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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

The microstructure and He + ion irradiation behavior of novel low-activation W-Ta-Cr-V refractory high entropy alloy for nuclear applications

Microstructure and nanohardness of a nearly equimolar W-Ta-Cr-V high entropy alloy (HEA), as well as its irradiation response under He + irradiation, were investigated. The single-phase body-centered cubic nanostructured alloy with a 1 µm thick layer was fabricated on a silicon substrate using a magnetron sputtering method. The HEA film has a complex microstructure consisting of micrometric domains that exhibit internal nanostructure controlled by their crystal orientation. The measured nanohardness of the W-Ta-Cr-V alloy is 13 ± 2 GPa, which significantly exceeds the hardness of nanocrystalline tungsten as a result of the high solid-solution strengthening effect. In order to evaluate the irradiation resistance of the HEA film, the material was irradiated with 200 keV He + ions at room temperature, with two different ion fluences: 1 × 10 16 and 5 × 10 16 ions/cm 2 . Using transmission electron microscopy, a high density of extremely fine He bubbles is observed that were uniformly distributed in the matrix. The increase of He + ion fluence increased the density of bubbles, whereas their size remained at a similar level, which indicates that the damage proceeds by the nucleation of additional He bubbles, not by their growth.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Recent progress on understanding the temperature-dependent irradiation resistance ranking among NiFe, NiCoCr, and NiCoFeCr alloys: A review

Systematic temperature-effects investigations on damage evolution in ion-irradiated Ni-based concentrated solid-solution alloys (CSAs) are pivotal to provide reliance on their use in nuclear applications. Here, in search of the origin behind the temperature-dependent irradiation resistance ranking among equiatomic NiFe, NiCoCr and NiCoFeCr alloys, we have compared, previously experimental and theoretical published data involving ion irradiation experiments performed on these alloys with new ion channeling results from ion-irradiated NiCoFeCr at 500 K. Moreover, the current results are compared with independent theoretical calculations and relevant TEM results from literature, which allow us to suggest that the lower migration energy of vacancies in NiCoCr, as compared with those in NiFe and NiCoFeCr, is the reason behind why NiCoCr is no longer outperforming NiFe under ion irradiation above 300 K.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2018

Fabrication of 7075-0.25Sc-0.15Zr Alloy with Excellent Damping and Mechanical Properties by FSP and T6 Treatment

This study investigated the effects of Sc and Zr additions, friction stir processing (FSP), and subsequent solid solution and artificial aging (T6) treatment on the microstructure, damping capacity, and mechanical properties of 7075 Al alloy. The minor Sc and Zr additions promoted the grain refinement of this alloy during FSP and inhibited the growth of fine equiaxed grains in the FSP sample during subsequent T6 treatment. Thus, the fine equiaxed grain structure and high density of the η′ precipitated phase were simultaneously obtained in the 7075 Al alloy containing Sc and Zr after FSP and T6 treatment, and this sample exhibited superior mechanical properties and damping capacity to those of the 7075 Al alloy after T6 treatment. This work provides an effective strategy for preparing Al alloys with excellent damping capacity and mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced strength and ductility of a tungsten-doped CoCrNi medium-entropy alloy

Developing metallic materials with a good combination of strength and ductility has been an unending pursuit of materials scientists. The emergence of high/medium-entropy alloys (HEA/MEA) provided a novel strategy to achieve this. In this work, we also strengthened a strong-and-ductile MEA using a traditional solid solution strengthening theory. The selection of solute elements was assisted by mechanical property and microstructure predictive models. Extensive microstructural characterizations and mechanical tests were performed to verify the models and to understand the mechanical behavior and deformation mechanisms of the designated CoCrNi–3W alloy. Our results show good experiment-model agreement. The incorporation of 3 at.% W into the ternary CoCrNi matrix increased its intrinsic strength by ~20%. External strengthening through microstructural refinement led to a yield strength nearly double that of the parent alloy, CoCrNi. The increase in strength is obtained with still good ductility when tested down to 77 K. Nanoscale twin boundaries are observed in the post-fracture microstructure under 77 K. Finally, the combination of strength and ductility after W additions deviate from the traditional strength-ductility-trade-off contour.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment

Highlights: • The formation and spheroidization of the eutectic-like carbides are found in the Hastelloy N alloy during welding and PWHT. • All precipitates in the joints before and after the PWHT are identified as a M{sub 6}C type carbide with different morphology. • The diffusion of main element of Mo leads to the decrease of lattice parameter of the carbide during the welding and PWHT. - Abstract: The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M{sub 6}C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M{sub 6}C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M{sub 6}C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M{sub 6}C carbides, which results in a decrease of the lattice parameter.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High energy storage density of temperature-stable X9R ceramics

Highlights: • The addition of KNbO{sub 3} improved the temperature-stable properties and energy density. • The x = 0.07 and x = 0.09 sample met the X8R requirements. • The x = 0.03 and x = 0.05 sample met the X9R requirements. • The maximum discharge energy density of x = 0.05 sample reached up to 2 J/cm{sup 3} at 17.85 kV/mm. - Abstract: The effects of KNbO{sub 3} addition on the temperature stability of dielectric properties and energy-storage performances of Sr{sub 0.5}Na{sub 0.25}Bi{sub 0.25}TiO{sub 3}-MgO ((1-x)SNBTM5-xKN) ceramics were systematically investigated. It shows that KNbO{sub 3} has completely diffused into SNBT lattice to form a solid solutions. Two obvious maxima in permittivity curves were observed due to the formation of the polar nanoregions. For the sample with x = 0.05 addition, its permittivity variation region, where △ε'/ε'{sub 25 °C} is no more than ± 15%, retains wide the range from −55 °C to 200 °C, indicating that the ceramics can meet the requirement of X9R specification. Furthermore, this sample shows a high electric breakdown strength of 17.85 kV/mm and a high discharge energy density of 2 J/cm{sup 3}. The noticeable reduced remnant polarization induced by KNbO{sub 3} addition also contributes to the improved energy-storage performances. Thus, these novel ceramics with the aforementioned characteristics will potentially benefit the applications of high pulse power capacitors at high temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Local spring effect in titanium-based layered oxides

Titanium-based layered oxides (TLOs) are one of the most promising electrode material families for sodium-ion batteries (NIBs) due to their smooth charge/discharge profiles and excellent cycle performance. However, the reaction mechanism of these materials, especially the reason for the disappearance of multiple voltage plateaus, is still not clear. Herein, two representative TLOs (Na 2/3 Ni 1/3 Ti 2/3 O 2 and Na 2/3 Co 1/3 Ti 2/3 O 2 ) with the same P2 crystal structure have been studied to scrutinize those unexplained issues. In situ synchrotron high-energy X-ray diffraction revealed a solid solution reaction mechanism for both, suggesting the absence of rigid phase transitions upon electrochemical cycling. An interesting “spring effect” of the TiO 6 octahedron, i.e., the reversible vibration of the central Ti atom inside the local octahedron upon electrochemical redox, was demonstrated by advanced X-ray absorption spectroscopy and theoretical calculations. Such an effect could suppress the rigid phase transitions, and result in smooth charge/discharge profiles and enhanced cycle stability. Finally, this work not only accounts for the disappearance of multiple voltage plateaus of TLOs for NIBs, but also provides an effective local-structure viewpoint to increase the cycle stability of electrode materials for other advanced battery systems.

25 ENERGY STORAGE↗
DOE OSTI2014

Electronic structure of ruthenium-doped iron chalcogenides

The structural and electronic properties of hypothetical Ru{sub x}Fe{sub 1−x}Se and Ru{sub x}Fe{sub 1−x}Te systems have been investigated from first principles within the density functional theory (DFT). Reasonable values of lattice parameters and chalcogen atomic positions in the tetragonal unit cell of iron chalcogenides have been obtained with the use of norm-conserving pseudopotentials. The well known discrepancies between experimental data and DFT-calculated results for structural parameters of iron chalcogenides are related to the semicore atomic states which were frozen in the used here approach. Such an approach yields valid results of the electronic structures of the investigated compounds. The Ru-based chalcogenides exhibit the same topology of the Fermi surface (FS) as that of FeSe, differing only in subtle FS nesting features. Our calculations predict that the ground states of RuSe and RuTe are nonmagnetic, whereas those of the solid solutions Ru{sub x}Fe{sub 1−x}Se and Ru{sub x}Fe{sub 1−x}Te become the single- and double-stripe antiferromagnetic, respectively. However, the calculated stabilization energy values are comparable for each system. The phase transitions between these magnetic arrangements may be induced by slight changes of the chalcogen atom positions and the lattice parameters a in the unit cell of iron selenides and tellurides. Since the superconductivity in iron chalcogenides is believed to be mediated by the spin fluctuations in single-stripe magnetic phase, the Ru{sub x}Fe{sub 1−x}Se and Ru{sub x}Fe{sub 1−x}Te systems are good candidates for new superconducting iron-based materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

The influence of the concentration of Sr ions on the crystal and magnetic structures of Ba{sub 2} –{sub x}Sr{sub x}FeMoO{sub 6} double perovskites (x = 0–1.6)

The crystal and magnetic structures of a solid solution of double perovskite Ba{sub 2–} {sub x}Sr{sub x}FeMoO{sub 6} (x = 0–1.6) have been investigated by neutron diffraction. The high-resolution diffraction patterns have provided precise information about the changes in the crystal and magnetic structures with an increase in the strontium content and data on the behavior of the sample microstructure. Replacement of barium with strontium leads to a change in the lattice symmetry from cubic (x = 0, sp. gr. Fm3̄m)) to tetragonal (x = 0.4, sp. gr. I4/m). At x = 1.0, the symmetry is either tetragonal (sp. gr. I4/m) or orthorhombic (sp. gr. Fmmm), and at x = 1.6 the symmetry becomes again tetragonal (sp. gr. I4/m). The values of the Curie temperature and microstrain increase with an increase in the strontium content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate

Laser-clad composite coatings on the Ti6Al4V substrate were heat-treated at 700, 800, and 900 °C for 1 h. The effects of post-heat treatment on the microstructure, microhardness, and fracture toughness of the coatings were investigated by scanning electron microscopy, X-ray diffractometry, energy dispersive spectroscopy, and optical microscopy. The wear resistance of the coatings was evaluated under dry reciprocating sliding friction at room temperature. The coatings mainly comprised some coarse gray blocky (W,Ti)C particles accompanied by the fine white WC particles, a large number of black TiC cellular/dendrites, and the matrix composed of NiTi and Ni{sub 3}Ti; some unknown rich Ni- and Ti-rich particles with sizes ranging from 10 nm to 50 nm were precipitated and uniformly distributed in the Ni{sub 3}Ti phase to form a thin granular layer after heat treatment at 700 °C. The granular layer spread from the edge toward the center of the Ni{sub 3}Ti phase with increasing temperature. A large number of fine equiaxed Cr{sub 23}C{sub 6} particles with 0.2–0.5 μm sizes were observed around the edges of the NiTi supersaturated solid solution when the temperature was further increased to 900 °C. The microhardness and fracture toughness of the coatings were improved with increased temperature due to the dispersion-strengthening effect of the precipitates. Dominant wear mechanisms for all the coatings included abrasive and delamination wear. The post-heat treatment not only reduced wear volume and friction coefficient, but also decreased cracking susceptibility during sliding friction. Comparatively speaking, the heat-treated coating at 900 °C presented the most excellent wear resistance. - Highlights: • TiC + WC reinforced intermetallic compound matrix composite coatings were produced. • The formation mechanism of the reinforcements was analyzed. • Two precipitates were generated at elevated temperature. • Cracking susceptibility and microhardness of the coatings were improved. • Post-heat treatment enhances wear resistance of the coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A New Radionuclide Sorption Database for Cementitious Materials Accounting for Geochemical Evolution - 18477

Cementitious materials are being widely used as solidification/stabilisation and barrier materials for a variety of radioactive wastes, due to their favourable retention properties for metals and radionuclides. The retention properties result from mineral phases in hydrated cement that (i) possess a high density and diversity of reactive sites for the fixation of radionuclides through a variety of sorption reactions, ranging from surface adsorption to incorporation and solid-solution formation, and (ii) buffer pH in the range 10- 13, depending on composition, which tends to limit the solubility of many metal ions. A quantitative database on the solid/liquid distribution behaviour ('sorption database') of 25 elements (Ag, Am, Be, C, Ca, Cl, Cs, H, I, Mo, Nb, Ni, Np, Pa, Pb, Pd, Pu, Ra, Se, Sn, Sr, Tc, Th, U, Zr) in hydrated cement systems is established on the basis of a consistent review and re-evaluation of literature data. Effects of geochemical evolution or ageing cements on sorption/incorporation processes are explicitly evaluated and quantified. In addition to recommended values, all underlying original experimental data and key experimental information are provided, which allows users to trace the given recommendations or to develop their own set of key values. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

Metamorphic Ga{sub 0.76}In{sub 0.24}As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In{sub 0.24}Al{sub 0.76}As/p-In{sub 0.24}Ga{sub 0.76}As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 10{sup 18} cm{sup –3} and completely remove the potential barrier, thereby reducing the series resistance of the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Preparation, crystal structure and enhanced bipolar response of 0.90BLNT-0.10BCT lead-free piezoceramics

In the present work, a solid solution of lead free 0.90[(Bi{sub 0.96}La{sub 0.04}){sub 0.5}Na{sub 0.5}TiO{sub 3}]-0.10(Ba{sub 0.90}Ca{sub 0.10}TiO{sub 3}] (abbreviated as 0.90BLNT-0.10BCT) piezoceramics has been synthesized by semi-wet technique. X-ray diffraction pattern confirms the phase formation. Rietveld refinement of XRD data demonstrates the coexistence of rhombhohedral (R3c) + tetragonal (P4mm) phase at room temperature. Raman spectrum is also support the above analysis. A large enhancement in bipolar strain of 0.12 % and calculated normalized strain, d*{sub 33} (defined as S{sub max}/E{sub max}) ~ 265 pm/V at 40kV/cm has been observed for this composition as compared to pure BLNT specimen, which make possible it as a potential lead-free candidates for piezoelectric applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Reaction Behaviors of Al-Killed Medium-Manganese Steel with Glazed MgO Refractory

In order to understand the reaction mechanism of Al-killed medium-Mn steel with glazed MgO refractory, some laboratory experiments were conducted at [1873 K (1600 °C)]. The refractory rods were glazed by four different basicity slags, and inserted into liquid steel (Mn:5.5 mass pct) for different times. The results show that MgO refractory can react with medium-Mn steel to generate (Mn, Mg)O solid solution with even (Mn, Mg)O-Al{sub 2}O{sub 3} spinel at the boundary of the refractory. When a glaze layer is formed at the edge of a MgO refractory, the glaze layer will supply inclusions into liquid steel and may act as a protection layer for the refractory. Although the glaze could also react with dissolved Mn in steel to generate MnO in both the glaze and refractory, the MnO contents in both the glaze and refractory are evidently lower than that without glaze. The reaction between glazed MgO refractory and liquid steel is influenced by the basicity of the glaze layer. High-basicity slag would hinder the generation of MnO in both the glaze and refractory. Therefore, lower-basicity glaze needs to be avoided for the steelmaking process of medium-Mn steel grades.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Fabrication and characterization of microstructure of stainless steel matrix composites containing up to 25 vol% NbC

AISI 440 stainless steels reinforced with various volume fractions of niobium carbide (NbC) particles of up to 25 vol% were fabricated in-situ using an argon arc furnace and then heat-treated to produce a martensitic matrix. Optical and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electron back-scatter diffraction (EBSD) techniques were used to analyze the microstructure, phases and composition of these composites. Interestingly, it was found that Chinese-script NbC could nucleate on existing primary NbC particles creating NbC clusters with complex microstructures. Additionally, hardness tests were used to evaluate viability in mining and mineral processing applications. The increase in NbC content resulted in an overall increase in the hardness of the composites while causing a marginal decrease in the amount of Cr in solid solution with the matrix, which could be a concern for corrosion resistance. The latter was due to the fact that the NbC lattice could dissolve a minor amount of Cr. Thermodynamic simulations also attributed this to a slight increase in M{sub 7}C{sub 3} precipitation. Nonetheless, these novel composites show great promise for applications in wear and corrosive environments. - Highlights: •Stainless steels reinforced with NbC particles of up to 25 vol% were fabricated. •NbC was formed in-situ in the steels using an arc melter. •Martensitic transformation of the matrix of each sample was achieved. •NbC reinforcements increased the bulk hardness values of the steels. •Dissolved Cr in the matrix of each sample was sufficient for passivity in theory.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Effect of Ion Irradiation on Nanocrystallization and Surface Relief of a Ribbon from Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} Alloy

Using the methods of X-ray diffraction and atomic force microscopy, the process of crystallization of an amorphous Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} alloy irradiated with accelerated Ar{sup +} ions is investigated. It is found out that an irradiation by the Ar{sup +} ions with the energy 30 keV at the ion current density 300 μA/cm{sup 2} (fluence 3.75·10{sup 15} cm{sup –2}, irradiation time ~2 s, ion-beam short-duration heating up to 350°С, which is 150°С lower than the thermal crystallization threshold) results in a complete crystallization of this amorphous alloy (throughout the bulk of a 25 μm ribbon) followed by precipitation of solid solution crystals of α-Fe(Si), close in its composition to Fe{sub 80}Si{sub 20}, stable phase of Fe{sub 3}Si, and metastable hexagonal phases. By the methods of atomic force and scanning tunneling microscopy it is shown that nanocrystallization caused by ion irradiation is accompanied by surface relief changes both on the irradiated and unirradiated sides of the Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} alloy ribbon at the depth exceeding by a factor of 10{sup 3} that of the physical ion penetration for this material. The data obtained, taking into account a significant temperature decrease and multiple acceleration of the crystallization process, serve an evidence of the radiation-dynamic influence of accelerated ions on the metastable amorphous medium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Superposition of M{sub 5}X{sub 5} superstructures and X-ray diffraction in TiO{sub 1.0} titanium monoxide

The interpretation of diffraction spectra of ordered high-temperature phases of solid solutions and strongly nonstoichiometric compounds is discussed. It has been shown that variations of the intensities of superstructure reflections, which cannot be explained within simple ordering models, can be due to the superposition of superstructures with different symmetries in the matrix of the basis crystal structure. Using an example of atom–vacancy ordering in TiO{sub 1.0} titanium monoxide, a model of the order–order transition state formed by the superposition of low-temperature monoclinic (space group A2/m (C2/m)) and high-temperature cubic (space group Pm3̅m) M{sub 5}X{sub 5} superstructures has been proposed. It has been shown that the transition state is thermodynamically equilibrium and should be implemented instead of the M{sub 5}X{sub 5} cubic superstructure. The transition state model can be considered as an M{sub (5–i)}X{sub (5–i)} superstructure (i = 1, 14/18, 11/18) with the monoclinic symmetry (space group P1m1).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thermal Expansion and Luminescent Properties of Triorthogermanates CaLa{sub 2-x}Eu{sub x}Ge{sub 3}O{sub 10} (x = 0.0–0.6)

Solid solutions CaLa{sub 2-x}Eu{sub x}Ge{sub 3}O{sub 10} (x = 0.0–0.6, Δx = 0.1) have been synthesized for the first time. The compounds are isostructural to CaLa{sub 2}Ge{sub 3}O{sub 10}, they crystallize in the monoclinic system, space group P2{sub 1}/c, Z = 4. The low-temperature X-ray diffraction studies have revealed the strain anisotropy of germanate CaLa{sub 2}Ge{sub 3}O{sub 10} crystal lattice in the temperature range 80–298 K, and the linear thermal expansion coefficients have been calculated. The optical properties of the activated phases have been studied, and the influence of the dopant concentration and the excitation wavelength on the luminescence characteristics of the synthesized compounds has been established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗