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Results for “metallic glasses”

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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Atomic imprinting in the absence of an intrinsic length scale

Bulk metallic glasses (BMGs) have successfully been used to replicate molds that are structured at the nano- and even atomic scale through thermoplastic forming (TPF), an ability that was speculated to be rooted in the glass’ featureless atomic structure. These previous demonstrations of atomically precise imprinting, however, were performed under conditions where mold atomic feature dimensions coincided with the unit cell size of constituents in the BMG. In order to evaluate if accurate atomic-scale replication is possible in general, i.e., independent of the accidental presence of favorable constituent size/feature size relationships, we have used Pt 57.5 Cu 14.7 Ni 5.3 P 22.5 to replicate three different crystalline facets of LaAlO 3 single crystals, each exposing distinct atomic step heights. We find that in all cases, the terraced surface termination can be copied with remarkable fidelity, corroborating that BMGs when thermoplastic formed are capable of adapting to any externally imposed confinement with sub-angstrom precision without being limited by factors related to the specifics of their internal structure. This unprecedented capability of quasi-limitless replication fidelity reveals that the deformation mechanism in the supercooled liquid state of BMGs is essentially homogeneous and suggests TPF of BMGs to be a versatile toolbox for atomic and precision nanoscale imprinting.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Sputtered Au–Ta films with tunable electrical resistivity

Gold–tantalum alloy films are attractive for hohlraums used in indirect drive magnetized inertial confinement fusion. A high electrical resistivity of over ~100 µΩ cm at cryogenic temperatures is an essential requirement for allowing an externally imposed pulsed magnetic field to soak through a hohlraum and magnetize the fusion fuel. In this work, we systematically study properties of Au–Ta alloy films in the entire compositional range from pure Au to pure Ta with thicknesses up to 30 µm. These films are made by direct current magnetron co-sputtering on planar substrates. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, nanoindentation, and electrical transport measurements. Results show that an alloy with ~80 at.% of Ta forms a metallic glass exhibiting a maximum electrical resistivity of ~300 µΩ cm with a weak temperature dependence in the range of 5–400 K. The deposition of a film with ~80 at.% of Ta onto a sphero-cylindrical substrate for hohlraum fabrication is also demonstrated.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Intrinsic anharmonicity and thermal properties of ultralow thermal conductivity Ba 6 Sn 6 Se 13

Ultralow thermal conductivity materials continue to be of great interest for technologically important applications such as thermal insulators and thermoelectrics. Often, such materials possess constituents with extensive dynamic disorder, or “rattlers,” or structural disorder such as metallic glasses. Nevertheless, targeted crystalline bonding order and anharmonicity can provide effective means for the scattering of the phonons in certain materials. Our combined experimental and theoretical investigation of Ba 6 Sn 6 Se 13 reveals such a material, with ultralow thermal conductivity measured over a large temperature range. Optic phonon modes hybridize with acoustic modes at relatively low energies resulting in strong acoustic-optic scattering and limited phonon lifetimes. Moreover, our investigations reveal various avoided crossings at low energies that contribute to phonon scattering. These are derived from chiral phase symmetries and may result in nontrivial topological behaviors for phonon band crossings in this chiral material. This work contributes to the ongoing research on low thermal conductivity materials and the underlying mechanisms that affect their thermal behaviors. Manipulation of these effects may provide pathways for enhancement of material properties for targeted thermal applications using similar materials.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Sputtering: A vacuum deposition method for coating material

The sputtering process is described in terms of its features: versatility, momentum transfer, configuration of target, precise controls and the relatively slow deposition rate. Sputtered films are evaluated in terms of adherence, coherence, and internal stresses. The strong adherence is attributed to the high kinetic energies of the sputtered material, sputter etched (cleaned) surface, and the submicroscopic particle size. An illustration is a sputtered solid film lubricant such as MoS2. Friction tests were conducted on a thin, 2000 A deg thick MoS2 film. These films are very dense and without observable pinholes, and the particle to particle cohesion is strong. Tolerances (film thickness) can be controlled to a millionth of a centimeter. Very adherent films of sputtered Teflon can be deposited in a single operation on any type of material (metal, glass, paper) and on any geometrical configuration with a dense adherent film.

Spalvins, T.↗
NASA NTRS1974

Detection of cracks in surface insulation

Volatile organic liquid surface penetrants used with appropriate detector paper leave tested surfaces uncontaminated. Method can be used to detect minute cracks in materials such as metal, glass, plastics, ceramics, etc.

Leger, L. J.↗
NASA NTRS1967

Infusible silazane polymer and process for producing same

Coatings of high thermal and chemical stability for application to metal, glass, ceramics, and other surfaces are formed by reacting diphenyldichlorosilane in the presence of triethylamine with a nitrogen base selected from the group consisting of ammonia and methylamine. The pl polymeric, noncrystalline reaction product is heated in a reaction zone open to the atmosphere at a temperature ranging from approximately 250 C to 450 C until the infusible polymer is formed.

Burks, R. E., Jr.↗
NASA NTRS1979

Performance characteristics and statistics of a laser initiated microdetonator

The test results of 320 units of the laser initiated microdetonator are summarized. The commercially fabricated units used a lead styphnate/lead azide/HMX (1 mg/17.5 mg/13.5 mg) explosive train design contained in a miniature aluminum can and completed with a glass-metal seal window. The test parameters were the high and low laser energy, high and low temperature, laser pulse duration, laser wavelength and nuclear radiation (5 x 10 to the 6th rads of 1 MeV gamma ray). The performance parameters were the laser energy for ignition and the actuation response time. Included also is a description of the development of a flexible, continuously advanced train of explosive devices by using the units, miniature optics and fiber optics.

Yang, L. C.↗
NASA NTRS1980

Development of a trash handling subsystem for a manned spacecraft

A prototype laboratory system to shred and transport trash material within a spacecraft was designed and demonstrated. In addition to handling the normal trash materials, the system demonstrated the ability to handle or reject (if it is too tough) glass, metal and ceramics without damaging the system. The system is not dependent on liquids for the shredding and transportation and can transport slurried, damp or dry material. The resulting system offers a greater system flexibility with operational reliability.

Burnett, M.↗
NASA NTRS1980

U.S. program assessing nuclear waste disposal in space - A status report

Various concepts for the space disposal of nuclear waste are discussed, with attention given to the destinations now being considered (high earth orbit, lunar orbit, lunar surface, solar orbit, solar system escape, sun). Waste mixes are considered in the context of the 'Purex' (Plutonium and Uranium extraction) process and the potential forms for nuclear waste disposal (ORNL cermet, Boro-silicate glass, Metal matrix, Hot-pressed supercalcine) are described. Preliminary estimates of the energy required and the cost surcharge needed to support the space disposal of nuclear waste are presented (8 metric tons/year, requiring three Shuttle launches). When Purex is employed, the generated electrical energy needed to support the Shuttle launches is shown to be less than 1%, and the projected surcharge to electrical users is shown to be slightly more than two mills/kW-hour.

Rice, E. E.↗
NASA NTRS1980

Recent work on use of lunar materials for SPS construction

The feasibility of mounting a small operation on the Moon to productively use lunar materials in support of programs such as the solar power satellite is addressed. A cost effective scenario of a small chemical process plant on the surface of the Moon and a small machine shop located in orbit is presented. The mass of the space installation is compared to the projected outputs in 90 days. It is indicated that the system would have the capability of replicating about 90% of its own components and would provide the metals, glasses, and silicon needed for the contruction of 90% to 96% of the mass of one solar power satellite per year.

Oneill, G. K.↗
NASA NTRS1981

Space Shuttle - A new era in transportation

After a brief historical review of the economics of expendable-booster, commercial-payload operations to date, and a description of the Space Shuttle system's design, operational capabilities, and mission profile, the payload flight assignments, materials processing experiments, and Spacelab I material science experiment are detailed. Among the Materials Processing in Space (MPS) fields for investigation are crystal growth from vapor and solution, the production of magnetic composites and metal foams, laser host glasses and metallic glasses, non-buoyancy-driven convections, unidirectional solidification of eutectics, and the solidification of immiscible alloys. Emphasis is put on the long-term, commercial usefulness of such studies, with attention to historical precedents such as the Skylab, Apollo and Apollo-Soyuz programs.

Dunbar, B. J.↗
NASA NTRS1981

Performance characteristics of a laser initiated microdetonator

The test results of 320 units of a laser initiated microdetonator are summarized. The commercially fabricated units used a lead styphnate/lead azide/HMX (1 mg/13.5 mg) explosive train design contained in a miniature aluminum can that was capped with a glass-metal seal window. The test parameters were the laser energy, temperature, laser pulse duration, laser wavelength and nuclear radiation (5,000,000 rad of 1 MeV gamma rays). The performance parameters were the laser energy for ignition and the actuation response time.

Yang, L. C.↗
NASA NTRS1982

Origin of rapidly solidified metal-troilite grains in chondrites and iron meteorites

Quantitative evidence is adduced by cooling rate calculations for the impact melting, on the surface of a parent body, of troilite and metallic Fe, Ni inclusions found on 12 ordinary chondrites rather than their formation at depth from an internally derived melt. In the case of the Shaw and Rose City breccias of unmelted and melted material, their melted metal need not have cooled through 1000 C within a few meters of the surface. Shock-melted, fine-grained, irregular intergrowths of metal and troilite form in situ in many irons and some chondrites by rapid solidification at cooling rates greater than 100,000 C/sec, so that their kamacite and taenite compositions may result from annealing of metallic glass or very fine quench products at about 250 C.

Scott, E. R. D.↗
NASA NTRS1982

Application of microgravity and containerless environments to the investigation of fusion target fabrication technology

After the first observation of the core-centering force within a liquid shell in the KC-135 flight experiment, this force was successfully reproduced in terrestrial laboratories using two experimental techniques. The core-centering force generated for a compound drop system in the neutral buoyancy tank provides the first correlation between theoretical and experimental results. When this force was generated in a more realistic fusion-pellet system using the focusing-radiator levitating system, it was shown that this is a very strong force indeed in view of the fact that the ratio of specific gravities between the water and the core is approximately five. It is believed that this centering force will contribute significantly to an overall understanding of the fabrication physics of a fusion target system. Results from experiments in a vertical drag-free wind tunnel and in a 16-ft low pressure drop furnace suggest that eliminating or reducing the aerodynamic drag on fusion pellets during their formation stage will prevent the decentering of the bubble. Metallic and metallic glass fusion targets are seen as holding promise for improving and simplifying the fabrication process for ablative-type fusion targets.

Lee, M. C.↗
NASA NTRS1984

The potential for bulk undercooling as an industrial process

The main focus is on solidification occurring in highly supercooled melts. Solidification rates in such melts are extremely high, an attractive feature from a commercial standpoint. Thus, the reported growth velocities for pure Ni and Co dendrites at a supercooling of 175 K are in excess of 180 km/hr. Rapidly quenched crystalline alloys produced by various atomization processes (e.g., centrifugal atomization or inert gas atomization) or melt spinning are examples of solidification processes, currently being intensively explored commercially, wherein extremely high solidification rates are achieved. Estimated dendrite tip growth rates are about 2 km/hr in a binary Al-4.5 wt % alloy, with a heat transfer coefficient of 6.4x10 sub 5 w/sq cm K or 15 cal/cu cm sK. In the limit, when the solidification rate exceeds a critical value, a glassy microstructure is obtained even in highly alloyed melts, which under normal conditions would solidity to form one or more crystalline phases. Glassy metals, also called metallic glasses, are candidate materials for distribution transformers because of their very low energy losses and are also being used in brazing and soldering applications.

Laxmanan, V.↗
NASA NTRS1983

Crystal nucleation in amorphous (Au/100-y/Cu/y/)77Si9Ge14 alloys

Because, unlike most metallic glasses, melt-spun alloys of the series (Au/100-y/Cu/y/)77Si9Ge14 exhibit well separated glass transition and kinetic crystallization temperatures, crystallization can be studied in the fully relaxed amorphous phase. An isothermal calorimetric analysis of the devitrification kinetics of the amorphous alloy indicates sporadic nucleation and a constant growth rate. It is found for the cases of alloys with y values lower than 25 that the classical theory of homogeneous nucleation is consistent with observations, including transient effects. An analysis of the crystallization kinetics shows that slow crystal growth rates play an important role in glass formation in these alloys. Although the reduced glass transition temperature increases with Cu content, glass formation is more difficult at high Cu contents, perhaps because of a difference in nucleus composition.

Thompson, C. V.↗
NASA NTRS1986

Analytical ultrasonics for characterization of metallurgical microstructures and transformations

The application of contact (piezoelectric) and noncontact (laser generation and detection) ultrasonic techniques for dynamic investigation of precipitation hardening processes in aluminum alloys, as well as crystallization and phase transformation in rapidly solidified amorphous and microcrystalline alloys is discussed. From the variations of the sound velocity and attenuation the precipitation mechanism and kinetics were determined. In addition, a correlation was established between the observed changes in the velocity and attenuation and the mechanical properties of age-hardenable aluminum alloys. The behavior of the elastic moduli, determined ultrasonically, were found to be sensitive to relaxation, crystallization and phase decomposition phenomena in rapidly solidified metallic glasses. Analytical ultrasonics enables determination of the activation energies and growth parameters of the reactions. Therefrom theoretical models can be constructed to explain the changes in mechanical and physical properties upon heat treatment of glassy alloys. The composition dependence of the elastic moduli in amorphous Cu-Zr alloys was found to be related to the glass transition temperature, and consequently to the glass forming ability of these alloys. Dynamic ultrasonic analysis was found to be feasible for on-line, real-time, monitoring of metallurgical processes.

Rosen, M.↗