crucial for engineering devices and materials with enhanced performance. Four-dimensional scanning transmission electron microscopy (4D-STEM) is capable of mapping nanometer-scale local crystallographic structure over micron-scale field of views. However, 4D-STEM datasets can contain tens of thousands of images from a wide variety of material structures, making it difficult to automate detection and classification of structures. Traditional automated analysis pipelines for 4D-STEM focus on supervised approaches, which require prior knowledge of the material structure and cannot describe anomalous or deviant structures. In this article, a pipeline for engineering 4D-STEM feature representations for unsupervised clustering using non-negative matrix factorization (NMF) is introduced. Each feature is evaluated using NMF and results are presented for both simulated and experimental data. It is shown that some data representations more reliably identify overlapping grains. Additionally, real space refinement is applied to identify spatially distinct sample regions, allowing for size and shape analysis to be performed. This work lays the foundation for improved analysis of nanoscale structural features in materials that deviate from expected crystallographic arrangement using 4D-STEM.

Bruefach, Alexandra (ORCID:0000000209323477)↗
DOE OSTI2022

Nanostructure refinement and phase formation of flash annealed FeNi-based soft magnetic alloys

In this work, the resulting nanocomposite microstructures of FeNi nanocrystallites under different heating and cooling rates (5 °C/min vs 400-500 °C/s) is investigated. Conventional furnace annealing under low heating rates and slow cooling resulted in both BCC α-FeNi and FCC γ-FeNi nanocrystallites with an average grain size on the order of 25-27 nm whereas high heating rates achieved via flash annealing techniques have enabled a dramatically refined microstructure consisting of 5-7 nm grains with FCC γ-FeNi phase and found to be the dominant phase following primary crystallization. Grain size refinement and phase identity optimization yielded low values of coercivities-17 A/m and high permeability similar to 11 x 10 3 measured at 400 Hz/1 kA/m in flash annealed samples at 450 °C for 5 s. The magnetic behavior and the underlying mechanism of optimal soft magnetic properties are discussed in terms of the critical role of the grain size in domain wall pinning and coercivity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Grain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction

Nanostructuring, structure distortion and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg 0.97 Sb 0.99 , with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. In this work, we report the average grain size of 24-28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron X-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg 0.97 Sb 0.99 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Evolution of the superconducting properties from binary to ternary APC-Nb 3 Sn wires

We present a study conducted on binary Tube Type and ternary powder-in-tube Nb 3 Sn wires manufactured using the artificial pinning centres-internal oxidation method. All the specimens are doped with Zr: oxide nano-particles of this element are responsible for the pinning improvement, both by refining the A-15 grain-size and their own point-pinning contribution. Low-field J c magnetometry confirms that the hadron-hadron Future Circular Collider (FCC-hh) specifications are met by one ternary doped-sample. The differences in microstructure were assessed by scanning electron microscopy/transmission electron microscopy to clarify the reasons for the pinning improvement between the two generations. The deviations from the Dew Hughes model are also discussed, underlying some non-linear addition due to competition between the two pinning mechanisms. Finally, we show how the introduction of Ta as a ternary addition influences the A-15 phase by focusing on the radial inhomogeneities, evaluating the T c distribution and Sn composition gradients. The latter are used to model the currents, enabling us to evaluate the individual weights of the pinning mechanisms and their absolute contributions at the High Luminosity-Large Hadron Collider and FCC-hh dipoles operational points.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Friction-based riveting technique for AZ31 magnesium alloy

Rivet materials used in the aerospace and automotive industries are typically alloys of aluminum (Al) or steel. Magnesium (Mg) is an attractive alternative because it is 33% and 75% lighter than Al and steel, respectively. However, a primary barrier for using Mg as rivet material is its poor formability at room temperature, resulting in brittle fracture of the rivet head during cold riveting. Hot riveting is possible but suffers from high cycle time due to the need for pre-heating. A new friction-based riveting technique, Rotating Hammer Riveting (RHR), is reported to fully form AZ31 Mg rivet heads in a mere 0.23 seconds cycle time. Heat and pressure generated through severe plastic deformation during the process was sufficient to form the Mg rivet head without the need for a separate pre-heating operation. Due to dynamic recrystallization, AZ31 Mg grains in the rivet head were significantly refined from about 15 to 2.6 µm during RHR, which favors the formability of Mg rivet by triggering grain boundary sliding and reducing plastic anisotropy of Mg. In addition, RHR joints showed a metallurgical bond between the rivet head and top sheet, which eliminates a significant pathway for corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Statistical fracture behavior of doped UO 2 using a ball-on-ring equibiaxial flexure test method

Metal oxide dopants, such as titanium and chromium oxides, have garnered considerable attention for their potential to increase grain size (≥ 30 µm) in UO 2 fuel, purportedly enhancing fission gas retention during reactor operation. Fuel performance is significantly impacted by fuel fracture behavior, so it is important to understand the effects of enhanced grain size and dopant content on UO 2 fuel fracture. UO 2 pellets were doped with 0.1 wt% TiO 2 and 0.3 wt% Cr 2 O 3 to alter density and grain size. Inductively coupled plasma mass spectroscopy measured dopant levels pre- and post-sintering. X-ray diffraction revealed lattice changes and microstrain via Rietveld refinement. Field emission scanning electron microscopy determined grain sizes of approximately 30 µm for TiO 2 doping and 7 µm for Cr 2 O 3 doping. Transverse rupture strength tests were performed on over 30 samples per dataset to obtain characteristic strength and Weibull modulus. Results indicate no statistical difference in fracture strength between 0.1 wt% TiO 2 doped UO 2 and undoped UO 2 , while 0.3 wt% Cr 2 O 3 doped UO 2 exhibited a 20% decrease in fracture strength. Doped UO 2 samples also showed reduced Weibull modulus compared to undoped UO 2 , suggesting increased scatter in fracture strength. This study's findings suggest that titanium and chromium oxide doping in UO 2 , regardless of grain size, induce residual stresses, decreasing fracture strength and increasing variability in fracture behavior.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Quantum Fast Approximate Synthesis Tool (QFAST) v1.0.0

We present QFAST, a quantum synthesis tool designed to produce short circuits and to scale well in practice. Our contributions are: 1) a novel representation of circuits able to encode placement and topology; 2) a hierarchical approach with an iterative refinement formulation that combines "coarse-grained" fast optimization during circuit structure search with a good, but slower, optimization stage only in the final circuit instantiation stage. When compared against state-of-the-art techniques, although not optimal, QFAST can generate much shorter circuits for "time dependent evolution" algorithms used by domain scientists. We also show the composability and tunability of our formulation in terms of circuit depth and running time. For example, we show how to generate shorter circuits by plugging in the best available third party synthesis algorithm at a given hierarchy level. Composability enables portability across chip architectures, which is missing from the available approaches.

Younis, Ed↗
DOE OSTI2021

Microstructure and Mechanical Properties of the AA7075 Tube Fabricated using Shear Assisted Processing and Extrusion (ShAPE)

Shear Assisted Processing and Extrusion (ShAPE) experimental setup and tooling were adopted for extruding thin-walled AA7075 aluminum tube from as-cast non-homogenized billet material in a single run. The mechanical and microstructural characterizations were performed on the extrudate in the as-extruded condition without subsequent heat treating. It was shown that the ShAPE process developed a significantly refined microstructure with uniform and almost equiaxed grain structure on both hoop and axial cross-sections of the extrudate as well as through the thickness of the material. The pole figures and inverse pole figures of the EBSD data showed an strong shear texture development, and it was found out that axial shear is the dominant deformation mechanism in the regions near the inner surface of the tube, while combined axial and torsional shears are the two dominant modes of deformation near the outer surface of the extrudate. As for the mechanical properties, there was an increase of 150% and 73% in the yield and ultimate strengths of the tube produced using ShAPE process, respectively, and a 18% decrease in maximum uniform plastic elongation compared to the conventionally extruded AA7075-O tube.

Shear Assisted Processing and Extrusion, Friction ↗
DOE OSTI2022

Friction extrusion of ODS copper rod made from powder

Meters-long oxide dispersion strengthened copper rods were manufactured directly from powder by a single-step process, called friction extrusion. The average grain size was 880 nm, which was refined 40 times from powder precursor due to extensive shear deformation. Meanwhile, the average size of alumina particles was 60 nm which retains a decent oxide dispersion strengthening. Here, mechanical properties, including hardness, tensile strength, and ductility, were tested and found to have better or similar values than conventional sintered-then-extruded oxide dispersion strengthened copper materials. The presented technique promises a convenient avenue for the fabrication of oxide dispersion strengthened copper from powder.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Process Intensification for Nanostructure Aluminum Extrusions

A new technology called Shear Assisted Processing and Extrusion (ShAPE™), pioneered at the Pacific Northwest National Laboratory (PNNL), has the potential to revolutionize the US extrusion industry. Maturation of the ShAPE™ process would create a new cross cutting US manufacturing technology that advances three key the objectives within AMO; namely, nanomaterials processing, process intensification, and materials for extreme and harsh environments. PNNL and SCM Metals Products, Inc. (SCM), a division of Kymera International, will collaborate to mature the ShAPE™ extrusion process beyond TRL 3 to increase the likelihood of its adoption by industry. PNNL’s custom (one-of-a-kind in the world) ShAPE™ machine will be used to extrude round rods of high strength aluminum alloy feedstock powder provided by SCM. As proof-of-concept, PNNL has previously extruded 5 mm diameter rods with SCM aluminum alloy powder AL-12.4TM. This project aims to scale up the process to a diameter of 25 mm while retaining the excellent mechanical properties achieved for the 5 mm diameter rods. The degree of process intensification with ShAPE™ will also be estimated. The primary objectives of this project are as follows. 1) Fabricate 25 mm diameter nanostructured extrusions in bulk, directly from AL-12.4TM aluminum alloy powder without the need for canning, degassing, compaction, and other intermediate steps typical of powder metallurgy extrusion. 2) Achieve a microstructure with an ultrafine grained (UFG <1 µm) aluminum matrix having refined and homogenously distributed nanoscale second phases. 3) Show that the ram force can be significantly reduced compared to conventional powder metallurgy extrusion of the same material and estimate the extent of process intensification that may be possible with ShAPE™. 4) Demonstrate improved high-temperature mechanical properties compared to conventional extrusion of the same material. The following tasks will be undertaken to achieve these objectives. PNNL will develop the die set and process parameters necessary to fabricate Al-12.4TM extrusions with a 25 mm diameter. Microstructural analysis will be performed by PNNL while mechanical testing will be conducted by SCM. With information learned from the process development and characterization, PNNL will perform an estimate of the degree of process intensification that may be possible with ShAPE™.

42 ENGINEERING↗