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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Microstructure and Properties of Mn-Cu-Based Damping Alloys Prepared by Ball Milling and Hot-Press Sintering

A Mn-Cu-based damping alloy with a nominal composition of 70Mn-24Cu-3Zn-3Al (at.%) was prepared by ball milling of pure elemental powders and subsequent hot-press sintering of powder mixture at 750 and 825 °C for 2 h. For comparison, this alloy was also prepared by induction melting technology and then homogenized at 850 °C for 24 h. Further, they were aged at 430 °C for 2 h. The microstructure, damping capacity and microhardness of the hot-press-sintered and induction-melted alloys have been investigated. The results show that the microstructure of the powder mixture upon ball milling mainly comprises convoluted composite particles containing α-Mn and γ-Cu phases, and isolated α-Mn ones around. The high compactness of the alloys is obtained after hot-press sintering (94.8 and 98.6% at 750 and 825 °C, respectively). At a holding temperature of 750 °C, the microstructure of the alloy is primarily composed of γ-MnCu, γ-CuMn and α-Mn grains. With increasing the target temperature to 825 °C, the single γ-MnCu solid solution has been formed in the alloy by diffusion of Mn etc. into γ-Cu lattices. The hot-press-sintered alloys (especially at 825 °C) possess relatively high damping capacity although which is still lower than that of induction-melted one. In contrast, the microhardness of the hot-press-sintered alloys (especially at 750 °C) is obviously higher than that of the induction-melted one.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Studies on electrochemical lithium insertion in isostructural titanium niobate and tantalate phases with shear ReO{sub 3} structure

Graphical abstract: - Highlights: • Electrochemical lithium insertion into ReO{sub 3} type phases TiNb{sub 2}O{sub 7}, TiTa{sub 2}O{sub 7} is feasible. • TiNb{sub 2}O{sub 7} exhibits good cycling behavior and high reversible capacity of 212 mAh g{sup −1}. • TiTa{sub 2}O{sub 7} exhibits reversible capacity of 100 mAh g{sup −1}. - Abstract: TiNb{sub 2}O{sub 7} and TiTa{sub 2}O{sub 7} phases are synthesized by solid-state reaction method and are investigated for electrochemical Li insertion/extraction. The electrochemical insertion of Li in these phases is characterized by both solid solution and two-phase regimes. The structure is stable toward Li insertion/extraction. The first cycle discharge capacity values are 307 mAh g{sup −1} and 215 mAh g{sup −1} in the voltage range of 3.0–1.0 V for TiNb{sub 2}O{sub 7} and TiTa{sub 2}O{sub 7} phases, respectively. The discharge capacities of TiNb{sub 2}O{sub 7} and TiTa{sub 2}O{sub 7} are 212 mAh g{sup −1} and 100 mAh g{sup −1}, respectively, after 20 cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Sn-enriched Ge/GeSn nanostructures grown by MBE on (001) GaAs and Si wafers

Elastically stressed metastable GeSn layers with a tin molar fraction as large as 0.185 are grown on (001) Si and GaAs wafers covered with a germanium buffer layer. A set of wafers with a deviation angle in the range 0°–10° is used. It is established that the GeSn crystal undergoes monoclinic deformation with the angle β to 88° in addition to tetragonal deformation. Misorientation of the wafers surface results in increasing efficiency of the incorporation of tin adatoms into the GeSn crystal lattice. Phase separation in the solid solution upon postgrowth annealing of the structures begins long before the termination of plastic relaxation of elastic heteroepitaxial stresses. Tin released as a result of GeSn decomposition predominantly tends to be found on the surface of the sample. Manifestations of the brittle–plastic mechanism of the relaxation of stresses resulting in the occurrence of microcracks in the subsurface region of the structures under investigation are found.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of alloying by lanthanum and high rhenium superalloys on the basis of Ni-Al-Cr on the structure and phase composition

This paper presents transmission and scanning electronic microscope investigations of Ni-Al-Cr superalloy alloyed with additional Re and La elements. This superalloy is obtained by the directional solidification method and subsequently is subjected to two-stage high-temperature annealing: 1) at T = 1150°C, the test time is 1 hour; 2) at T = 1100°C, the testing time is 1430 hours. It was found that the γ- and γ′-phases are the main phases in the two states on the basis of fcc lattice. Where γ is the disordered fcc solid solution and γ′-phase is the main phase with an ordered arrangement of atoms having the L1{sub 2} superstructure. It is shown that such additional elements as Re and La result in the formation of new phases in Ni-Al-Cr accompanied by considerable modifications of quasi-cuboid structure in its γ′-phase. The phase composition and morphology of the phases are studied.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The effect of Si on the microstructure and mechanical properties of spark plasma sintered boron carbide

Highlights: • Si addition leads to a dense final product at a low sintering temperature. • The added Si preferentially formed SiC and borosilicate glass instead of replacing the chain atoms in boron carbide. • The hardness of our Si-containing boron carbide is 30–35% greater than currently in-use commercial boron carbide plates. - Abstract: Fully dense boron carbide discs were achieved by spark plasma sintering boron carbide powders with 10 wt% silicon. The silicon did not diffuse into boron carbide grains to produce a solid solution of Si-doped boron carbide; instead the silicon reacted with impurities in the starting powder to form β-SiC and borosilicate glass. The resultant new phases facilitated densification of the multiphase ceramic through liquid phase-assisted sintering. The resultant material exhibits improved hardness (34.3 GPa Vikers hardness under 1 kg load) with toughness comparable to both Si-free and commercially available boron carbide.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nano-magnetism of magnetostriction in Fe{sub 35}Co{sub 65}

The nature of the large magnetostriction in body-centered Fe-based solid solutions has been widely discussed in the literature. Here, we use a combination of magnetostriction, magnetization, torque, and transmission electron microscopy measurements of specially annealed Co{sub 65}Fe{sub 35} to show that the magnetostriction is caused by coherent uniaxial nano-precipitates. We show further that these nano-precipitates lower the magnetocrystalline anisotropy in these alloys to K{sub 1} = −2.16 × 10{sup 4} J/m{sup 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effects of Tungsten Addition on the Microstructure and Mechanical Properties of Near-Eutectic AlCoCrFeNi{sub 2} High-Entropy Alloy

The effects of tungsten addition on the microstructure and mechanical properties of near-eutectic AlCoCrFeNi{sub 2} high-entropy alloy were investigated in this paper. The AlCoCrFeNi{sub 2}W{sub x} alloys comprised the primary BCC phase plus eutectic FCC/BCC phases. It was found that W element can both promote the formation of the primary BCC phase and act as a solid solution strengthening element. The hardness of the AlCoCrFeNi{sub 2}W{sub x} alloys increased from HV 293 to HV 356.2 with the increase in W content. The addition of W element improved the strength of alloys but reduced ductility. Thereinto, the AlCoCrFeNi{sub 2}W{sub 0.2} alloy showed the most excellent compressive properties with the fracture strength of 2785.9 MPa and the plastic strain of 0.42, respectively, which implied the potential industrial application values.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Ceramic planar waveguide structures for amplifiers and lasers

Ceramic and crystalline weakly guiding optical fibres with the core - cladding refractive index difference of 10{sup -2} - 10{sup -4} are fabricated by a hot pressing method. The waveguides with one or several cores for operation in the spectral range 0.2 - 5 {mu}m are produced. The waveguides are based on CaF{sub 2}, SrF{sub 2}, and BaF{sub 2} ceramics and crystals and their solid solutions doped with trivalent Pr, Nd, Tb, Dy, Yb, Ho, Er, and Tm ions, as well as on LiF ceramics and crystals with colour centres. The first results of investigation of the lasing properties of ceramic SrF{sub 2} : NdF waveguides under diode pumping are presented, and the prospects of further investigation are discussed. (lasers)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Nanocarbon-copper thin film as transparent electrode

Researchers seeking to enhance the properties of metals have long pursued incorporating carbon in the metallic host lattice in order to combine the strongly bonded electrons in the metal lattice that yield high ampacity and the free electrons available in carbon nanostructures that give rise to high conductivity. The incorporation of carbon nanostructures into the copper lattice has the potential to improve the current density of copper to meet the ever-increasing demands of nanoelectronic devices. We report on the structure and properties of carbon incorporated in concentrations up to 5 wt. % (∼22 at. %) into the crystal structure of copper. Carbon nanoparticles of 5 nm–200 nm in diameter in an interconnecting carbon matrix are formed within the bulk Cu samples. The carbon does not phase separate after subsequent melting and re-solidification despite the absence of a predicted solid solution at such concentrations in the C-Cu binary phase diagram. This material, so-called, Cu covetic, makes deposition of Cu films containing carbon with similar microstructure to the metal possible. Copper covetic films exhibit greater transparency, higher conductivity, and resistance to oxidation than pure copper films of the same thickness, making them a suitable choice for transparent conductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Milestone report: The simulation of radiation driven gas diffusion in UO 2 at low temperature

Below 1000 K it is thought that fission gas diffusion in nuclear fuel during irradiation occurs through atomic mixing due to radiation damage. This is an important process for nuclear reactor performance as it affects fission gas release, particularly from the periphery of the pellet where such temperatures are normal. Here we present a molecular dynamics study of Xe and Kr diffusion due to irradiation. Thermal spikes and cascades have been used to study the electronic stopping and ballistic phases of damage, respectively. Our results predict that O and Kr exhibit the greatest diffusivity and U the least, while Xe lies in between. It is concluded that the ballistic phase does not sufficiently account for the experimentally observed diffusion. Preliminary thermal spike calculations indicate that the electronic stopping phase generates greater fission gas displacement than the ballistic phase, although further calculation must be carried out to confirm this. A good description of the system by the empirical potentials is important over the very wide temperatures induced during thermal spike and damage cascade simulations. This has motivated the development of a parameter set for gas-actinide and gas-oxygen interactions that is complementary for use with a recent many-body potential set. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO 2 , ThO 2 , UO 2 and PuO 2 . These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matching to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT binding energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO 2 , ThO 2 , UO 2 and PuO 2 , providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO 2 as well as advanced MOX fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Phase transformations in a Cu−Cr alloy induced by high pressure torsion

Phase transformations induced by high pressure torsion (HPT) at room temperature in two samples of the Cu-0.86 at.% Cr alloy, pre-annealed at 550 °C and 1000 °C, were studied in order to obtain two different initial states for the HPT procedure. Observation of microstructure of the samples before HPT revealed that the sample annealed at 550 °C contained two types of Cr precipitates in the Cu matrix: large particles (size about 500 nm) and small ones (size about 70 nm). The sample annealed at 1000 °C showed only a little fraction of Cr precipitates (size about 2 μm). The subsequent HPT process resulted in the partial dissolution of Cr precipitates in the first sample and dissolution of Cr precipitates with simultaneous decomposition of the supersaturated solid solution in another. However, the resulting microstructure of the samples after HPT was very similar from the standpoint of grain size, phase composition, texture analysis and hardness measurements. - Highlights: • Cu−Cr alloy with two different initial states was deformed by HPT. • Phase transformations in the deformed materials were studied. • SEM, TEM and X-ray diffraction techniques were used for microstructure analysis. • HPT leads to formation the same microstructure independent of the initial state.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Formation of titanium carbonitride film by laser treatment: Structural and transport properties

In-plane and Out-of-plane Grazing incidence X-ray diffraction is used to characterize the preferred orientation present in the titanium carbonitride films using ADXRD beamline at INDUS 2 synchrotron radiation source. GIXRD shows the formation of mixture of FCCTiC{sub x}N{sub (1-x)} films for different values of x along with the solid solution. From the in-plane and out-of-plane XRD measurements, we have observed that a specific texture along the c-axis of Ti has been formed during the laser treatment process. Due to the diffusion of C and N into Ti, the resistance of the specimen has been decreases with respect to the resistance of pure Ti sheet. The formed phases are stable and there is no structural relaxation has been observed during annealing process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Examination of the Capabilities of Metalorganic Vapor-Phase Epitaxy in Fabrication of Thin InAs/GaSb Layers

The capabilities of metalorganic vapor-phase epitaxy (MOVPE) in fabrication of structures with thin (1–2 nm) alternating InAs/GaSb layers on a GaSb substrate are studied. The characteristics of these structures were examined using transmission electron microscopy and methods of photo- and electroluminescence. It was found that two GaInAsSb solid solutions of different compositions were formed in the active regions of structures in the given growth conditions. The fabricated system was characterized by an emission wavelength of 4.96 μm at a temperature of 77 K. The results reveal new opportunities for bandgap engineering of semiconductor structures based on InAs/GaSb, which are designed for optoelectronic devices operating in the infrared range, provided by MOVPE.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Degradation processes of reinforced concretes by combined sulfate–phosphate attack

A novel form of alteration due to the interaction between hydrated cement phases and sulfate and phosphate-based pollutants is described, through the characterization of concrete samples from an industrial reinforced concrete building. Decalcification of the cement matrices was observed, with secondary sulfate and phosphate-based mineral formation, according to a marked mineralogical and textural zoning. Five alteration layers may be detected: the two outermost layers are characterized by the presence of gypsum–brushite solid solution phases associated with anhydrous calcium sulfates and phosphates, respectively, while a progressive increase in apatite and ammonium magnesium phosphates is observable in the three innermost layers, associated with specific apatite precursors (brushite, octacalcium phosphate and amorphous calcium phosphate, respectively). The heterogeneous microstructural development of secondary phases is related to the chemical, pH and thermal gradients in the attacked cementitious systems, caused by different sources of pollutants and the exposure to the sun's radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A new member of “114” family Ca{sub 1−x}Eu{sub x}BaZn{sub 2+x}Ga{sub 2−x}O{sub 7} (x≤0.24): Structure and luminescence

New “114” oxides Ca{sub 1−x}Eu{sub x}BaZn{sub 2+x}Ga{sub 2−x}O{sub 7} (x≤0.24) were synthesized by solid state reaction. Rietveld refinements were performed on high quality powder XRD data in the space group P6{sub 3}mc. Zn{sup 2+} and Ga{sup 3+} co-occupy T1 and T2 positions, which are both in tetrahedral coordinated environment. Comparing the host compound, O3 moves towards T2 cation as much as 0.08 Å when x=0.24. It is the most observable structural change during the substitution. By comparing the structures of CaBaZn{sub 2}Ga{sub 2}O{sub 7} (P6{sub 3}mc) and CaBaCo{sub 4}O{sub 7} (Pbn2{sub 1}), we find that smaller cations in tetrahedral sites would lead to a lower symmetry in “114” oxides. Luminescent spectra show the noncentrosymmetric coordination of Eu{sup 3+}, and the f–f excitations are comparable to CT-excitation. No concentration quenching was observed up to x=0.24. The optical band gaps were estimated to be 3.8 eV for Ca{sub 1−x}Eu{sub x}BaZn{sub 2+x}Ga{sub 2−x}O{sub 7} (x=0, 0.16). - Graphical abstract: Reitveld refinements show Ca{sub 1−x}Eu{sub x}BaZn{sub 2+x}Ga{sub 2−x}O{sub 7} all crystallize in P6{sub 3}mc. By Eu{sup 3+}-doping, O3 show the most obvious movement (∼0.08 Å) along the c-axis. Display Omitted - Highlights: • Ca{sub 1−x}Eu{sub x}BaZn{sub 2+x}Ga{sub 2−x}O{sub 7} (x≤0.24) solid solutions were synthesized in air. • Rietveld refinements of high quality powder XRD show good convergences. • Ca{sub 1−x}Eu{sub x}BaZn{sub 2+x}Ga{sub 2−x}O{sub 7} all crystallize in the space group P6{sub 3}mc. • Luminescent spectra of Eu{sup 3+} show no quenching effect up to x=0.24. • Optical band gaps for CaBaZn{sub 2}Ga{sub 2}O{sub 7} are estimated to be 3.8 eV.

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

Strength Variation in Processing Multiport Extrusion Tubes of A1100 and A3102 Alloys

The manufacturing process of multiport extrusion tubes generally includes homogenization, extrusion, roll leveling and heat treatment. In order to investigate the influence of the manufacturing procedures on strength variation of multiport extrusion tubes made of A1100 and A3102 alloys, the tube fabrication experiments and following materials characterization are carried out. The alloys’ stress–strain curves after every processing procedure are measured, and pressure-bearing capacity of the tubes is tested. The tubes’ strength and pressure-bearing capacity reach the peak values after straightening process and drop to the minimum after annealing. The contributions of solid solution hardening, grain boundary hardening and constituent particle strengthening to yield strength are evaluated. It is deduced that cluster hardening is the dominant strengthening mechanism for the as-homogenized and as-extruded samples; the contribution of clusters is second to work hardening after straightening process; slight cold work in conjunction with high-temperature annealing accelerates abnormal grain growth. The loss of strength increment from clusters can be interpreted by the remarkable reduction of high-angle grain boundaries after abnormal grain growth.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Thermoelectric properties in the series Ti{sub 1-x}Ta{sub x}S{sub 2}

Polycrystalline samples in the series Ti{sub 1-x}Ta{sub x}S{sub 2} with x varying from 0 to 1 were prepared using solid-liquid-vapor reaction and spark plasma sintering. Rietveld refinements of X-ray diffraction data are consistent with the existence of a full solid solution for x ≤ 0.4. Transport measurements reveal that tantalum can act as electron donor when substituted in the Ti sites. As a consequence, the electrical resistivity and the absolute value of the Seebeck coefficient decrease with Ta content due to an increase in the carrier concentration. The lattice thermal conductivity being reduced due to mass fluctuation effect, the ZT values in Ti{sub 0.95}Ta{sub 0.05}S{sub 2} is slightly increased as compared to TiS{sub 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Laser Irradiation on the PTCR Behavior of Semiconducting Barium Strontium Titanate Ceramics

This paper examines the effect of pulsed laser irradiation on the electrical properties of n-type semiconductor ferroelectric ceramics (based on a (Ba,Sr)TiO{sub 3} solid solution) with a planar contact configuration. The elemental compositions and surface morphologies of the material before and after laser irradiation are compared using scanning electron microscopy data. In the framework of the well-known Heywang model for the positive temperature coefficient of resistance effect, we calculate the resistance of the material as a function of temperature for the paraelectric phase and determine parameters of grain boundaries that ensure good agreement between the experimental data and theoretical curves.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗