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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Directional solidification of Pb-Sn eutectic with vibration

Pb-Sn eutectic alloy was directionally solidified at 1.4 to 3.2 cm/h with forced convection induced by axial vibration of the growth ampoule with a frequency of 10 to 40 Hz and an amplitude of 0.5 to 1.0 mm. To determine the exact growth rate, an interface demarcation technique was applied. The lamellar spacing was increased 10 to 40 percent in ingots solidified with vibration, compared to those solidified without vibration. The number of grain boundaries was increased by vibration. The average intensity of convection in the melt under axial vibration of the ampoule was estimated by comparing the experimental results with a theoretical model.

Caram, Rubens↗
NASA NTRS1998

Thin Film Mediated Phase Change Phenomena: Crystallization, Evaporation and Wetting

We focus on two distinct materials science problems that arise in two distinct microgravity environments: In space and within the space of a polymeric network. In the former environment, we consider a near eutectic alloy film in contact with its vapor which, when evaporating on earth, will experience compositionally induced buoyancy driven convection. The latter will significantly influence the morphology of the crystallized end member. In the absence of gravity, the morphology will be dominated by molecular diffusion and Marangoni driven viscous flow, and we study these phenomena theoretically and experimentally. The second microgravity environment exists in liquids, gels, and other soft materials where the small mass of individual molecules makes the effect of gravity negligible next to the relatively strong forces of intermolecular collisions. In such materials, an essential question concerns how to relate the molecular dynamics to the bulk rheological behavior. Here, we observe experimentally the diffusive motion of a single molecule in a single polymer filament, embedded within a polymer network and find anomalous diffusive behavior.

Wettlaufer, John S.↗
NASA NTRS2000

Role of Vibration-Induced Streaming in Float-Zone Crystal Growth

This presentation will examine in detail the role of vibration-induced streaming flow in the context of float-zone crystal growth. It is very well known that during float-zone materials processing, the naturally occurring temperature gradients along the zone surface impose a thermocapillary flow in the zone. Under certain processing conditions, the thermocapillary flow can also become nonsteady (oscillatory). The presence of thermocapillary flow is detrimental to crystal quality, for it can promote non-uniform dopant distribution and crystal striations. To null this effect we have imposed a counter streaming flow in the zone, via end-wall vibration. This technique has been adapted to float-zone processing of Sodium Nitrate-Barium Nitrate eutectic alloys, under both steady and nonsteady thermocapillary flow conditions. The beneficial effects of counter streaming flow have been clearly brought out through the before and after comparisons of the crystal microstructure. In addition, we are also examining the theoretical underpinnings of the balancing of thermocapillary flows with vibration-driven counter flows in float-zones.

Anilkumar, A. V.↗
NASA NTRS2001

Role of Vibration-Induced Streaming in Float-Zone Crystal Growth

This presentation will examine in detail the role of vibration-induced streaming flow in the context of float-zone crystal growth. It is very well known that during float-zone materials processing, the naturally occurring temperature gradients along the zone surface impose a thermocapillary flow in the zone. Under certain processing conditions, the thermocapillary flow can also become nonsteady (oscillatory). The presence of thermocapillary flow is detrimental to crystal quality, for it can promote non-uniform dopant distribution and crystal striations. To null this effect we have imposed a counter streaming flow in the zone, via end-wall vibration. This technique has been adapted to float-zone processing of Sodium Nitrate-Barium Nitrate eutectic alloys, under both steady and nonsteady thermocapillary flow conditions. The beneficial effects of counter streaming flow have been clearly brought out through the before and after comparisons of the crystal microstructure. In addition, we are also examining the theoretical underpinnings of the balancing of thermocapillary flows with vibration-driven counter flows in float-zones.

Anikumar, A. V.↗
NASA NTRS2004

Coarsening in Solid-Liquid Mixtures-2: A Materials Science Experiment for the ISS

A materials science experiment has been developed and readied for operation aboard the International Space Station (ISS). Components of this experiment are onboard ISS and area awaiting the flight of science samples. The goal of the experiment is to understand the dynamics of Ostwald ripening, also known as coarsening, a process that occurs in nearly any two-phase mixture found in nature. Attempts to obtain experimental data in ground-based laboratories are hindered due to the presence of gravity, which introduces material transport modes other than that of the coarsening phenomenon. This introduces adjustable parameters in the formulation of theory. The original Coarsening in Solid-Liquid Mixtures (CSLM) mission, which flew on the Space Shuttle in 1997, produced data from a coarsened eutectic alloy. Unfortunately, both the science matrix and the hardware, while nominally functional, did not account adequately for operations in microgravity. A significantly redesigned follow-on experiment, CSLM-2 has been developed to redress the inadequacies of the original experiment. This paper reviews the CSLM-2 project: its history, science goals, flight hardware implementation, and planned operations and analysis

Hickman, J. Mark↗
DOE OSTI2026

Phase Transitions of Eutectic High Entropy Alloy AlCoCrFeNi 2.1 Under Shock Compression

High entropy alloys (HEAs) are a new class of metals that exhibit unique mechanical performance. Among HEAs, additively manufactured eutectic high entropy alloys (AM EHEAs) have recently emerged as candidate materials for use in extreme conditions due to their simultaneous high strength and ductility. However, the deformation and structural evolution of AM EHEAs under conditions of high pressure have not been well characterized, limiting their use in extreme applications. Dynamic compression experiments and molecular dynamics simulations are presented to study the structural evolution of AM EHEA AlCoCrFeNi 2.1 when compressed to pressures up to 400 GPa. In situ X-ray diffraction measurements capture the appearance of face-centered cubic and body-centered cubic phases at different pressure conditions, with pure- and mixed-phase regions. Furthermore, understanding the phase stability and structural evolution of the AM EHEA offers new insights to guide the development of high-performance complex materials for extreme conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Supercooling effects in faceted eutectic Nb-Si alloys

The effect of melt supercooling on the microstructure of an Nb-58 at. pct Si alloy is investigated experimentally using an electromagnetic levitation apparatus. It is found that, starting with an alloy nominally of eutectic composition, nucleation of Nb5Si3 occurs in the supercooled liquid first. Upon further cooling, the remaining liquid continues to supercool until the second phase, NbSi2 is nucleated, which is commonly accompanied by rapid recalescence. The primary phase exibits a eutectoid-type decomposition. The observations are discussed with reference to the results of quantitative microstructural measurements, compositional and thermal analysis, and preliminary thermodynamic modeling of the phase diagram.

Gokhale, A. B.↗
DOE OSTI2025

Eutectic melting of alloy microparticles upon low velocity impact

Although impact melting has been quantified in a number of pure metals, alloyed microparticles have access to low melting-point eutectics that can promote earlier melting. Through real-time monitoring of single particle impacts resolved at the nanosecond- and micron-scales, we explore the impact melting of AA7075 from high velocities, where it is abundant and clear, to velocities as low as ∼269 m/s. Here, by using a hard substrate to isolate the deformation largely to the particle, we show that the adiabatic heat produced by the plasticity of the impact can explain the onset of melting at low velocity.

Additive manufacturing↗
NASA NTRS1986

Undercooled and rapidly quenched Ni-Mo alloys

Hypoeutectic, eutectic, and hypereutectic nickel-molybdenum alloys were rapidly solidified by both bulk undercooling and melt spinning techniques. Alloys were undercooled in both electromagnetic levitation and differential thermal analysis equipment. The rate of recalescence depended upon the degree of initial undercooling and the nature (faceted or nonfaceted) of the primary nucleating phase. Alloy melts were observed to undercool more in the presence of primary Beta (NiMo intermetallic) phase than in gamma (fcc solid solution) phase. Melt spinning resulted in an extension of molybdenum solid solubility in gamma nickel, from 28 to 37.5 at % Mo. Although the microstructures observed by undercooling and melt spinning were similar the microsegregation pattern across the gamma dendries was different. The range of microstructures evolved was analyzed in terms of the nature of the primary phase to nucleate, its subsequent dendritic growth, coarsening and fragmentation, and final solidification of interfenderitic liquid.

Tewari, S. N.↗
NASA NTRS1987

Undercooled and rapidly quenched Ni-Mo alloys

Hypoeutectic, eutectic, and hypereutectic nickel-molybdenum alloys were rapidly solidified by both bulk undercooling and melt spinning techniques. Alloys were undercooled in both electromagnetic levitation and differential thermal analysis equipment. The rate of recalescence depended upon the degree of initial undercooling and the nature (faceted or nonfaceted) of the primary nucleating phase. Alloy melts were observed to undercool more in the presence of primary Beta (NiMo intermetallic) phase than in gamma (fcc solid solution) phase. Melt spinning resulted in an extension of molybdenum solid solubility in gamma nickel, from 28 to 37.5 at. pct Mo. Although the microstructures observed by undercooling and melt spinning were similar, the microsegregation pattern across the gamma dendries was different. The range of microstructures evolved was analyzed in terms of the nature of the primary phase to nucleate, its subsequent dendritic growth, coarsening and fragmentation, and final solidification of interfenderitic liquid.

Tewari, S. N.↗
DOE OSTI2025

Unravelling Microstructure Selection in an Additively Manufactured Eutectic High‐Entropy Alloy

High-entropy alloys (HEAs) are promising candidates for advanced structural applications due to their excellent mechanical properties. Additive manufacturing (AM), with its rapid solidification conditions, enables the creation of unique nonequilibrium microstructures. To fully leverage the synergy between AM and HEAs, understanding how processing affects structure and properties is essential. Here, how solidification rate influences microstructure evolution and phase transformation pathway in laser additively manufactured AlCrFe2Ni2 eutectic HEAs is investigated. By increasing the laser scan speed and hence the solidification rate, distinct solidification modes evolving from coupled eutectic to anomalous eutectic and eventually to single-phase solidification are revealed. These transitions result in distinct microstructures and a wide range of mechanical properties. Thermodynamic modeling and molecular dynamics simulations reveal that low cooling rates allow for sufficient atomic diffusion and phase separation, facilitating coupled eutectic growth. In contrast, rapid cooling suppresses diffusion and destabilizes the solid–liquid interface, promoting anomalous or single-phase solidification. This integrated experimental and computational approach provides a multiscale understanding of solidification mechanisms in HEAs and underscores how kinetic effects can over-ride thermodynamic predictions under nonequilibrium conditions. Furthermore, these results demonstrate that AM can serve as a powerful tool to design HEAs with tailored microstructures and properties.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Evaluation of high-temperature properties of binary, eutectic Ni-X alloys (X = B, Ca, Ce, La, Y, Zr)

We investigated the high-temperature behavior of binary eutectic nickel-base alloys with low-solubility elements, towards developing alloys with new combinations of structural and functional (e.g. thermal or corrosion) properties. Based on thermodynamic screening, we cast binary near-eutectic Ni-B, Ni-Ca, Ni-Ce, Ni-La, Ni-Y, and Ni-Zr alloys and characterized their microstructure and high-temperature properties. All alloys (except Ni-Ca) contain a fine eutectic microstructure, containing submicron alternating lamellae of γ-Ni and continuous intermetallic phases. The eutectic microstructure did not significantly coarsen at 700°C (except for Ni-B), but measurably coarsened in all alloys at 900°C, most quickly in Ni-B, followed by Ni-Ce, Ni-La, Ni-Y, and Ni-Zr. Coarsening in these alloys occurs by fault migration; diffusion within the intermetallic, and its interfacial energy, likely influence coarsening kinetics. At room-temperature, all alloys possess negligible ductility due to the continuous, brittle intermetallic. At 700 and 900°C, the Ni-Zr alloy showed the best combination of strength and ductility. Oxidation experiments at 900°C on Ni-Zr and Ni-Ce revealed heavy internal oxidation of the continuous intermetallic phase. Overall, the Ni-Zr alloy showed good high-temperature coarsening resistance and strength, though ductility and oxidation resistance require improvement for use in structural applications. Possible routes for improving alloy properties via additive manufacturing are discussed.

Ekaputra, Clement [ORNL] (ORCID:0000000307166479)↗
NASA NTRS1977

Determining eutectic composition in metal alloys

Tube crucible and furnace are used to separate eutectic mixture from trial-melt ingot. As ingot is a slowly heated to melting point, initial surface meeting will be eutectic mixture. Molten metal is collected at bottom of crucible, where it is solidified.

Ashbrook, R. L.↗
DOE OSTI2024

Systematic discovery of new nano-scale metastable intermetallic eutectic phases in laser rapid solidified Aluminum-Germanium alloy

Laser surface remelting of as-cast Al-Ge eutectic alloy is shown to produce ultrafine lamellar eutectic morphology with interlamellar spacing refined up to ∼60 nm and composed of FCC Al solid solution and unusual Al x Ge y intermetallic phases that do not form during near-equilibrium solidification. The microstructures are characterized and analyzed using a combination of selected area electron diffraction, high-resolution scanning transmission electron microscopy, energy dispersive X-ray spectroscopy to obtain high-resolution elemental maps, and atomistic modeling using density functional theory followed by atomic-scale image simulation. Depending on the local solidification conditions, the crystallography of the Al x Ge y intermetallic phases in the eutectic microstructure is either monoclinic (C 2/c) or monoclinic (P 2 1 ), with high densities of defects in both cases. This is in sharp contrast to the as-cast alloys that showed nominally pure Al and Ge phases with significant solute partitioning and equilibrium FCC and diamond cubic crystal structures, respectively. Corresponding kinetic phase diagrams are proposed to interpret the evolution of nano-lamellar eutectic morphologies with equilibrium Al and metastable Al x Ge y phases, and to explain increased solid solubility in the Al phases manifested by precipitation of ultrafine clusters of Ge. Furthermore, the reasons for the formation of these metastable eutectics under laser rapid solidification are discussed from the perspective of the competitive growth criterion.

Al-Ge eutectic↗
NASA NTRS1982

Gravitationally induced convection during directional solidification of off-eutectic Mn-Bi alloys

The effects of thermal and solute gradient, gravity induced convection during vertical directional solidification, on longitudinal macrosegregation of Bi and Mn rich off-eutectic starting compositions, has been studied as a function of composition, growth velocity and gravity vector orientation. Since the morphology of these alloys is characterized by an aligned, rodlike permanent magnet composite when grown cooperatively, the magnetic properties were used to measure composition segregation and the transition from dendritic to composite growth. Severe macrosegregation was observed in all cases studied and the degree of convection inferred by modeling the observed composition segregation using a stagnant film approach. Morphological stability was found to follow a constitutional supercooling-type law for both Bi and Mn rich compositions.

Pirich, R. G.↗
DOE OSTI2025

Effect of Zr and Sc additions on coarsening- and creep resistance of AlSi10Mg fabricated by laser powder bed fusion

Microstructure and creep properties are studied in a eutectic AlSi10Mg alloy modified with Zr and Sc additions (Al-9.8Si-0.32Mg-0.70Zr-0.23Sc, wt%) manufactured through laser powder-bed fusion (L-PBF). Three types of Zr/Sc-bearing powders - elemental, master-alloy, and pre-alloyed - are employed in the fabrication process, with the pre-alloyed powders providing the highest incorporation of Zr and Sc in the Al matrix. Here, the as-printed alloy exhibits a fine cellular Al-Si eutectic structure which fragments and coarsens into micron-sized Si particles during aging at 300 ºC, leading to a steady drop in alloy microhardness between 0.1 and 1000 h. Coarsening of the eutectic Si phase during aging is not measurably affected by Zr and Sc in solid solution, which precipitate during aging and increases strength, compensating weakening from Si coarsening between 1 and 200 h at 300 ºC. Atom-probe analysis in the peak-aged condition (96 h/300 °C) confirms the presence of Al 3 (Sc,Zr) secondary nano-precipitates with an average radius of 1.0 nm and some Si solubility. Micron-sized grains are present throughout the alloy, with ultra-fine-grained regions at the melt pool boundaries, neither of which coarsen during long-term aging at 300 ºC. Under creep conditions at 300 °C, the Zr/Sc-bearing alloy with Al 3 (Sc,Zr) nano-precipitates exhibits power-law behavior, with a high apparent stress exponent (n a = 9) and a high threshold stress (σ th = 43 MPa), exhibiting nearly double the strength of a Zr/Sc-free AlSi10Mg control alloy (σ th = 22 MPa).

36 MATERIALS SCIENCE↗
DOE OSTI2026

Elevated-Temperature Tribo-Corrosion Response of Eutectic High-Entropy Alloy

The combination of elevated temperature and tribo-corrosion leads to the accelerated degradation of structural components used in many extreme environments. Recently developed high-entropy alloys (HEAs) with multiple principal elements have the potential for superior degradation resistance compared with presently used structural alloys. Here, we demonstrate the microstructural stability, pitting resistance, and superior tribo-corrosion degradation resistance of the AlCoCrFeNi 2.1 eutectic HEA in comparison with duplex stainless steel 2205 in deionized water (controlled low-ionic-strength electrolyte) at 25 °C, 50 °C and 100 °C. The AlCoCrFeNi 2.1 HEA showed excellent microstructural stability and tribo-corrosion resistance at all three temperatures, an order-of-magnitude lower wear rate, and a lower coefficient of friction compared with duplex 2205 steel. The lowest wear volume loss and wear rate for both AlCoCrFeNi 2.1 and duplex steel were recorded at 50 °C, which was attributed to temperature-assisted passivation and formation of a comparatively stable tribological surface condition. These results suggest superior performance of eutectic HEAs in tribo-corrosion applications compared with currently used dual-phase steels and motivate future evaluation in ion-containing industrial water chemistries.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Phase selection during crystallization of undercooled liquid eutectic lead-tin alloys

During rapid solidification substantial amounts of undercooling are in general required for formation of metastable phases. Crystallization at varying levels of undercooling and melting of metastable phases were studied during slow cooling and heating of emulsified PB-Sn alloys. Besides the experimental demonstration of the reversibility of metastable phase equilibra, two different principal solidification paths have been identified and compared with the established metastable phase diagram and predictions from classical nucleation theory. The results suggest that the most probable solidification path is described by the 'step rule' resulting in the formation of metastable phases at low undercooling, whereas the stable eutectic phase mixture crystallizes without metastable phase formation at high undercooling.

Fecht, H. J.↗