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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Upcycling of aluminum Twitch scrap via Shear Assisted Processing and Extrusion (ShAPE)

Aluminum is publicly perceived as recyclable, but mixed alloys and impurities in aluminum scrap require dilution via energy-intensive primary aluminum or downcycling to low-quality castings. In this study, cast billets of shredded aluminum scrap (Twitch) were blended with pre-consumer AA 6061, extruded into tubes via Shear Assisted Processing and Extrusion (ShAPE), and aged to T1 and T6 tempers. Microscopy reveals that ShAPE refined and distributed the deleterious AlFeSi phases. Furthermore, the Twitch extrusions had tensile properties comparable to AA 6061 yet without homogenizing or adding primary aluminum. Energy savings were 85% compared to conventional extrusion of primary aluminum alloys.

ShAPE↗
DOE OSTI2015

Effect of cold rolling on the microstructure and mechanical properties of Al 0.25 CoCrFe 1.25 Ni 1.25 high-entropy alloy

Cold rolling can break down the as-cast dendrite microstructure and thus may have pronounced impact on the mechanical behavior of the alloy. In the present study, the effect of cold rolling on the microstructure and mechanical properties of Al 0.25 CoCrFe 1.25 Ni 1.25 high-entropy alloy in the face-centered cubic structure was investigated. With increasing the thickness reduction from cold rolling, the hardness, the yield strength, and the fracture strength increased at the cost of reducing ductility. At the thickness reduction of 80%, the tensile strength (hardness) was 702 MPa (406 MPa), 1.62 (2.43) times that in the as-cast condition. Compared to traditional alloys, Al 0.25 CoCrFe 1.25 Ni 1.25 has the highest hardening rate with respect to CR thickness reduction. Lastly, the phase relation and the mixing properties of Gibbs free energy, enthalpy and entropy of Al x CoCrFe 1.25 Ni 1.25 were predicted using the CALPHAD method.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magnesium Alloy ZK60 Tubing made by Shear Assisted Processing and Extrusion (ShAPE)

ZK60 Magnesium tubing has been friction extruded from as-cast billets and T5 conditioned bars using Shear Assisted Processing and Extrusion (ShAPE). Tubes having an outer diameter of 50.8 mm and wall thickness of 1.9 mm were extruded with >20 times less ram force compared to conventional extrusion due to the unique shearing conditions and tooling inherent to ShAPE. Microstructures of the as-cast billet and T5 bar feedstock materials were significantly different from each other in terms of grain size, texture, and second phase distribution; yet the resulting microstructures after ShAPE were remarkably similar. An average grain size of 4-5 microns, 20o tilt of basal texture away from the extrusion axis, and refined second phases having a uniform distribution were achieved independent of the feedstock material. Hardness for as-extruded and artificially aged tubes are presented with isotropic behavior explained by detailed microstructural analysis. This work suggests that bulk ZK60 magnesium alloys extrusions may be fabricated in a single step, with microstructures that are unobtainable with conventional extrusion.

Friction Stir Extrusion, Friction Consolidation an↗
DOE OSTI2020

Relationship between ductility and the porosity of additively manufactured AlSi10Mg

Additive manufacturing via selective laser melting can result in variable levels of internal porosity both between build plates and within components from the same build. In this work, sample porosity levels were compared to tensile properties for 176 samples spanning eight different build plates. Sample porosity was measured both by Archimedes density, which provided an estimation of overall porosity, and by observation of voids in the fracture surface, which provided an estimation of the porosity at the failure plane. The porosity observed at the fracture surface consistently demonstrated higher porosity than that suggested by Archimedes density. The porosity values obtained from both methods were compared against the mechanical results. Sample porosity appears to have some correlation to the ultimate tensile strength, yield strength, and modulus, but the strongest relationship is observed between porosity and ductility. Three different models were used to relate the fracture surface porosity to the ductility. The first method was a simple linear regression analysis, while the other two models have been used to relate porosity to ductility in cast alloys. It is shown that all three models fit the data well over the observed porosity ranges, suggesting that the models taken from casting theory can extend to additively manufactured metals. Finally, it is proposed that the non-destructive Archimedes method could be used to estimate an approximate sample ductility through the use of correlations realized here. Such a relationship could prove useful for design and for a deeper understanding of the impact of pores on tensile behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Co-, Ni- and Fe-rich grain-boundary phases enhance creep resistance in θ'-strengthened Al-Cu alloys

Here, microstructural evolution and creep response were investigated in the cast Al-5.0Cu-0.3Mn-0.2Zr (wt.%) alloy with and without addition of slow-diffusing, intermetallic-forming elements Fe, Ni, or Co. Baseline Al-5.0Cu-0.3Mn-0.2Zr alloy exhibits high creep resistance at 300 °C, up to ~75 MPa, which is attributed to high-aspect-ratio, intragranular θ'-Al 2 Cu precipitates that effectively suppress dislocation climb. However, θ'-Al 2 Cu precipitate-free zones form along grain boundaries upon heat treatment, whose extent is amplified during subsequent creep. Such weak regions experience dislocation creep, leading to strain localization and acceleration of grain-boundary sliding. Adding Ni and Co, individually or in combination, leads to the formation of grain-boundary precipitates (Al 9 Co 2 , Al 3 Ni 2 ) which are resistant to coarsening, thus suppressing the formation of θ'-Al 2 Cu precipitate-free zones. This microstructure provides high creep resistance at stresses up to 75–80 MPa, with strain rates much lower than in unmodified Al-5.0Cu-0.3Mn-0.2Zr. Adding Fe, which results in extensive decoration of grain boundaries with coarsening-resistant Al 7 Cu 2 Fe, and then increasing the Cu content to compensate for the Cu loss to this new phase, leads to a new Al-7.4Cu-1.6Fe-0.3Mn-0.2Zr alloy with creep resistance at 300 °C that surpasses known cast aluminum alloys. Adding Fe to improve the creep resistance of Al-Cu alloys is both cost-effective and sustainable. Our findings offer guidelines applicable to various alloy systems on controlling the evolution of precipitate-free zones and its ensuing effects on creep deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Microstructural refinement of an Al-Ce-Mg alloy via Shear Assisted Processing and Extrusion

Al-Ce alloys have attracted recent interest because of their high thermal stability due to the low solubility of Ce in the Al matrix. The Al 11 Ce 3 eutectic phase gives excellent strain hardening behavior and moderate high-temperature strength in the as-cast state. However, its strengthening effect is limited by its coarse as-cast structure. Therefore, alternative manufacturing methods such as additive manufacturing or equal channel angular pressing have been applied to refine the Al 11 Ce 3 phase to good effect. However, these techniques are both expensive and time-consuming. Therefore, this study aims to use Shear Assisted Processing and Extrusion (ShAPE), an emerging solid phase processing technique that is more easily scalable than the previously mentioned methods. ShAPE can produce useful cross-sections of an Al-8Ce-4Mg alloy while refining the Al 11 Ce 3 phase to produce a higher strength material. It was found that a low temperature ShAPE process can improve the room temperature yield strength by ~60 % compared to a binary Al-4Mg alloy. Additionally, the high-temperature yield strength of the Al-Ce alloys increased by 20%, with a simultaneous 15% improvement in ductility compared to the binary Al-Mg alloy. Finally, these results highlight the potential for ShAPE as a processing technique for Al-Ce alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of the as-built microstructure on the recrystallization of an additively manufactured Inconel939 Ni-based superalloy

This study investigates the influence of the as-built microstructure on the recrystallization (RX) behavior and mechanical properties of the Ni-based superalloy Inconel 939 produced by laser powder bed fusion (PBF-LB/M). Two distinct as-built microstructures were obtained by varying the hatch distance (h d ): a columnar, strongly textured condition (h d =50, termed h d 50) and an equiaxed, weakly textured condition (h d =70, termed h d 70)). Both were subjected to nine solution treatments combining three temperatures (1100, 1150, and 1200 °C) and three holding times (1, 4, and 8 h). Comprehensive microstructural characterization was conducted to assess grain morphology, texture, grain boundary character, dislocation density, and precipitate distribution. Recrystallization was found to be significantly slower than in cast counterparts, requiring higher temperatures and longer times for completion. The initial microstructure plays a decisive role: full RX was achieved only in hd70 specimens after treatment at 1200 °C for 8 h, whereas hd50 samples exhibited delayed and incomplete RX under identical conditions. This behavior is attributed to the finer grain size and higher fraction of high-angle grain boundaries in hd70, which promote recrystallization. Mechanical testing revealed that hd70 samples subjected to a 1200 °C/8 h treatment followed by standard double ageing show higher yield and tensile strengths across the investigated temperature range than both printed and cast Inconel939 processed under conventional conditions, albeit with slightly reduced ductility. The enhanced mechanical performance is attributed to the larger grain size, which limits grain boundary sliding. These results demonstrate the critical importance of controlling the as-built microstructure and tailoring post-processing strategies to optimize high-temperature performance of PBF-LB/M Inconel939.

Inconel939↗
DOE OSTI2022

Minimizing thickness variation in monolithic U-10Mo fuel foil and Zr interlayer during hot rolling: A microstructure-based finite element method analysis

Low-enriched uranium alloyed with 10 wt. % molybdenum (U-10Mo) has been identified as a promising alternative to highly enriched uranium fuel for the United States’ high performance research reactors. The monolithic U-10Mo fuel plate consists of a metallic U-10Mo fuel foil with a 25 µm Zr interlayer and a relatively thick cladding of aluminum alloy 6061. The Zr interlayer is typically applied during the hot co-rolling process, and this process dictates the uniformity of the Zr interlayer. Thickness variation observed in the U-10Mo and Zr interlayer has been attributed to several sources: the initial grain size of the U-10Mo castings, can materials, rolling temperature, inhomogeneous molybdenum content, and porosity in the cast U-10Mo. This thickness variation limits the ability to meet the dimensional specification; thus, a better understanding of the factors causing the nonuniform thickness is needed. In this work, we used a novel, microstructure-based finite element method to model the hot rolling process to address these concerns. Grain microstructures in U-10Mo were tessellated and explicitly considered in the finite element model. Each grain was assigned a random material property to mimic the grain strength variations induced by different grain orientations. Simulations were performed using six steel can thicknesses, four grain sizes, and with or without a Zr interlayer to investigate the influences of those variables on the thickness nonuniformity. The simulation results showed that a thinner steel can and finer U-10Mo grain size reduce thickness variations in both the U-10Mo fuel foil and Zr interlayer. The direct findings from the simulations and analysis can be used to optimize the hot rolling schedule, reduce fabrication defects, and meet the dimensional specifications. The proposed microstructure-based finite element model can be also coupled with experimental microstructure characterization data, images, and models to simulate multi-pass hot rolling.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Novel use of a hand-held laser induced breakdown spectroscopy instrument to monitor hydride corrosion in uranium

With a compact hand-held laser-induced breakdown spectroscopy (LIBS) instrument, studies were performed on specimens of uranium charged with controlled hydrogen concentrations for a qualitative evaluation of hydride corrosion. Four samples of depleted uranium with two different starting microstructures (cast and rolled) were used for this study. The hydrogen charged samples (rolled 1.8 wppm H and cast 14 wppm H by weight) are representative of the pre-corrosion states with hydrides distributed throughout the bulk. In-depth LIBS measurements were carried out, after the thick surface corrosion layer was removed, by applying 100 laser pulses from sample surface into the bulk on five different sample locations. Three additional areas on each sample were investigated by laser ablation using a 12-point grid approach. The atomic emission signals of elemental uranium, carbon, hydrogen, and oxygen were identified and analyzed. All four samples showed similar uranium and carbon concentrations, as expected. Hydrogen content was consistent with each sample's specification, such that the hydrogen charged samples exhibited higher hydrogen concentration than their references. Both specimens charged with hydrogen showed elevated oxygen content as well, due to rapid oxidation of uranium and uranium hydrides. The oxidation process was facilitated by the laser ablation and plasma plume's high temperature effects on the sample combined with the glovebox environment. The uranium surface damage produced by laser ablation was quantitatively evaluated by optical microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Endogeic earthworm densities increase in response to higher fine-root production in a forest exposed to elevated CO 2

Net primary productivity (NPP) influences soil food webs and ultimately the amount of carbon (C) inputs in ecosystems. Earthworms can physically protect organic matter from rapid mineralization through the formation of soil aggregates. Previous studies at the Oak Ridge National Laboratory (ORNL) Free Air CO 2 Enrichment (FACE) experiment showed that elevated [CO 2 ] (e[CO 2 ]) increased fine-root production and increased soil C through soil aggregation compared to ambient [CO 2 ] (a[CO 2 ]) conditions. Our first objective was to study the response of earthworms to increased leaf and root-litter inputs caused by increased atmospheric [CO 2 ] exposure. Here, we also took advantage of the CO 2 shutdown at the ORNL FACE site to track the shift of the δ 13 C signal in leaf-litter, fine roots, earthworms, earthworm casts, and bulk soil. Densities of the most abundant endogeic earthworm, Diplocardia spp., were positively correlated with the previous-year production of leaf litter (r=0.66, P=0.02) and fine roots (r=0.62, P=0.03); and with the leaf-litter production (r=0.63, P=0.03) and fine-root production (r=0.59, P=0.05) two years before earthworms were sampled. Within two years after the CO 2 fumigation ceased, the 13 C/ 12 C ratio increased in leaf litter (P=0.01) and in fine roots (P=0.05), showing an ecosystem legacy effect on soil C inputs. However, the C isotopic composition of soil, endogeic earthworms and casts had not changed the two years after the CO 2 fumigation ended. The positive response of earthworms to increased root NPP, caused by elevated [CO 2 ], is consistent with the increased soil aggregate formation and increased soil C at the ORNL FACE in the e[CO 2 ] treatment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Gas expanded polymer process to anneal nanoparticle dispersion in thin films

A spin-coating solution comprising poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) nanoparticles used to create organic photovoltaic (OPV) active layers have been shown to adopt a non-uniform concentration profile across the thin film dimension. This inhomogeneous distribution can reduce the efficiency of the device. For our new process, gas expanded polymer (GXP) annealing, is applied to P3HT/PCBM thin film blends, enabling the distribution of the PCBM nanoparticles to be manipulated by varying the GXP processing conditions. Films of 50 nm thickness (nominally) created by spin casting a blend of P3HT mixed with PCBM were annealed by oscillatory GXP and GXP at constant pressure using high pressure CO 2 . An increase in P3HT crystallinity (detected by X-ray diffraction and UV-vis spectroscopy) along with a more uniform distribution of PCBM nanoparticles in the thickness dimension, as interpreted from neutron reflectivity measurements, were observed after oscillatory GXP annealing. In addition, static water contact angles suggest that the film/air interface is enriched in PCBM relative to the as-cast film. Finally, these results demonstrate that GXP annealing, which is commercially scalable, can be successfully used to create a uniform distribution of PCBM nanoparticles across the thickness dimension in a P3HT thin film.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A Markov framework for generalized post-event systems recovery modeling: From single to multihazards

State-dependent models can be used to represent the system recovery process as a series of stochastic transitions from lower to higher functional states. However, the applications of these models have been limited in scope and there is a lack of a generalized recovery modeling framework. A generalized framework would permit a robust forecasting of systems and system-of-systems recovery under multiple hazards, and more broadly, would contribute to community disaster preparedness. This paper develops a generalized post hazard-event recovery modeling framework based on state-dependent Markov-type processes. We then apply the proposed framework to solve a spectrum of problems that range from hind-casting single-system recovery following a single hazard event to forecasting post-event trajectories under multiple hazards and modeling the recovery of a system-of-systems. First, Markov chains are used to hind-cast the observed recovery for a portfolio of buildings affected by the 2014 South Napa, California, earthquake. Next, Markov processes are used to formulate a parametric post hazard-event recovery model, which can be updated using Bayesian statistics when relevant datasets become available. Semi-Markov processes are then used to develop a more general model of single hazard recovery, which accounts for the intensity of the loading and level of damage caused by the event. Semi-Markov processes with non-renewal features are then used to account for multihazard interactions in a post-event recovery model, and applied to a case study that involves a community in Charleston, South Carolina. Lastly, Markov-type processes are combined with Bayesian networks to model the recovery of residential, commercial, educational, and industrial buildings (system-of-systems) following a hazard event. Overall, these applications demonstrate the versatility of the Markov framework towards handling recovery problems with varying levels of complexity.

42 ENGINEERING↗
DOE OSTI2016

Application of the Uranium–Helium Chronometer to the Analysis of Nuclear Forensic Materials

Radiochronometers are used to constrain the manufacturing and processing history of actinide materials for nuclear forensic investigations. This paper describes here U–He ages and He diffusion kinetics obtained from a metallic, highly enriched uranium sample. The average U–He age is 8% older than the known casting date, which indicates that excess He is present and is likely due to incomplete degassing of pre-existing He during the casting process. Although the U–He age is older than expected, the accuracy is comparable to other chronometers that have been applied to this material. Diffusion kinetics obtained from the uranium metal indicate that He is quantitatively retained under plausible storage conditions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Growth-Controlled Broad Emission in Phase-Pure Two-Dimensional Hybrid Perovskite Films

Two-dimensional hybrid metal halide perovskites (2D perovskites) are attractive for light-emitting devices and other applications because their emission is tunable across the visible spectrum. The emission profile of 2D perovskites can be broadened via a variety of mechanisms and is further complicated by the presence of impurities. Here, the challenge of making phase-pure films in Ruddlesden–Popper phases [(A') 2 (A) n–1 B n X 3n+1 structure] is overcome by using a single A/A'-site cation, ethylammonium (EA), whose optimal size also prohibits the formation of off-target phases. In the (EA) 2 (EA) n–1 Pb n Br 3n+1 family, the low-energy, broad emission observed in bulk crystals is reduced in spin-cast, polycrystalline films. This decrease in broad emission, attributed to phonon-mediated processes, is correlated with the strain in polycrystalline films that is observed by X-ray scattering. Photothermal deflection spectroscopy shows that strain also increases the electronic disorder near the free exciton absorbance. Broad emission in films can be recovered by slowing growth kinetics, which removes the strain acquired from spin-casting and increases the domain size. Furthermore, these results help extend the utility of 2D perovskites by suggesting design rules for the growth of thin films with the targeted phase and emission.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Low-Vapor-Pressure Solvent Additives Function as Polymer Swelling Agents in Bulk Heterojunction Organic Photovoltaics

Here, bulk heterojunction (BHJ) photovoltaics based on blends of conjugated polymers and fullerenes require an optimized nanoscale morphology. Casting BHJ films using solvent additives such as 1,8-diiodooctane (DIO), 1,8-octanedithiol (ODT), chloronapthalene (CN), or diphenyl ether (DPE) often helps achieve this proper morphology: adding just a few volume percent of additive to the casting solution can improve polymer/fullerene mixing or phase separation, so that solvent additives have become staples in producing high-efficiency BHJ solar cells. The mechanism by which these additives improve BHJ morphology, however, is poorly understood. Here, we investigate how these additives control polymer/fullerene mixing by taking advantage of sequential processing (SqP), in which the polymer is deposited first and then the fullerene is intercalated into the polymer underlayer in a second processing step using a quasi-orthogonal solvent. In this way, SqP isolates the role of the additives’ interactions with the polymer and the fullerene.

1,8-diiodooctane↗
DOE OSTI2016

A Solvent-Vapor Approach toward the Control of Block Ionomer Morphologies

Sulfonated block ionomers possess advantageous properties for a wide range of diverse applications such as desalination membranes, fuel cells, electroactive media, and photovoltaic devices. Unfortunately, their inherently high incompatibilities and glass transition temperatures e ff ectively prevent the use of thermal annealing, routinely employed to re fi ne the morphologies of nonionic block copolymers. An alternative approach is therefore required to promote morphological equilibration in block ionomers. The present study explores the morphological characteristics of midblock- sulfonated pentablock ionomers (SBIs) di ff ering in their degree of sulfonation (DOS) and cast from solution followed by solvent-vapor annealing (SVA). Transmission electron microscopy con fi rms that fi lms deposited from di ff erent solvent systems form nonequilibrium morphologies due to solvent-regulated self-assembly and drying. A series of SVA tests performed with solvents varying in polarity reveals that exposing cast fi lms to tetrahydrofuran (THF) vapor for at least 2 h constitutes the most e ff ective SVA protocol, yielding the anticipated equilibrium morphology. That is, three SBI grades subjected to THF-SVA self-assemble into well-ordered lamellae wherein the increase in DOS is accompanied by an increase in lamellar periodicity, as measured by small-angle X-ray scattering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Nonaggregating Doped Polymers Based on Poly(3,4-Propylenedioxythiophene)

Electrical doping of organic semiconductors is critical for their use in electrical devices. However, many high-performance semiconductors exhibit drastically reduced solubilities when doped in solution, making it difficult to deconvolute the roles of doping and morphological changes on their electrical properties. We report the synthesis of a semiconducting polymer based on poly(3,4-propylenedioxythiophene) (ProDOT) substituted with oligo(ethylene glycol) (EG) side chains that is designed to solvate dopant molecules. When doped with F 4 TCNQ in solution, the polymer P(ProDOT-EG) undergoes efficient charge transfer while remaining soluble with no indication of aggregation. The electrical conductivity of thin films cast from heavily doped solutions is ~1 S/cm; optical spectroscopy reveals that the doping efficiency is reduced upon formation of the solid film. Diffusion of F 4 TCNQ from the vapor phase into films of neutral P(ProDOT-EG) yields comparable conductivities to films cast from doped solutions. Absorption spectroscopy and X-ray diffraction of doped films reveal that the doping efficiency and nature of charge carriers (polaron or bipolaron) are strongly affected by the processing route. The lack of the localized polaron signature for films doped by infiltration of the dopant from the vapor phase indicates that morphology has a large role in determining the nature of the charge carriers in semiconducting polymers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Robust Chiral Organization of Cellulose Nanocrystals in Capillary Confinement

Here we showed large area uniformly aligned chiral photonic bioderived films from a liquid crystal phase formed by a cellulose nanocrystal (CNC) suspension placed in a thin capillary. As a result of the spatial confinement of the drying process, the interface between coexisting isotropic and chiral phases aligns perpendicular to the long axis of the capillary. This orientation facilitates a fast homogeneous growth of chiral pseudolayers parallel to the interface. Overall, the formation of organized solids takes hours vs weeks in contrast to the slow and heterogeneous process of drying from the traditional dish-cast approach. The saturation of water vapor in one end of the capillary causes anisotropic drying and promotes unidirectional propagation of the anisotropic phase in large regions that results in chiral CNC solid films with a uniformly oriented layered morphology. Corresponding ordering processes were monitored in situ at a nanoscale, mesoscale, and microscopic scale with complementary scattering and microscopic techniques. The resulting films show high orientation order at a multilength scale over large regions and preserved chiral handedness causing a narrower optical reflectance band and uniform birefringence over macroscopic regions in contrast to traditional dish-cast CNC films and those assembled in a magnetic field and on porous substrates. Finally, these thin films with a controllable and well-identified uniform morphology, structural colors, and handedness open up interesting possibilities for broad applications in bioderived photonic nanomaterials.

36 MATERIALS SCIENCE↗