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At least 397 records · Page 22

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DOE OSTI2025

Overcoming the Damping–Elasticity Paradox via 3D‐Printed NiTiSn Nanocomposite

Abstract Developing high damping alloys (HDAs) with large elastic strain has attracted growing attention due to the increasing demand for energy absorption with overload reliability and reusability. However, damping capacity inherently conflicts with elasticity, because the former requires a liable movement of crystal defects while the latter opposite. To deal with the damping‐elasticity paradox, the advantage of pseudobinary eutectic reaction and rapid cooling of laser powder bed fusion is taken to fabricate a bulk NiTiSn nanocomposite with a two‐level hierarchical structure. The first‐level architecture is composed of martensitic NiTi nanolamellae and reinforced Ti 3 Sn nanolamellae. In addition to lattice strain matching and lamellar boundary strengthening, a novel mechanism of martensite reorientation mediated by reversible stress‐induced detwinning‐twinning is activated to generate large elastic strain. A high density of nanotwins and nanodomains within NiTi nanolamellae constitute the second‐level architecture, which provides pronounced internal friction for high damping capacity. As a result, our NiTiSn nanocomposite exhibits a record‐high integration of damping capacity (tanδ > 0.10) and elastic strain (exceeding 4.5%), as well as superb stability under cyclic overload. This research not only represents a major breakthrough in achieving HDAs with outstanding damping and elastic strain but also offers a novel paradigm for high‐performance functional and structural materials.

Chemistry↗

NASA NTRS1988

Tribological composition optimization of chromium-carbide-based solid lubricant coatings for foil gas bearings at temperatures to 650 C

The determination of the tribilogically optimum composition of chromium-carbide-based solid lubricant coatings using a foil gas bearing test apparatus is described. The coatings contain a wear resistant chromium carbide `base stock' with the lubricant additives silver and BaF2-CaF2 eutectic. The coating composition is optimized for air-lubricated foil gas bearings at temperatures ranging from 25 to 650 C. The various compositions were prepared by powder blending, then plasma sprayed onto Inconel 718 test journals and diamond ground to the desired coating thickness and surface finish. The journals were operated against preoxidized Ni-Cr alloy foils, and the test bearings were subjected to repeated start-stop cycles under a bearing unit of 14 kPa. Sliding contact between the coated journal and the smooth foil occurs during bearing start-up before lift-off or hydrodynamic lubrication by the air film and during bearing coast-down. The bearings were tested for 9000 start-stop cycles or until specimen reached a predetermined failure level.

Dellacorte, Christopher↗

NASA NTRS2007

Solidification Behavior of gamma'-Ni3Al Containing Alloys in the Ni-Al-O System

The chemical activities of Al and Ni in gamma(prime)-Ni3Al-containing systems were measured using the multi-cell Knudsen effusion-cell mass spectrometry technique (multi-cell KEMS), over the composition range 8 - 32 at.%Al and temperature range T = 1400 - 1750 K. From these measurements a better understanding of the equilibrium solidification behaviour of gamma(prime)-Ni3Al-containing alloys in the Ni-Al-O system was established. Specifically, these measurements revealed that (1) gamma(prime)-Ni3Al forms via the peritectiod reaction, gamma + Beta (+ A12O3) = gamma (prime) (+ Al2O3), at 1633 +/- 1 K, (2) the {gamma + Beta + Al2O3} phase field is stable over the temperature range 1633 through 1640 K, and (3) equilibrium solidification occurs by the eutectic reaction, L (+ Al2O3) = gamma + Beta (+ Al2O3), at 1640 +/- 1 K and a liquid composition of 24.8 +/- 0.2 at.%Al (at an unknown oxygen content). When projected onto the Ni-Al binary, this behaviour is inconsistent with the current Ni-Al phase diagram and a new diagram is proposed. This new Ni-Al phase diagram explains a number of unusual steady-state solidification structures reported previously and provides a much simpler reaction scheme in the vicinity of the gamma(prime)-Ni3Al phase field.

Copland, Evan↗

NASA NTRS2004

Self Assembled Structures by Directional Solidification of Eutectics

Interest in ordered porous structures has grown because of there unique properties such as photonic bandgaps, high backing packing density and high surface to volume ratio. Inspired by nature, biometric strategies using self assembled organic molecules dominate the development of hierarchical inorganic structures. Directional solidification of eutectics (DSE) also exhibit self assembly characteristics to form hierarchical metallic and inorganic structures. Crystallization of diphasic materials by DSE can produce two dimensional ordered structures consisting of rods or lamella. By selective removal of phases, DSE is capable to fabricate ordered pore arrays or ordered pin arrays. Criteria and limitations to fabricate hierarchical structures will be presented. Porous structures in silicon base alloys and ceramic systems will be reported.

Dynys, Frederick W.↗

NASA NTRS1987

Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 to 1400 K

Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat storage materials in advanced solar dynamic space power systems with operating temperatures in the range of 973 to 1400 K. The melting points and eutectic composition for many systems with published phase diagrams were verified, and several new eutectic compositions were identified. Additionally, the heats of fusion of several binary and ternary eutectics and congruently melting intermediate compounds were measured by differential scanning calorimetry. The extent of corrosion of various metals by fluoride melts was estimated from thermodynamic considerations, and equilibrium conditions inside a containment vessel were calculated as functions of the initial moisture content of the salt and free volume above the molten salt. Preliminary experimental data on the corrosion of commercial, high-temperature alloys in LiF-19.5CaF2 and NaF-27CaF2-36MgF2 melts are presented and compared to the thermodynamic predictions.

Misra, Ajay K.↗

NASA NTRS1987

Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 - 1400 K

Misra, Ajay K.↗

DOE OSTI2025

Shining light on nanoscale ‘vine-on-stick’ eutectic structures in the Al-Ce-Ni system

Multiphase eutectics often comprise entangled solid phases with nanoscale periodicity, making it difficult to unravel their 3D connectivity using conventional 2D techniques. Among such systems, the three-phase eutectic Al-Al 11 Ce 3 -Al 3 Ni stands out for its ultrafine (∼100 nm) interphase spacing and promising creep resistance, yet its microstructure remains relatively unexplored despite its potential for high-temperature applications. Here, we use scanning hard X-ray microscopy with an unprecedented ∼10 nm pixel size to resolve its 3D morphology. Reconstructions reveal a novel “vine-on-stick” motif, wherein Al 11 Ce 3 wraps around Al 3 Ni pillars. Analysis of phase tortuosities confirms that Al 11 Ce 3 exhibits more convoluted morphologies than Al 3 Ni. No orientation relationship was observed between the two intermetallics, suggesting that growth is controlled by local solute gradients rather than epitaxy. Fragmentation of intermetallics along their longitudinal axis suggests a Rayleigh-type breakup mechanism in solid state. The “vine-on-stick” pattern may generalize to other alloy systems with variable interfacial anisotropies and low mutual solubilities.

36 MATERIALS SCIENCE↗

NASA NTRS2009

NiF2/NaF:CaF2/Ca Solid-State High-Temperature Battery Cells

Experiments and theoretical study have demonstrated the promise of all-solid-state, high-temperature electrochemical battery cells based on NiF2 as the active cathode material, CaF2 doped with NaF as the electrolyte material, and Ca as the active anode material. These and other all-solid-state cells have been investigated in a continuing effort to develop batteries for instruments that must operate in environments much hotter than can be withstood by ordinary commercially available batteries. Batteries of this type are needed for exploration of Venus (where the mean surface temperature is about 450 C), and could be used on Earth for such applications as measuring physical and chemical conditions in geothermal wells and oil wells. All-solid-state high-temperature power cells are sought as alternatives to other high-temperature power cells based, variously, on molten anodes and cathodes or molten eutectic salt electrolytes. Among the all-solid-state predecessors of the present NiF2/NaF:CaF2/Ca cells are those described in "Solid-State High-Temperature Power Cells" (NPO-44396), NASA Tech Briefs, Vol. 32, No. 5 (May 2008), page 40. In those cells, the active cathode material is FeS2, the electrolyte material is a crystalline solid solution of equimolar amounts of Li3PO4 and LiSiO4, and the active anode material is Li contained within an alloy that remains solid in the intended high operational temperature range.

West, William↗

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↗

NASA NTRS1991

Containerless processing and rapid solidification of Nb-Si alloys of hypereutectic composition

A combination of bulk undercooling in an electromagnetic levitation apparatus and splat quenching between two copper plates is used to process Nb-Si alloys in order to maximize rapid solidification conditions and minimize the effects of recalescence, with emphasis on the solidification of characteristics of alloys in the 21 to 27 at. pct Si range of composition. SEM and TEM as well as X-ray diffraction are used to characterize the microstructures of the processed samples. In the range of compositions studied, the splat-quenched drops always formed the tetragonal Nb3Si phase directly from the liquid. Drops solidified in the coil were characterized by the presence of the primary intermetallic Nb5Si3 and the absence of both peritectic Nb3Si and the equilibrium eutectic. In these cases, a metastable alpha-Nb + beta-Nb5Si3 eutectic formed. The results are discussed in terms of possible metastable configurations of the Nb-Si phase diagram as well as concepts of nucleation and growth kinetics applied to the Nb3Si and Nb5Si3 intermetallics.

Hofmeister, W. H.↗

NASA NTRS1986

Gravitational macrosegregation in binary Pb-Sn alloy ingots

A space shuttle experiment employing the General Purpose (Rocket) Furnace (GPF) in its isothermal mode of operation is manifested on MSL-3, circa 1989. The central aim of this experiment is to investigate the effect of reduced gravity levels on the segregation behavior in a slowly, and isothermally, cooled sample of a binary Pb-15 wt% Sn alloy. This experiment should be able to simulate, in a small laboratory sample, some aspects of the segragation phenomena occurring in large industrial ingots. Ground-based experiments conducted in the single-cavity simulator of the GPF, in support of the microgravity experiment are described in detail. The results of the MSFC experiments are compared with other related experiments conducted at Case Western Reserve University (CWRS), wherein the isothermal constraints were relaxed. The isothermally processed samples indicate a small and gradual increase in fraction eutectic, and a corresponding increase in tin content, from the bottom to the top of the ingot. The radial variations are minimal near the ingot bottom, but there are large radial variations in the top half. In the CWRU experiments, more severe segregations, including segregation defects known as freckles. Follow up experiments employing the GPF without the isothermal constraints, or other suitably modified space shuttle hardware are suggested.

Laxmanan, V.↗

NASA NTRS1987

Gravitational macrosegregation in binary Pb-Sn alloy ingots

A space shuttle experiment employing the General Purpose (Rocket) Furnace (GPF) in its isothermal mode of operation is manifested on MSL-3, circa 1989. The central aim of this experiment is to investigate the effect of reduced gravity levels on the segregation behavior in a slowly, and isothermally, cooled sample of a binary Pb-15 wt pct Sn alloy. This experiment should be able to simulate, in a small laboratory sample, some aspects of the segregation phenomena occurring in large industrial ingots. Ground-based experiments conducted in the single-cavity simulator of the GPF, in support of the microgravity experiment are described in detail. The results of the MSFC experiments are compared with other related experiments conducted at Case Western Reserve University (CWRS), wherein the isothermal constraints were relaxed. The isothermally processed samples indicate a small and gradual increase in fraction eutectic, and a corresponding increase in tin content, from the bottom to the top of the ingot. The radial variations are minimal near the ingot bottom, but there are large radial variations in the top half. In the CWRU experiments, more severe segregations, including segregation defects known as freckles. Follow up experiments employing the GPF without the isothermal constraints, or other suitably modified space shuttle hardware are suggested.

Laxmanan, V.↗

NASA NTRS1984

Studies of directionally solidified eutectic Bi/MnBi at low growth velocities

The (lambda-squared)(V) deviation for diffusion-only rod eutectic growth, where lambda is the interrod spacing and V is the growth velocity, was studied at growth velocities less than 5 cm/h in directionally solidified eutectic Bi-Mn (Bi/MnBi). At lower growth velocities, (V less than 0.5 cm/h) morphological instability occurred which resulted in nonaligned, irregularly dispersed MnBi fibers. The (lambda-squared)(V) relation was experimentally determined over a range of growth velocities between 0.1 and 50 cm/h, thermal gradients in the liquid at the liquid-solid interface that varied from 40 to 120 C/cm and solidification orientation with respect to the direction of gravity. Naturally induced, convective instabilities are suggested as a possible growth velocity limit for cooperative growth in the Bi-Mn and related alloy systems.

Pirich, R. G.↗

DOE OSTI2025

Mitigated Dissimilar Mass Transfer with Aluminized RAFM Steels in Flowing PbLi at 650°C

To evaluate dissimilar material interactions in flowing eutectic Pb-16at. %Li between fusion-relevant materials and to establish a maximum operating temperature of future blanket designs, a series of thermal convection loop (TCL) experiments with flowing PbLi have been conducted. Following a 1000-h, 550°C to 650°C TCL experiment, a thin reaction product was observed on the surface of monolithic, high-purity SiC. To identify the source of the observed dissimilar material interaction and to understand the reaction kinetics, an identical 2000-h TCL exposure was conducted, but less reaction of the SiC specimen was observed. Characterization of the FeCrAlMo (alloy APMT) loop tubing and the PbLi-exposed austenitic stainless steel (SS) assembly parts suggested that the formation of the reaction layer on the surface of the PbLi-exposed SiC did not originate from the coated reduced activation ferritic martensitic (RAFM) steel, but from the dissolved loop materials (liquid metal exposed APMT tubing and type 316 SS fittings). Here, the results, after 2000 h, suggest that the dissimilar material reaction between the Al-coated RAFM steel and the SiC has very slow reaction kinetics within a temperature gradient of 550°C to 650°C.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS2008

Solid-State High-Temperature Power Cells

All-solid-state electrochemical power cells have been fabricated and tested in a continuing effort to develop batteries for instruments for use in environments as hot as 500 C. Batteries of this type are needed for exploration of Venus, and could be used on Earth for such applications as measuring physical and chemical conditions in geothermal and oil wells, processing furnaces, and combustion engines. In the state-of-the-art predecessors of the present solid-state power cells, fully packaged molten eutectic salts are used as electrolytes. The molten-salt-based cells can be susceptible to significant amounts of self-discharge and corrosion when used for extended times at elevated temperatures. In contrast, all-solid-state cells such as the present ones are expected to be capable of operating for many days at temperatures up to 500 C, without significant self-discharge. The solid-state cell described here includes a cathode made of FeS2, an electrolyte consisting of a crystalline solid solution of equimolar amounts of Li3PO4 and Li4SiO4, and an anode made of an alloy of Li and Si (see figure). The starting material for making the solid electrolyte is a stoichiometric mixture of Li3PO4, SiO2, and Li3CO2. This mixture is ball-milled, then calcined for two hours at a temperature of 1,100 C, then placed in a die atop the cathode material. Next, the layers in the die are squeezed together at a pressure between 60 and 120 MPa for one hour at a temperature of 600 C to form a unitary structure comprising the solid electrolyte and cathode bonded together. Finally, the lithium-alloy anode is pressure-bonded to the solid electrolyte layer, using an intermediate layer of pure lithium. In one test of a cell of this type, a discharge rate of about 1 mA per gram of cathode material was sustained for 72 hours at a temperature of about 460 C. This is about three times the discharge rate required to support some of the longer duration Venus-exploration mission scenarios.

Whitacre, Jay↗

NASA NTRS1984

The solidification of monotectic alloys - Microstructures and phase spacings

The microstructures of directionally grown monotectic alloys in metallic and organic systems fall into two categories those which can form aligned fibrous composite structures with even phase spacings and fiber sections, and those in which the phase distribution is coarser and less regular. This division appears to relate to the form of the phase diagram and has been rationalized by Cahn (1977, 1979) in terms of the relative surface energies between solid and two liquids to give steady state or nonsteady state profiles. The transition in growth behavior occurs when the ratio of the monotectic temperature to that of the upper consolute temperature is approximately 0.9. Differences in phase spacings between a range of monotectic and eutectic systems are discussed in terms of the expected growth interface shapes and the factors which will influence them.

Grugel, R. N.↗

DOE OSTI2024

High-Pressure Melting Experiments of Fe 3 C and a Thermodynamic Model of Fe-C Liquids for the Earth's Core

Melting experiments of Fe 3 C were conducted to 85 GPa in laser-heated diamond anvil cells with in situ X-ray diffraction and post-experiment textural observation. From the determined pressure-temperature conditions of the melting curve for Fe 3 C, together with literature data on the melting point of diamond and eutectic point of the system Fe-Fe 3 C/Fe 7 C 3 under high pressures, we established a self-consistent thermodynamic model for high-pressure melting of the system Fe-C including the mixing parameters for liquids. The results show that mixing of Fe and C liquids is negatively nonideal from 1 bar to the pressure at the center of the Earth. The departure from ideal mixing becomes progressively larger with increasing pressure, which leads to greatly stabilized liquids under core pressures. The modeled carbon content in eutectic melts under core pressures is 3.3–4.4 wt%. From the Gibbs free energy, we derived an internally consistent parameters for Fe-C outer cores which included the crystallizing points at their bottoms, isentropic thermal profiles, and densities and longitudinal seismic wave speeds (Vp). While the addition of carbon in excess of the eutectic melt composition effectively reduces the density of iron liquid, the Vp of iron liquid is not greatly changed. Therefore, the low density and high Vp of PREM relative to pure iron cannot be reconciled by an Fe-C liquid. Therefore, the Earth's core cannot be approximated by the system Fe-C and should include another light element.

58 GEOSCIENCES↗

DOE OSTI2024

Microstructure analysis and machinability of additively manufactured A205 aluminum with heat treatments

A205 aluminum is one of the few high-strength aluminum alloys discovered for additive manufacturing (AM). The microstructure and heat treatment effects of AM A205 vary from those of its cast form, indicating possible differences in machinability during post-processing. Here, the objective of this research is to determine these variations of AM A205 and their effects on machinability using the cast condition as the baseline. As built and two heat-treated conditions (solution treatment and age hardening) were applied and compared in terms of their microstructures, micro-hardness, and machinability including vibration, specific cutting energy, chip morphology, and surface finish. The effects of print orientations on machinability were tested as well and found to be insignificant. AM as built had a higher hardness and slightly better machinability than its cast as built cast counterpart due to a smaller grain size (1 µm vs. 15 µm), eutectic θ-Al 2 Cu lattice and a fine, homogeneous TiB 2 distribution. The solution treatment dissolved this θ-Al 2 Cu lattice and increased the grain size (3 µm) which decreased the hardness, increased the ductility seen in the chips, and reduced the overall machinability. The presence of θ’-Al 2 Cu precipitates improved the machinability of aged AM A205. In addition, it was found that A205 exhibited both ductile and brittle behavior depending on the cutting speed, thus producing different machinability. The speed dependency is related to the material condition and heat treatment.

36 MATERIALS SCIENCE↗