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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Experimental studies on metallic fuel relocation in a pin bundle core structure of a sodium-cooled fast reactor

Understanding the relocation behavior of metallic fuel in severe accident scenarios is one of the most important factors in the safety assessment of sodium-cooled fast reactors (SFRs). In the present study, the relocation behavior of uranium metallic fuel was investigated by conducting metallic fuel relocation experiments using 19-pin bundle test sections in the Argonne's Metallic Uranium Safety Experiment (MUSE) facility. Post-test radiographic images were taken to characterize the uranium fuel relocation within the pin bundle test section. In addition, the pressure drop in the test sections was measured after the relocation experiments to evaluate the blockage of the sodium coolant channel. The pressure drop in the pin bundle test sections was also analytically calculated by varying the porosity and the pore size of the relocated fuel. The porosity and pore size of the relocated fuel in the pin bundle test sections were estimated by comparing those calculated pressure drop values with the measured pressure drop values from the pressure drop tests. In this work, the experimental results showed that the more formation of the eutectics could lead to more fuel dispersion and less blockage due to the lower freezing point of the eutectics.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2020

Effect of ATF Cr-coated-Zircaloy on BWR In-vessel Accident Progression during a Station Blackout

The deposition of protective coatings on nuclear fuel cladding has been considered as a near-term Accident Tolerant Fuel (ATF) concept that will reduce the high-temperature oxidation rate and enhance accident tolerance of the cladding while providing additional benefits during normal and transient. In this study, the performance of the proposed ATF concept of Cr-coated-Zircaloy is assessed using a generic Boiling Water Reactor MELCOR plant model considering a Short-term Station Blackout (STSBO) scenario. Simulation results indicate that the use of Cr-coated-Zircaloy as cladding and canister material mitigates the core degradation process as compared to the traditional Zircaloy cladding and canister design. The onset of fuel degradation and collapse is delayed by over thirty minutes, and the extent of fuel degradation is reduced. Specifically, the gross in-vessel hydrogen generation decreased by almost a factor of three. Although the eutectic reaction between Cr-coating and Zircaloy could cause an early failure of the coating, the improvement in the delay of fuel degradation is still notable. In addition, a thicker coating is found helpful to obtain additional coping time and to decrease hydrogen generation. In addition to the eutectic formation that may compromise Cr-coated Zr, a different failure mode is identified for the Cr-coated-Zr when compared to Zircaloy; i.e., a complete melt of base material leads to component collapse before the coating is oxidized and consumed. These findings can help the industry focus on productive areas of research and development for accident-tolerant fuel concepts and enhancement of core safety margins.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Solvation Dynamics of Wet Ethaline: Water is the Magic Component

The past two decades witnessed the development of a new type of solvent system, named deep eutectic solvents, which have become increasingly investigated because they offer new and potentially favorable properties, such as wide tunability in electrochemical, mechanical, and transport properties. Deep eutectic solvent (DES) systems are composed of at least one main solvent and an additional component that is meant to interrupt the original solvent/solvent interactions, thereby introducing lower melting points relative to each individual component. Ethaline (a 1:2 mole% mixture of choline chloride and ethylene glycol) is one of the most promising DES systems. However, it is also known to be very hygroscopic, which is a constant concern because water absorption during the use of ethaline alters its properties. Within this work, we demonstrate that modest amounts of water addition (1-10%) to ethaline are of little concern for practical use and can even lead to performance improvements, such as accelerated relaxation and solvation. In contrast, very small amounts of <1% of water lead to additional slowing of the solvent response. Thus, we suggest that the attempt to dry ethaline below 1% moisture is rather counter-productive if one attempts to achieve effective solvation and charge transport properties from DESs. This study investigates the effect of water content on the diffusional relaxation dynamics of ethaline. A set of independent spectroscopic experiments and computational simulations are aimed to provide insight into the solvent response of the DES system using femtosecond time-resolved absorption spectroscopy (fs-TA), broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR) diffusometry and broadband relaxometry, and molecular dynamics simulations (MDS) on ethaline with 0, 0.1, 1, 10, and 28.5wt% added water. For dry ethaline, we identify choline chloride as the rate-limiting solvation component in ethaline. However, the role of the solvent components changes gradually as water is added. Further, we provide quantitative solvent relaxation rates using the different presented time-resolved spectroscopic techniques and find remarkable agreement between them. Based on the solvent relaxation rates and combined with MDS, we develop a molecular understanding of the individual solvent components and their interactions in dry and wet ethaline with varying amounts of water content.

25 ENERGY STORAGE↗
DOE OSTI2015

Scalable Synthesis of Defect Abundant Si Nanorods for High-Performance Li-Ion Battery Anodes

Microsized nanostructured silicon–carbon composite is a promising anode material for high energy Li-ion batteries. However, large-scale synthesis of high-performance nano-Si materials at a low cost still remains a significant challenge. Here we report a scalable low cost method to synthesize Al/Na-doped and defect-abundant Si nanorods that have excellent electrochemical performance with high first-cycle Coulombic efficiency (90%). The unique Si nanorods are synthesized by acid etching the refined and rapidly solidified eutectic Al–Si ingot. To maintain the high electronic conductivity, a thin layer of carbon is then coated on the Si nanorods by carbonization of self-polymerized polydopamine (PDA) at 800 °C. The carbon coated Si nanorods (Si@C) electrode at 0.9 mg cm –2 loading (corresponding to area-specific-capacity of ~2.0 mAh cm –2 ) exhibits a reversible capacity of ~2200 mAh g –1 at 100 mA g –1 current, and maintains ~700 mAh g –1 over 1000 cycles at 1000 mA g –1 with a capacity decay rate of 0.02% per cycle. High Coulombic efficiencies of 87% in the first cycle and ~99.7% after 5 cycles are achieved due to the formation of an artificial Al 2 O 3 solid electrolyte interphase (SEI) on the Si surface, and the low surface area (31 m 2 g –1 ), which has never been reported before for nano-Si anodes. The excellent electrochemical performance results from the massive defects (twins, stacking faults, dislocations) and Al/Na doping in Si nanorods induced by rapid solidification and Na salt modifications; this greatly enhances the robustness of Si from the volume changes and alleviates the mechanical stress/strain of the Si nanorods during the lithium insertion/extraction process. Introducing massive defects and Al/Na doping in eutectic Si nanorods for Li-ion battery anodes is unexplored territory. We venture this uncharted territory to commercialize this nanostructured Si anode for the next generation of Li-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2015

Near-isothermal furnace for in situ and real time X-ray radiography solidification experiments

In this paper, we present a newly developed near-isothermal X-ray transparent furnace for in situ imaging of solidification processes in thin metallic samples. We show that the furnace is ideally suited to study equiaxed microstructure evolution and grain interaction. To observe the growth dynamics of equiaxed dendritic structures, a minimal temperature gradient across the sample is required. A uniform thermal profile inside a circular sample is achieved by positioning the sample in the center of a cylindrical furnace body surrounded by a circular heater arrangement. Performance tests with the hypo-eutectic Al-15wt.%Cu and the near-eutectic Al-33wt.%Cu alloys validate the near-isothermal character of the sample environment. Controlled cooling rates of less than 0.5 K min{sup −1} up to 10 K min{sup −1} can be achieved in a temperature range of 720 K–1220 K. Integrated in our rotatable laboratory X-ray facility, X-RISE, the furnace provides a large field of view of 10.5 mm in diameter and a high spatial resolution of ∼4 μm. With the here presented furnace, equiaxed dendrite growth models can be rigorously tested against experiments on metal alloys by, e.g., enabling dendrite growth velocities to be determined as a function of undercooling or solutal fields in front of the growing dendrite to be measured.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synergistic stabilization of metastable Fe{sub 23}B{sub 6} and γ-Fe in undercooled Fe{sub 83}B{sub 17}

Previous investigations of undercooled liquid Fe{sub 83}B{sub 17} near the eutectic composition have found that metastable crystalline phases, such as Fe{sub 23}B{sub 6}, can be formed and persist down to ambient temperature even for rather modest cooling rates. Using time-resolved high-energy x-ray diffraction on electrostatically levitated samples of Fe{sub 83}B{sub 17}, we demonstrate that the Fe{sub 23}B{sub 6} metastable phase and fcc γ-Fe grow coherently from the undercooled Fe{sub 83}B{sub 17} liquid and effectively suppress the formation of the equilibrium Fe{sub 2}B + bcc α-Fe phases. The stabilization of γ-Fe offers another opportunity for experimental investigations of magnetism in metastable fcc iron.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Maxwell–Stefan diffusion and dynamical correlation in molten LiF-KF: A molecular dynamics study

In this work our main objective is to compute Dynamical correlations, Onsager coefficients and Maxwell-Stefan (MS) diffusivities for molten salt LiF-KF mixture at various thermodynamic states through Green–Kubo formalism for the first time. The equilibrium molecular dynamics (MD) simulations were performed using BHM potential for LiF–KF mixture. The velocity autocorrelations functions involving Li ions reflect the endurance of cage dynamics or backscattering with temperature. The magnitude of Onsager coefficients for all pairs increases with increase in temperature. Interestingly most of the Onsager coefficients has almost maximum magnitude at the eutectic composition indicating the most dynamic character of the eutectic mixture. MS diffusivity hence diffusion for all ion pairs increases in the system with increasing temperature. Smooth variation of the diffusivity values denies any network formation in the mixture. Also, the striking feature is the noticeable concentration dependence of MS diffusivity between cation-cation pair, Đ{sub Li-K} which remains negative for most of the concentration range but changes sign to become positive for higher LiF concentration. The negative MS diffusivity is acceptable as it satisfies the non-negative entropy constraint governed by 2{sup nd} law of thermodynamics. This high diffusivity also vouches the candidature of molten salt as a coolant.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Safeguards in Pyroprocessing: an Integrated Model Development and Measurement Data Analysis

Pyroprocessing is an electrochemical method based on the molten salt electrolyte, mainly the LiCl-KCl eutectic molten salt, to recycle the used nuclear fuel. For a conceptual design of commercial pyroprocessing facility, tons of special nuclear materials, namely U and Pu, may be involved, which could be used for non-peaceful purposes if they are diverted. Effective safeguards approaches have to be developed prior to the development and construction of a pyroprocessing facility. Present research focused on two main objectives, namely calculating the properties of nuclear species in LiCl-KCl molten salt and developing integrated model to safeguard a pyroprocessing facility. Understanding the characteristics of special nuclear materials in LiCl-KCl eutectic salt is extremely important to understand their behaviors in an electrorefiner. The model development for the separation processes in the pyroprocessing, including electrorefining, actinide drawdown, and rare earth drawdown benefits the understanding of material transport and separation performance of these processes under various conditions. The output signals, such as potential, current, and species concentration contribute to the material balance closure and provide safeguards signatures to detect the scenarios of diversion. U and Pu are the two main elements concerned in this study due to our interest in safeguards.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Electrolytes in Multiple-Phase Hydrogen Storage Reactions

Multiple-phase hydrogen storage materials such as metal alanates and borohydrides, and destabilized systems offer the possibility of high hydrogen storage capacity with favorable thermodynamics. However, the multiphase nature of these materials intrinsically limits the kinetics due to the required transport of species between phases, which are typically in dry powder form. To address this limitation, the influence of added electrolytes is explored. This approach is motivated by analogy with similar multiphase battery reactions that show reduced kinetic limitations while necessarily containing electrolytes. Previous experimental results showing improved kinetics for MgH2/Sn (using a LiBH4/KBH4 eutectic electrolyte) and NaAlH4 (using a diglyme electrolyte) are further analyzed in terms of this analogy. The results show that the analogy is useful and rate constants are increased. Importantly, the inclusion of an electrolyte also appears to alleviate the continuously decreasing rates with the extent of reaction, which is characteristic of many multiphase hydrides. Instead, reaction rates are approximately constant until near completion. Together, these effects can lead to >10× shorter overall reaction times. In addition, new results are presented for the hydrogenation of MgB2 using Li/K/CsI and Li/K/CsCl eutectic electrolytes, where >60% conversion to Mg(BH4)2 was demonstrated at 350 bar.

08 HYDROGEN↗
DOE OSTI2016

Thermodynamic Assessment of LiCl-KCl-PuCl{sub 3} Ternary System

Pyroprocessing in LiCl-KCl molten salt is being considered as an alternative to the PUREX for the used nuclear fuel treatment. As more and more spent fuel is reprocessed, the composition of molten salt electrolyte changes, which alters the thermodynamic properties of the system and subsequently requires the adjustment of operation conditions. In order to optimize the system design and carefully operate it, thermodynamic assessment of actinides and lanthanides in LiCl-KCl molten salt is needed. Even though several systems have been assessed recently, such as LiCl-KCl-CeCl{sub 3} and LiCl-KCl-UCl{sub 3}, as one of the major actinides in pyro-processing, PuCl{sub 3} in LiCl-KCl hasn't been calculated. In present work, LiCl- KCl-PuCl{sub 3} is being considered and studied. Sub-binary systems of LiCl-PuCl{sub 3} and LiCl-KCl system was calculated firstly by using two-sublattice model based on the CALPHAD (Calculation of Phase Diagram) theory. The result indicates both of LiCl-PuCl{sub 3} and LiCl-KCl show simple eutectic properties and no solid solution is found. This research will help to predict the properties in electro-refiner when the concentration of elements in LiCl- KCl molten salt electrolyte changes during pyro-processing. Currently, binary system of KCl-PuCl{sub 3} is also being assessed and after that, phase diagram of ternary system of LiCl-KCl-PuCl{sub 3} will be calculated to provide a whole sight of the properties of PuCl{sub 3} in LiCl-KCl eutectic salt. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Fundamental Study of Uranium Dendrites Electrochemically Separated in Molten Salt with the Presence of Cerium

In this study, uranium was electrochemically separated in the presence of cerium in eutectic LiCl-KCl at varying concentrations of cerium and varying overpotentials. Harvested dendrites were then examined and analyzed for their morphological features and elemental composition using various analytical techniques. Conclusions: Increasing the applied overpotential causes the dendrites to evolve from relatively simple and large platelet-like crystals (25 mV), to a grid-like network with crystals having jagged and smooth features (50 mV, 100 mV), and finally into a very chaotic and complex crystal morphology (200 mV) for all uranium-cerium compositions explored. Varying the uranium:cerium concentration ratio did not have much effect on the uranium dendrite morphologies. EDS results show that cerium is not co-deposited on the surface of the dendrite crystals, ICP-MS results do show a presence of cerium in the volumetric composition. This is likely due to salt occlusion during the dendrite formation. XRD has been performed on several samples at the 25 mV overpotential with 1 wt% U and 0 wt% Ce in the molten salt eutectic. These results indicate that there is not salt occlusion within the dendrites during electrochemical separation. Additionally, the uranium metal quickly oxidizes during preparation for XRD.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Electrochemical and Thermodynamic Properties of U in LiCl-KCl-UCl{sub 3} salt system

Pyro-processing technology has been considered and examined by several countries as a promising method for the recovery and recycle of uranium and actinide elements from used nuclear fuel. One of the key processes in pyro-processing is an electro-refiner (ER) where the metallic fission products are loaded into an anode basket and dissolved into lithium-potassium chloride (LiCl-KCl) eutectic salt at 773 K. Many researchers have been exploring the fundamental characterizations of U in LiCl-KCl system by using various electrochemical methods, resulting in several reported values of diffusion coefficient, apparent standard potential, and activity coefficient of U in the salt system. In addition, several researchers measured kinetic parameter of U (exchange current density, i{sub 0}) by using Tafel and linear polarization (LP) methods. Despite available data sets on this ternary salt system, there are discrepancies due to different experimental conditions, design, size of the cell, and measurement techniques. In addition, the i{sub 0} for U/U{sup 3+} reaction has only been measured since 2009; therefore, only few data sets are available to date although the i{sub 0} is critical for the development of dynamic ER model. The value of i{sub 0} is a kinetic characteristic in an ideal equilibrium state; therefore, it is very challenging to be measured by experiments. The authors have estimated the values of i{sub 0} via Tafel and linear polarization methods (LP); however, these methods are lack of maintaining electrode surface area during the measurements. In addition, some data are not following the trends from other literature studies due to its difficulties of the measurement. Therefore, further experimental determinations have to be accomplished to understand the i{sub 0} kinetics and the database for the i{sub 0} of U/U{sup 3+} couple in LiCl-KCl eutectic salt needs to be established systematically. In the present study, an experimental setup was designed and used in a consistent manner to build a meaningful database for U in LiCl-KCl system. LiCl-KCl-UCl{sub 3} salt was prepared at different concentrations and temperatures ranging from 0.5 wt% to 4 wt% and 723 K to 798 K, respectively. Then, CV, open circuit potential (OCP), and electrochemical impedance spectroscopy (EIS) were performed to understand the electrochemical, thermodynamic, and kinetic properties of U. Specially, i{sub 0} values have not been measured via EIS method; therefore, this study provides a good chance to confirm the i{sub 0} values with the new technique.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Enhanced Tensile and Tear Toughness Properties of Thin-Wall Vacuum-Assisted High-Pressure Die-Cast Aural-5 Alloy by Friction Stir Processing

Steadily rising demand for glider weight reduction has driven the development of vacuum-assisted high-pressure die-cast (HPDC) Al-alloys for automotive structural components. Aural-5 is a strontium-modified HPDC alloy utilizing manganese (Mn) to reduce die soldering, eliminating detrimental needle-shaped Fe-bearing ß-phase intermetallic and improving ductility. HPDC Aural-5 contains shrinkage porosity, dendrites with Al-Si eutectic colonies, externally solidified crystals (ESCs), shear-band structure, and large second-phase particulates. Porosity, ESCs and large second-phase particles work as crack initiation sites, negatively impacting tensile properties. In this study, friction stir processing (FSP) is employed for microstructural modification of a thin-walled HPDC Aural-5 by eliminating porosity and breaking down dendrites, second-phase particles, eutectic colonies, ESCs and shear-band structures to create wrought microstructure with homogenized particle distribution. Mechanical property characterization indicates ~30% and ~35% enhancement in yield strength and ductility and associated marked effects on ~69% improvement in tear toughness according to the ASTM B871 test.

Friction stir processing, Aural-5, Strength, Tear ↗
DOE OSTI2024

Design and Characterization of Hierarchically-Strengthened, Cast Al-Ce-Ni-Mn-Sc-Zr Alloys for High-Temperature Applications

We characterize the microstructure and mechanical properties of cast Al-Ce-Ni-Mn-Sc-Zr alloys designed for structural use above 300 °C. We first report on the effect of Ni on the as-cast phase formation, where all alloys consist of fine Al11Ce3 and Ni-rich eutectic phases, but the identity of the Ni-rich phase varies with Ni content. Furthermore, these alloys contain four coarsening-resistant strengthening phases as determined from SEM and APT investigations: (i) Al11Ce3 and (ii) Ni-rich micron-scale platelets formed during eutectic solidification, (iii) L12-Al3(Sc,Zr) nanoprecipitates formed during secondary aging, and (iv) Mn solute in the α-Al matrix. The Al-Ce-Ni-Mn-Sc-Zr alloy possesses higher microhardness and creep resistance than compositionally simpler alloys containing fewer of the strengthening phases, indicating that these strengthening mechanisms synergize to provide increased ambient- and elevated-temperature strength.

Ekaputra, Clement↗
DOE OSTI2017

Synthesis, Spectral Characterization, Thermal and Optical Studies of Novel Complexes: 4-(Dimethylamino)benzylidene-4-acetamideaniline and 4-(Dimethylamino)benzylidene-4-nitroaniline

The phase diagram representing solid–liquid equilibrium of entire range of composition and thermodynamic studies of two binary organic systems of 4-dimethylaminobenzaldehyde (DMAB) with two NLO active compounds, p-aminoacetanilide (PAA) and p-nitroaniline (PNA), have been studied by solid state synthetic route. Both systems are independently forming a new entity called intermolecular complex (IMC) and two eutectics on either side of intermolecular complexes. The various thermodynamic parameters such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions of IMCs and eutectics were calculated using the heat of fusion values. The TGA and DTA studies were performed to understand the physico-chemical, thermal behavior and unique identity of newly synthesized organic complexes, 4-(dimethylamino)benzylidene-4-acetamideaniline (DMABPAA) and 4-(dimethylamino)benzylidene-4-nitroaniline (DMABPNA), and their respective enthalpy of fusion values were found to be 30.01 and 37.26 kJ mol{sup − 1}. The higher melting point of both the novel complexes than their parent’s compounds reveal the strong molecular interaction between parent components to yield the complex. The FTIR spectral analysis predicts the disappearance of aldehyde peaks of DMAB and NH{sub 2} peaks of PAA and PNA while the appearance of entirely new peaks than that of parent’s compounds are the supportive for the formation of new molecular entities. These findings are further supported by FTNMR spectrum studies by observation of disappearance of proton peak of aldehyde of DMAB and amine peaks of PAA and PNA rather formation of new imine proton peak or peaks were observed. The appearance of new peaks in Powder XRD of complexes than those of parent components is further indicative for the formation of complexes. The absorption spectrum of DMABPAA and DMABPNA showed intra-molecular charge-transfer (ICT) excited state absorption at 258 and 241 nm, respectively. Both the IMCs, DMABPAA and DMABPNA, show strong fluorescence with quantum yield 0.66 and 0.93, respectively, in methanol solution.

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

Dechlorination of molten chloride waste salt from electrorefining via ion-exchange using pelletized ultra-stable H-Y zeolite in a fluidized particle reactor

Dechlorination of eutectic LiCl–KCl based electrorefner (ER) salt is reported via ion-exchange reaction with protonated ultrastable Y-type (USHY) zeolite bound into mechanically fuidized 45–250 μm diameter particles. Evidence of exchange of cations from the salt (Li + , K + , and fission product cations) into the zeolite lattice replacing H + ions was found based on a change in unit cell size, ICP-MS, XRD and TEM–EDS in addition to detection of HCl of gas. Ion exchange reaction was carried out at 625 and 650 °C, temperatures above the melting point of eutectic LiCl–KCl. Experiments were carried out to optimize zeolite drying temperature, estimate maximum ion-exchange capacity, and determine the thermal stability of USHY zeolite. The results indicate over 90% dechlorination can be achieved without zeolite structure collapse at 625 °C. Finally, this provides a promising route to stabilizing waste from radioactive chloride salts into dechlorinated waste forms for permanent geologic disposal.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

The Effects of Silicon and Niobium Concentration on the Solidification Behavior and Microstructure of Cast Monel Alloys

Cast Monel alloys are used in applications requiring a combination of good mechanical properties and excellent resistance to corrosion. Despite prevalent industrial use, relatively few studies have been conducted to investigate the relationships between composition, solidification behavior, and microstructure. Given that these alloys are used in the cast and welded conditions, these factors have a significant influence over the material properties. Here, in this work, microstructural characterization, electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry were used to study how changes in Si and Nb concentrations affected the solidification path and microstructure of Monel alloys. It was found that increasing Nb concentration stabilized higher amounts of MC carbides and suppressed graphite formation during solidification. It was also found that the high nominal concentration and segregation of Si to the liquid led to the formation of Ni 31 Si 12 and other silicides via terminal eutectic reactions at the end of solidification. A pseudo-binary solidification diagram was constructed using experimental data and was applied to predict the mass fraction of solidified eutectic as a function of composition. The modeled microstructures were found to be in good agreement with experimentally measured phase fractions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

In-Situ Synchrotron X-Ray Diffraction of Ultrasonic Microstructural Refinement During Solidification in a Commercial Al–Si–Mg Alloy

This study reports the first use of in-situ synchrotron X-ray diffraction (SXRD) to study the effects of ultrasonic melt processing (USMP) on phase and grain size evolution during solidification in a commercial Al–Si–Mg casting alloy. USMP is a technique that, when applied to aluminum as it solidifies, can be used to refine the local microstructure of large-scale castings. Analysis of the in-situ SXRD data to estimate the average grain size of primary α-Al grains during USMP demonstrates that USMP slows the growth rate of α-Al grains and reduces grain size by 36 pct. Furthermore, there is also evidence that USMP causes the primary α-Al grains to move relative to the X-ray beam; such motion increases the probability of primary α-Al grains colliding and fragmenting. This movement becomes constrained at the onset of the Al–Si binary eutectic, suggesting that USMP ceases to effectively refine the microstructure once the Al–Si binary eutectic begins to form. Complementary laboratory-scale X-ray diffraction (XRD) data were used to correlate the lattice parameters of the α-Al and Si (D-A4) phases with temperature to estimate cooling rate during solidification. Thus, this study can guide the design of novel castings with spatially distributed fine-grained regions produced using local ultrasonic processing.

Aluminum Alloys↗