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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 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 OSTI2023

Microstructural refinement in ultrasonically modified A356 aluminum castings

Two A356 aluminum alloys (Al-Si-Mg), one with 0.09 wt.% Fe and one with 0.91 wt.% Fe, were cast in a graphite mold with the simultaneous application of local ultrasonic intensification to refine the as-cast microstructure. Ultrasonication during casting transformed the morphology of primary Al grains from dendritic (~140-290 microns in size) to globular (~33-36 microns in size). The alloy with high Fe exhibited globular grains at distances up to 45 mm away from the ultrasound probe, while the alloy with low Fe exhibited globular grains at distances only up to 6 mm away from the ultrasound probe. Near the location of the ultrasound probe (< 2 mm away), a second non-dendritic microstructural morphology was observed with fine aluminum grains (~9-25 microns in size). This unique fine-grained morphology has not been previously reported, contains a greater concentration of Si relative to the globular microstructure, and may be a large, fully eutectic region. Ultrasonication during casting also transformed the morphology of the ß-Al 5 FeSi phase particles (which are deleterious to the strength and ductility of the alloy) in the high Fe alloy from needle-like to rectangular, which could enable the greater use of secondary Al alloys. Thermodynamic simulations conducted to calculate the solidification paths of the two alloys studied predict that the ß-Al 5 FeSi phase begins to form earlier in the alloy with high Fe. Finally, data suggest that the ß-Al 5 FeSi phase (which is more abundant in alloys with high Fe content) may enhance ultrasonically-induced grain refinement.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Refining Microstructures in Additively Manufactured Al/Cu Gradients Through TiB 2 Inclusions

Here, the additive manufacture of compositionally graded Al/Cu parts by laser engineered net shaping (LENS) is demonstrated. The use of a blue light build laser enabled deposition on a Cu substrate. The thermal gradient and rapid solidification inherent to selective laser melting enabled mass transport of Cu up to 4 mm from a Cu substrate through a pure Al deposition, providing a means of producing gradients with finer step sizes than the printed layer thicknesses. Divorcing gradient continuity from layer or particle size makes LENS a potentially enabling technology for the manufacture of graded density impactors for ramp compression experiments. Printing graded structures with pure Al, however, was prevented by the growth of Al 2 Cu 3 dendrites and acicular grains amid a matrix of Al 2 Cu. A combination of adding TiB 2 grain refining powder and actively varying print layer composition suppressed the dendritic growth mode and produced an equiaxed microstructure in a compositionally graded part. Material phase was characterized for crystal structure and nanoindentation hardness to enable a discussion of phase evolution in the rapidly solidifying melt pool of a LENS print.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Microstructural Development in Inconel 718 Nickel-Based Superalloy Additively Manufactured by Laser Powder Bed Fusion

Excellent weldability and high temperature stability make Inconel 718 (IN718) one of the most popular alloys to be produced by additive manufacturing. Here in this study, we investigated the effects of laser powder bed fusion (LPBF) parameters on the microstructure and relative density of IN718. The samples were fabricated with independently varied laser power (125 - 350W), laser scan speed (200 - 2200 mm/s), and laser scan rotation (0° - 90°). Archimedes’ method, optical microscopy, and scanning electron microscopy were employed to assess the influence of LPBF parameters on the relative density and microstructure. Optimal processing windows were identified for a wide range of processing parameters and relative density greater than 99.5% was achieved using volumetric energy density between 50 and 100 J/mm3. Microstructural features including melt pool geometry, lack of fusion defect, keyhole porosity, and sub-grain cellular microstructure were examined and quantified to correlate to LPBF parameters. A simple empirical model was postulated to relate relative sample density and LPBF volumetric energy density. Melt pool dimensions were quantitatively measured and compared to estimations based on Rosenthal solution, which yielded a good agreement with the width, but underestimated the depth, particularly at high energy input, due to lack of consideration for keyhole mode. In addition, the sub-grain cellular-dendritic microstructure in the as-built samples was observed to decrease with increasing laser scan speed. Quantification of the sub-micron cellular-dendritic microstructure yielded estimated cooling rate in the order of 10 5 – 10 7 K/s.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Interface velocity dependent solute trapping and phase selection during rapid solidification of laser melted hypo-eutectic Al-11at.%Cu alloy

Microstructure formation of a hypo-eutectic Al-11Cu (atom percent) alloy during solidification after laser melting has been studied by transmission electron microscopy (TEM). The evolution of the solid-liquid-interface velocity, V SL , during the solidification process has been determined from direct observation by in-situ TEM. This enabled correlating V SL with development of four distinct microstructure zones. Crystal growth mode transitions from planar to cellular, cellular to dendritic, dendritic to cellular, and cellular to planar, have been observed for the accelerating solid-liquid-interface. The transition from coupled two-phase growth to the single-phase growth occurred for V SL = V a = (0.80±0.05) m/s, where V a is the velocity of absolute stability, at the onset of banded morphology grain formation. The in-situ and post-mortem TEM uniquely permitted determination of the non-equilibrium solidus for the rapidly solidifying Al-11Cu alloy. Experimental evidence for solute clustering and chemical ordering tendencies at length scales on the order of ≤ 5nm has been detected in the single-phase regions of the banded grains. The structural features of the single-phase bands have been interpreted as signatures of ‘frozen in’ configurations present in the liquid boundary layer adjacent to the growing crystal, which has a width of about 3nm. Finally, the nano-scale spatiotemporal resolution experimental TEM studies performed here provided quantitative metrics, e.g. the solidification interface velocity dependent solute concentration of the α-Al phase and the near-atomic scale structure in the single-phase bands, that are uniquely suitable for comparison with theory and model predictions for solidification microstructure development in multicomponent alloys after laser melting.

36 MATERIALS SCIENCE↗
DOE OSTI2020

In situ and ex situ studies of anomalous eutectic formation in undercooled Ni–Sn alloys

Anomalous eutectic formation in undercooled Ni-Sn alloys was investigated by in situ X-ray diffraction and ex situ remelting and annealing experiments. Dynamic recrystallization and partial remelting of primary solids followed by repeated nucleation and growth of eutectic grains in the mushy zone were revealed by time-resolved X-ray diffraction. Ex situ experiments demonstrated that partial remelting of near-equilibrium solidified alloys of eutectic or near-eutectic composition can convert regular lamellar eutectic into anomalous eutectic, whereas high-temperature annealing of splat-quenched alloys of similar composition can convert eutectic or two-phase dendrites into anomalous eutectic. It is concluded that compared to ripening in solid-states, partial remelting of eutectic or two-phase dendrites in a mushy zone provides a more realistic mechanism for anomalous eutectic formation in undercooled solidification of Ni-Sn eutectic alloys. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Crystal growth↗
DOE OSTI2024

Understanding the influence of boron in additively manufactured GammaPrint®-700 CoNi-based superalloy

Boron is commonly added to superalloys in small amounts to enhance creep resistance, but can lead to cracking at high concentrations, especially during the additive manufacturing process. Two variants of CoNi-based GammaPrint®-700 superalloy with different B contents (0.08 at% vs 0.16 at%) were printed via laser powder bed fusion (LPBF) with the same printing parameters, with only the high B alloy exhibiting solidification cracking. Atom probe tomography (APT) revealed stronger segregation behaviors in the high B alloy compared to the low B alloy at both the inter-dendritic regions and grain boundaries (GBs). The segregation behavior at inter-dendritic regions was well captured with Scheil simulation and can correlate with the existing cracking susceptibility index (CSI) on cracking tendencies, although high angle GBs are where cracking occurs according to electron backscatter diffraction (EBSD) measurements. Additionally, the extent of GB segregation was compared between the high B and low B alloy. Higher B additions led to significantly more GB B segregation in the high B alloy compared to the low B alloy. Further, for the high B alloy, the cracked region of one GB exhibited higher levels of B compared to the uncracked region of the same GB. However, much higher B contents were also found in two other uncracked GBs in the high B alloy, which demonstrates that higher GB B concentrations are not fully responsible for the cracking. A much larger variance in GB B segregation content was found in the high B alloy compared to the low B alloy. These phenomena were explained with a solidification model with the GB segregation content expressed explicitly by a modified Langmuir-McLean equation. This model linked the GB segregation content with solidification undercooling, which can be used as quantitative cracking criteria for future builds.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A redox-active organic cation for safer metallic lithium-based batteries

Safety concerns have severely impeded the practical application of high-energy-density lithium-based batteries. Dendrite growth and overcharging can lead to particularly catastrophic thermal failure. Here we report an organic cation, trisaminocyclopropenium (TAC), as a bi-functional electrolyte additive to suppress dendrite growth and offer reversible overcharge protection for metallic lithium-based batteries. During the Li plating process, TAC cations with aliphatic chains can form a positively charged electrostatic shield around Li protrusions, repelling the approaching Li + and thereby attaining a more uniform plating. A two times longer cycle life of 300 h at 1 mA cm -2 is achieved in a Li|Li symmetric cell in comparison with the control. During the overcharging process, the redox-active TAC can repeatedly shuttle between two electrodes, maintaining the cell voltage within a safe value. A solid protection of 117 cycles (~1640 h) at 0.2 C with a 100% overcharge is achieved in a LiFePO 4 /Li 4 Ti 5 O 12 cell. This study sheds fresh light on the ability of organic cations to build safer batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Thermal stability and coarsening of eutectic and near-eutectic Ni–Ce alloys

Ni–Ce alloys are currently being studied as a castable alternative to conventional Ni-based superalloys. To understand the evolution of microstructure and mechanical behavior at elevated temperatures, this study investigates the mechanism of coarsening behavior in eutectic and near eutectic Ni–Ce at 900 °C. The as-cast eutectic Ni–Ce consists of a combination of fine lamellar and rod eutectic colonies with coarser boundary regions. Upon annealing, continuous coarsening, via process of globularization, initiates at colony boundaries or primary dendrites where faults (termination and branches) in the lamellar structure are plentiful. Coarsening then proceeds by a combination of fault migration mechanism and lamellar boundary splitting, growing toward the center of the eutectic colonies with increasing annealing time. Coarsening near the center of a colony is extremely slow, indicating the eutectic microstructure itself is very stable. Here, the near-eutectic alloys containing primary dendrites coarsen and stabilize faster compared to the fully eutectic alloy. Moreover, an anomaly is observed in the hardness of the fully eutectic alloy after long exposure at elevated temperature compared to the near-eutectic alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Morphological and Phenotypic Characteristics of the Bovine Nasopharyngeal Mucosa and Associated Lymphoid Tissue

The mammalian nasopharynx is an anatomically complex region of the upper respiratory tract that directly communicates with the nasal cavity, laryngopharynx, oesophagus and trachea. The nasopharyngeal mucosa contains moderate quantities of mucosa-associated lymphoid tissue (MALT) that is appropriately located for immunological sampling but also creates vulnerability to pathogens. In recent years, the nasopharynx has been inculpated in the pathogenesis of important diseases of cattle (foot-and-mouth disease) and humans (COVID-19), yet the tissue has never been described in detail in any species. In order to characterize the morphology and cellular composition of the bovine nasopharynx, samples of mucosa were collected from the nasopharynx of five 8–13-month-old steers and examined using light microscopy, immunohistochemistry and multichannel immunofluorescence. Morphologically, the nasopharyngeal epithelium was highly heterogeneous, with a continuum ranging from stratified squamous epithelium to highly attenuated, follicle-associated epithelium (FAE). Distribution of MALT was similarly regionally variable ranging from absent to clusters of multiple lymphoid follicles. Phenotypic characterization demonstrated dense distributions of dendritic cells and T lymphocytes surrounding lymphoid follicles, which comprised mostly B lymphocytes. The FAE overlaying the lymphoid follicles also contained higher numbers of dendritic cells and lymphocytes compared with the adjacent non-lymphoid epithelium, although cytotoxic T cells were notably scarce in the FAE. The bovine nasopharyngeal lymphoid tissue had comparable elements to other MALTs with specific differences that may help to elucidate the pathogenesis of infectious agents that have specific tropism for this tissue.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Lithiophilic CoF 2 @C hollow spheres towards spatial lithium deposition for stable lithium metal batteries

Lithium metal (LM) is a promising anode for next-generation batteries due to its high theoretical capacity and low electrode potential. Nonetheless, side reactions, volume change, and unwanted lithium dendrite growth seriously limit the practical application of LM. Herein, with the aid of a hard template approach, a novel lithiophilic CoF 2 -carbon hollow sphere (CoF 2 @C-HS) composite material is successfully prepared via a facile in-situ fluorination and etching strategy. The lithiophilic CoF 2 acts as nucleation sites to reduce nucleation overpotential as well as induces the spatial Li deposition and the formation of LiF-rich solid electrolyte interphase (SEI), and the hollow carbon matrix can enhance the electrical conductivity and offer free space for LM deposition. Theoretical simulations reveal that the synergistic effect of lithiophilic CoF 2 and hollow carbon matrix homogenizes the electric field distribution and Li + flux. Benefiting from these advantages, the CoF 2 @C-HS-modified copper substrate electrode delivers an enhanced Coulombic efficiency (CE) of 93.7% for 280 cycles at 1 mA cm –2 and 1 mA h cm –2 . The symmetrical cell using CoF 2 @C-HS can stably cycle more than 1800 h with a low voltage hysteresis of 11 mV at a current density of 0.5 mA cm –2 and an areal capacity of 0.5 mA h cm –2 . Moreover, the Li@CoF 2 @C-HS composite anode enables more than 300 stable cycles at 1 C with a capacity retention of 95% in LiFePO 4 -based full cell and 110 stable cycles at 1 C in LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)-based high-voltage full cell. Finally, this work might shed a new light on designing lithiophilic hosts to spatially confine LM deposition, realizing dendrite-free LM anodes and the practical applications of LM batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Microstructure-refinement–driven enhanced tensile properties of high-pressure die-cast A380 alloy through friction stir processing

This work employs friction stir processing (FSP), a well-known severe plastic deformation technique, to selectively modify the microstructure of thin-walled, high-pressure die-cast (HPDC) aluminum alloy A380, a major HPDC alloy fabricated in the die casting sector. FSP effectively breaks down Al dendrites and acicular Si particles, creating a homogenized distribution of equiaxed Si particles in the aluminum matrix. After FSP, the refined Si particles (~1.5 µm) are smaller than the eutectic Si particles (3–8 µm) in HPDC condition. In addition, interparticle distance has decreased almost 50% compared to dendritic arm spacing, and FSP has reduced the aspect ratio of Si particles to ~2. Furthermore, FSP eliminates porosity, and breaks down needle-like second-phase Fe-Mn and Cu-rich particles, yielding a refined, homogeneous distribution. The FSP-induced microstructural refinement and porosity reduction improve bulk yield strength and ductility by 23% and 66%. Tensile properties are enhanced beyond those of the die skin of the HPDC plate, and the alloy possesses lower defect density and a highly refined microstructure. This study establishes the viability of FSP as a tool for microstructure modification and mechanical property improvement for HPDC Al alloys for the light-weighting goal of the automotive industries.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dehalogenation of electrochemical processing salt simulants with ammonium phosphates and immobilization of salt cations in an iron phosphate glass waste form

This study demonstrates the conversion of simulated pyroprocessing salt wastes [i.e., ER(SF) and ERV2] into chemically durable iron phosphate glass waste forms through reactions with ammonium hydrogen phosphate precursors [i.e., NH4H2PO4 and (NH4)2HPO4] and added Fe2O3. The reaction of the salt simulants with the phosphate precursors resulted in dehalogenation of the salt through the production of NH4Cl and NH4I (along with water), of which the NH4Cl can be used to produce UCl3 oxidant for use in the electrorefiner during pyroprocessing. These iron phosphate glasses contain a notably higher waste loading than the baseline glass-bonded sodalite ceramic waste form, which requires about 70 vol% sodalite to accommodate Cl from the salt, because they are dehalogenated prior to vitrification. The high waste loadings coupled with higher bulk densities (~3×103 kg/m3) than glass-bonded sodalite (~2.3×103 kg/m3) mean that these glasses have a higher storage volume, i.e., the volume required to immobilize a given mass of waste. The iron phosphate glass waste forms were characterized using a variety of techniques including physical property measurements and chemical durability testing. Following initial testing, a proof-of-concept demonstration was conducted to show that the NH4Cl generated from this process could be used to produce UCl3 using depleted uranium dendrites as a feedstock.

phosphate glass, pyroprocessing, waste forms, salt↗
DOE OSTI2020

Effect of binder on the overcharge response in LiFePO 4 -containing cells

Two types of small pouch cells based on LiFePO 4 /graphite, one containing a N-methyl pyrrolidinone (NMP)-soluble binder, poly(vinylidene difluoride), and the other an aqueous-soluble binder, styrene-butadiene rubber/carboxymethylcellulose were systematically charged to 100, 120, 140, 160, 180, and 250% state of charge (SOC). The cells were then discharged to 3.0 V at room temperature before being disassembled for postmortem analysis. Microstructural changes in the anode associated with increasing SOC were more pronounced in the aqueous processed cells in comparison to the NMP-processed cells. Dendrite formation was observed on the aqueous-processed anode at 120% SOC, while the NMP-processed anode surface does not show dendrites until 250% SOC. Overall, the aqueous-processed anode surfaces displayed more evidence of microstructural degradation as a function of increasing SOC. In the NMP-processed cells, four organic compounds on the anode surface were found to show a dependence on SOC, while only two displayed a similar dependency in the aqueous-processed cells. The nature of the binder changed the number and composition of the species found at the anode.

25 ENERGY STORAGE↗
DOE OSTI2020

Towards a high-performance garnet-based solid-state Li metal battery: A perspective on recent advances

Garnet-based solid-state Li metal batteries have been widely considered one of the most promising next-generation energy storage systems. However, the performance of these batteries is plagued by various limitations caused by the solid-state electrolyte (SSE). The poor wetting of lithium on the garnet surface diminishes the contact between the anode and electrolyte, leading to extremely high anode interfacial resistance. Similarly, the point-to-point contact between the cathode and electrolyte leads to high impedance on the cathode side. Moreover, although the SSE serves a firm barrier separating the anode and cathode, lithium dendrites can still grow through, causing a short circuit. Lastly, the solid/solid interface cannot be well maintained under cycling at high current density and capacity. Recently, remarkable progress has been achieved in garnet electrolyte to resolve these problems towards the aim of a high-performance solid-state Li metal battery. In this perspective, we highlight various recent advances in the field of garnet-based solid-state battery, including improving the anode/electrolyte interface, lithium dendrite detection, reducing cathode impedance, and electrolyte architecture design.

25 ENERGY STORAGE↗
DOE OSTI2025

Mapping of fracture and ionic conductivity changes in ion implanted solid electrolytes: Insights from molecular dynamics

Ion implantation emerges as a promising technique to address the persistent challenge of lithium (Li) filament growth in solid-state electrolytes as it can induce compressive stresses inhibiting crack growth and deflect dendrites, de facto mitigating early electrolyte failure. In this study, we examine the potential paradox of ion implantation: while aiming to enhance electrolyte performance, the radiation damage associated with implantation might inadvertently compromise both the ionic conductivity and the intrinsic fracture toughness of the material, rendering the material unsuitable for battery applications. Specifically, we employed molecular dynamics simulations to examine the scope of the downsides of ion implantation, specifically: (i) reduced ionic conductivity (due to radiation-induced amorphization) and (ii) mechanical stability (due to radiation-induced embrittlement) in ion-implanted Li 7 La 3 Zr 2 O 12 (LLZO) solid-state electrolytes. We explore how radiation damage impacts LLZO’s crystalline structure, Li-ion diffusion, and fracture properties at various temperatures and radiation damage levels. The study aims to provide insights into the competing effects of ion implantation and suggest potential engineering strategies for developing more robust solid-state electrolytes with improved conductivity and dendrite resistance.

Conductivity↗
DOE OSTI2022

Closed-loop control of meltpool temperature in directed energy deposition

The objective of this work is to mitigate flaw formation in powder and laser-based directed energy deposition (DED) additive manufacturing process through close-loop control of the meltpool temperature. In this work, the meltpool temperature was controlled by modulating the laser power based on feedback signals from a coaxial two-wavelength imaging pyrometer. The utility of closed-loop control in DED is demonstrated in the context of practically inspired trapezoid-shaped stainlesssteel parts (SS 316L). We demonstrate that parts built under closed-loop control have reduced variation in porosity and uniform microstructure compared to parts built under open-loop conditions. For example, post-process characterization showed that closed-loop processed parts had a volume percent porosity ranging from 0.036% to 0.043%. In comparison, open-loop processed parts had a larger variation in volume percent porosity ranging from 0.032% to 0.068%. Further, parts built with closed-loop processing depicted consistent dendritic microstructure. By contrast, parts built with open-loop processing showed microstructure heterogeneity with the presence of both dendritic and planar grains, which in turn translated to large variation in microhardness

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multimodal and multiscale strengthening mechanisms in Al-Ni-Zr-Ti-Mn alloy processed by laser powder bed fusion additive manufacturing

The unique thermokinetics of laser-powder bed fusion additive manufacturing (L-PBFAM) has been exploited for development of a novel high-strength Al-Ni-Ti-Zr-Mn alloy. The addition of 0.5 wt% Mn leads to extraordinary improvement in ultimate tensile strength (502 MPa) and work hardening due to the activation of two Mn-induced strengthening mechanisms. First, by a bimodal particle strengthening effect due to Al 31 Mn 6 Ni 12 nano-quasi-crystal particles rejected in inter-dendritic spaces and fibrous Al 3 Ni eutectic dendritic channels, which predominately contributes to the strength improvement, and second by solid solution strengthening from remaining Mn entrapped in Al. These mechanisms supplement the particle strengthening effect imparted by coherent and incoherent Al 3 (Ti,Zr) co-precipitates present at melt pool boundaries, dislocation strengthening due to solidification induced strain, and Hall-Petch and backstress strengthening effect due to heterogenous grain size distribution occurring at various length scales. In conclusion, the solidification dynamics and hierarchical heat distribution that are associated with L-PBFAM resulted in complex spatial variations in these strengthening phenomena and were investigated via a high-throughput multiscale structure–property correlation that involved thermokinetic simulation, X-ray diffraction, high-resolution nanoindentation mapping, and site-specific transmission electron microscopy of the alloy.

36 MATERIALS SCIENCE↗