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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Influence of Ag doping concentration on structural and optical properties of CdS thin film

This work shows the influence of Ag concentration on structural properties of pulsed laser deposited nanocrystalline CdS thin film. X-ray photoelectron spectroscopy (XPS) studies confirm the dopant concentration in CdS films and atomic concentration of elements. XPS studies show that the samples are slightly sulfur deficient. GAXRD scan reveals the structural phase transformation from cubic to hexagonal phase of CdS without appearance of any phase of CdO, Ag{sub 2}O or Ag{sub 2}S suggesting the substitutional doping of Ag ions. Photoluminescence studies illustrate that emission intensity increases with increase in dopant concentration upto 5% and then decreases for higher dopant concentration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Phase evolution during conventional and reactive flash sintering of (Mg,Ni,Co,Cu,Zn)O via in situ X-ray diffraction

Reactive flash sintering (RFS) enables the simultaneous synthesis and sintering of ceramics and has been shown to affect the reaction pathway of different materials. Herein, in situ synchrotron X-ray diffraction (XRD) is used to investigate the (Mg,Ni,Co,Cu,Zn)O entropy-stabilized oxide formation during: (i) conventional heating and (ii) RFS under current rate-controlled mode. The same reaction pathway is verified in both instances: the starting rock-salt (RS), spinel (Co 3 O 4 ), tenorite (CuO), and wurtzite (ZnO) phases transform into a single RS phase with a (1 1 1) to (2 0 0) intensity ratio of 0.67, consistent with a random distribution of the cations into the structure. Pt lattice peak shift from the XRD patterns is used as standard to monitor the sample surface temperature, revealing a strong endothermic reaction during the RS single-phase formation (Pt peaks shift toward higher angles while increasing sample temperature/current density). Furthermore, in RFS, the single-phase RS structure is formed in just 60 s at a furnace temperature of 600°C and a current rate of 220 mA mm -2 /min. Therefore, RFS greatly accelerates the synthesis of (Mg,Ni,Co,Cu,Zn)O, however, it does not play a role in the reaction pathway for this material formation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Friction Stir Processing for Efficient Manufacturing

Friction at contacting surfaces in relative motion is a major source of parasitic energy loss in machine systems and manufacturing processes. Consequently, friction reduction usually translates to efficiency gain and reduction in energy consumption. Furthermore, friction at surfaces eventually leads to wear and failure of the components thereby compromising reliability and durability. In order to reduce friction and wear in tribological components, material surfaces are often hardened by a variety of methods, including conventional heat treatment, laser surface hardening, and thin-film coatings. While these surface treatments are effective when used in conjunction with lubrication to prevent failure, they are all energy intensive and could potentially add significant cost. A new concept for surface hardening of metallic materials and components is Friction Stir Processing (FSP). Compared to the current surface hardening technologies, FSP is more energy efficient has no emission or waste by products and may result in better tribological performance. FSP involves plunging a rotating tool to a predetermined depth (case layer thickness) and translating the FSP tool along the area to be processed. This action of the tool produces heating and severe plastic deformation of the processed area. For steel the temperature is high enough to cause phase transformation, ultimately forming hard martensitic phase. Indeed, FSP has been used for surface modification of several metals and alloys so as to homogenize the microstructure and refine the grain size, both of which led to improved fatigue and corrosion resistance. Based on the effect of FSP on near-surface layer material, it was expected to have beneficial effects on friction and wear performance of metallic materials. However, little or no knowledge existed on the impact of FSP concerning friction and wear performance the subject of the this project and final report. Specifically for steel, which is the most dominant tribological material, FSP can replace the current conventional surface hardening techniques used for friction and wear performance. Friction Stir Link Inc. (FSL) is teamed with Argonne National Laboratory (ANL) to develop and optimize FSP for friction and wear performance enhancement. The ultimate goal is to offer FSP and an effective alternative to some of the current energy intensive and high-cost surface hardening processes.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2011

An Experimental Exploration of Chemical Bond Characteristic Bulk Modulus and Phase Stability in ZnO: Cu Nanocrystals under High Pressure

The high pressure induced phase transitions in Zn{sub 1-x} Cu{sub x} O (x = 0.005 and 0.011) are investigated by angle-dispersive synchrotron radiation X-ray diffraction. As the pressure increases, phase transformations from the wurtzite structure to the rocksalt structure are observed in both samples, with the transition pressures at 9.8 GPa and 7.9 GPa, respectively. With the increasing of the Cu-doping concentration in ZnO, crystalline parameters, the bulk moduli, and the Zn-O bond lengths all increased, meanwhile, the transition pressures decreased. The results could be explained in terms of the reduction of phase transformation barriers and the lowering of bond energy.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microstructure, Texture, and Strength Development during High-Pressure Torsion of CrMnFeCoNi High-Entropy Alloy

The equiatomic face-centered cubic high-entropy alloy CrMnFeCoNi was severely deformed at room and liquid nitrogen temperature by high-pressure torsion up to shear strains of about 170. Its microstructure was analyzed by X-ray line profile analysis and transmission electron microscopy and its texture by X-ray microdiffraction. Microhardness measurements, after severe plastic deformation, were done at room temperature. It is shown that at a shear strain of about 20, a steady state grain size of 24 nm, and a dislocation density of the order of 1016 m−2 is reached. The dislocations are mainly screw-type with low dipole character. Mechanical twinning at room temperature is replaced by a martensitic phase transformation at 77 K. The texture developed at room temperature is typical for sheared face-centered cubic nanocrystalline metals, but it is extremely weak and becomes almost random after high-pressure torsion at 77 K. The strength of the nanocrystalline material produced by high-pressure torsion at 77 K is lower than that produced at room temperature. The results are discussed in terms of different mechanisms of deformation, including dislocation generation and propagation, twinning, grain boundary sliding, and phase transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

On the high-temperature stability of the Al 8 Cu 3 Ce intermetallic in an additively manufactured Al-Cu-Ce-Zr alloy

High-temperature resistant eutectic Al alloys are crucial materials for lightweight and energy efficient design in the automotive and aviation industries. Additive manufacturing offers a pathway to refine eutectic microstructures and develop novel alloys with superior high-temperature strength. High-volume fraction intermetallic Al-Cu-Ce alloys have been developed to deliver high-temperature strength in combination with reduced hot-tearing susceptibility. Zr is added to provide additional strengthening via nanoscale Al 3 Zr precipitation, and to stabilize and avoid coarsening of the Al 8 Cu 3 Ce phase. However, the detailed interaction between Zr and Al 8 Cu 3 Ce remains unexplored. In this work, we show with synchrotron X-ray diffraction that laser powder bed fusion fabricated Al-Cu-Ce and Al-Cu-Ce-Zr alloys contain predominantly the Al 8 Cu 3 Ce intermetallic in the as-fabricated condition. Heat treatment of the Al-Cu-Ce alloy results in the Al 8 Cu 3 Ce → Al 8 Cu 4 Ce phase transformation. In the Al-Cu-Ce-Zr alloy, minor fractions of (Al,Cu,Si) 4 Ce and Al 2 Cu-θ are found in the as-fabricated condition, while Al 8 Cu 3 Ce remains stable during heat treatment. Atom probe microscopy quantifies intermetallic stoichiometries and reveals how Zr is enriched at the Al-matrix/Al 8 Cu 3 Ce interface acting as a diffusion barrier against solute exchange. Calibrated thermodynamic modeling underpins this as a kinetic effect. Here, a qualitative microstructural model summarizes, how Zr stabilizes Al 8 Cu 3 Ce against phase transformations and coarsening.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effective Lanthanide Diffusivity through U-Zr Metallic Fuel

Fuel-cladding chemical interaction (FCCI) is one of the main concerns for the performance of U-Zr metallic fuels. Although FCCI results in complex phase transformations and morphological changes in both the fuel and cladding sides of the interface, the formation of a brittle layer in the cladding side of the interface (sometimes referred to as wastage) has one of the most significant impacts on the cladding mechanical integrity. This brittle layer is associated with the formation of intermetallic compounds between the cladding constituents Fe, Cr and the lanthanide fission product species. The formation of this cladding wastage layer has been the focus of recent efforts to develop a mechanistic modeling framework, including production of lanthanides in the fuel, transport through the fuel to the fuel-cladding interface, and phase transformation to form intermetallic phases. To calculate the rate of transport of lanthanides through the fuel, a multi-scale computational approach has been used. Atomistic calculations have been performed to determine the diffusivities of Nd, the most prevalent lanthanide species, through the solid fuel matrix and along pore surfaces. These diffusivities have been used as input parameters for a mesoscale model to determine an effective diffusion coefficient that accounts for the formation of porosity, its interconnection, and infiltration with bond sodium from the fuel-cladding gap. The effective diffusivity has been used in engineering-scale simulations using the BISON fuel performance code, and BISON simulations have been compared to representative validation cases from the EBR-II reactor.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Redox Chemistry of the Subphases of α-CsPbI2Br and β-CsPbI2Br: Theory Reveals New Potential for Photostability

The logic in the design of a halide-mixed APb(I 1-x Br x ) 3 perovskite is quite straightforward: to combine the superior photovoltaic qualities of iodine-based perovskites with the increased stability of bromine-based perovskites. However, even small amounts of Br doped into the iodine-based materials leads to some instability. In the present report, using first-principles computations, we analyzed a wide variety of α-CsPbI 2 Br and β-CsPbI 2 Br phases, compared their mixing enthalpies, explored their oxidative properties, and calculated their hole-coupled and hole-free charged Frenkel defect (CFD) formations by considering all possible channels of oxidation. Nanoinclusions of bromine-rich phases in α-CsPbI 2 Br were shown to destabilize the material by inducing lattice strain, making it more susceptible to oxidation. The uniformly mixed phase of α-CsPbI 2 Br was shown to be highly susceptible towards a phase transformation into β-CsPbI 2 Br when halide interstitial or halide vacancy defects were introduced into the lattice. The rotation of PbI 4 Br 2 octahedra in α-CsPbI2Br allows it either to transform into a highly unstable apical β-CsPbI 2 Br, which may phase-segregate and is susceptible to CFD, or to phase-transform into equatorial β-CsPbI 2 Br, which is resilient against the deleterious effects of hole oxidation (energies of oxidation >0 eV) and demixing (energy of mixing <0 eV). Thus, the selective preparation of equatorial β-CsPbI 2 Br offers an opportunity to obtain a mixed perovskite material with enhanced photostability and an intermediate bandgap between its constituent perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2026

U.S. Distribution Transformer Demand Phase III - Key Drivers and Managing Demand [Slides]

This presentation demonstrates a significant analysis, on forecasting the demand for distribution transformers. The analysis is conducted for the United States, estimating the initial in-service capacity of these assets, and forecasting demand for these assets through 2050 with several sensitivities conducted. It examines not only demand for these assets, but importantly, how utility planning practices can impact the demand for theses assets in time. Under load growth scenarios, whether utilities practice like-for-like replacement strategies as failures occur, or whether they practice proactive up-sizing, anticipating electric load growth, can have major impacts on future demand. It also examines several other growth factors, such as the increasing demand for step-up transformers, which share many of the same characteristics as distribution transformers, and the demand for specific transformers for large project growth from data centers.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2026

Oxide nucleation via threshold-driven volume instability in Ni oxidation

Oxide nucleation dictates the onset of metal oxidation, yet the atomistic pathways bridging initial oxygen adsorption to bulk phase transformation remain elusive. Here, we utilize in-situ atomic-resolution imaging to directly capture the nucleation of nickel oxide, revealing a threshold-driven, cooperative transformation of Ni into NiO. Our observations identify a distinct incubation period during which oxygen progressively accumulates in subsurface layers. Once a critical concentration and penetration depth are reached, a collective lattice reconfiguration is triggered, abruptly converting multiple Ni layers into NiO. Atomistic simulations corroborate this mechanism, identifying a cooperative lattice instability induced by subsurface oxygen saturation. These results establish subsurface oxygen incorporation as the missing mechanistic link between surface adsorption and three-dimensional oxide formation, providing an atomistic framework to understand and control reactive phase transformations in materials synthesis, catalysis, and degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

First-Principles and Thermodynamic Simulation of Elastiс Stress Effect on Energy of Hydrogen Dissolution in Alpha Iron

Mobile hydrogen, when dissolving in metals, redistributes due to the density gradients and elastic stresses, and enables destruction processes or phase transformations in local volumes of a solvent metal. It is rather important in solid state physics to investigate these interactions. The first-principle calculations performed in terms of the density functional theory, are used for thermodynamic simulation of the elastic stress effect on the energy of hydrogen dissolution in α-Fe crystal lattice. The paper presents investigations of the total energy of Fe–H system depending on the lattice parameter. As a result, the relation is obtained between the hydrogen dissolution energy and stress. A good agreement is shown between the existing data and simulation results. The extended equation is suggested for the chemical potential of hydrogen atom in iron within the local stress field. Two parameters affecting the hydrogen distribution are compared, namely local stress and phase transformations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

From classical thermodynamics to phase-field method

Phase-field method is a density-based computational method at the mesoscale for modeling and predicting the temporal microstructure and property evolution during materials processes. The focus of this article is on connecting the most common phase-field equations to the very basic first and second laws of classical thermodynamics through rudimentary irreversible thermodynamics. It briefly discusses the relations of the continuum phase-field equations to their counter parts at the microscopic and atomic levels. It attempts to clarify the contributions of long-range elastic, electrostatic, and magnetic interactions to domain structure evolution during structural, ferroelectric, and ferromagnetic phase transformations by separating order parameter changes due to the presence of quasi-static fields and those arising from phase transformations. A few examples are presented to demonstrate the possibility of employing the phase-field method to provide guidance to designing materials for optimum properties or discovering novel mesoscale phenomena or new materials functionalities. Here, the article ends with a brief perspective on a number of potential future directions on the development and applications of phase-field method beyond its traditional applications to structural alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fabrication and characterization of a novel β metastable Ti-Mo-Zr alloy with large ductility and improved yield strength

Highlights: • Ti-12Mo-5Zr alloy exhibits excellent combination of improved yielding strength (>650 MPa), high ductility (uniform elongation ≈30%) and work-hardening behaviour. • The superior performances arise from the synergic effects between phase transformation induced plasticity and twinning induced plasticity. • The ‘d-electron’ alloy design approach in Ti-12Mo-5Zr alloy, i.e. Zr substitution to Ti, validates the feasibility of yielding stress improvement of TWIP/TRIP titanium alloys. - Abstract: In this paper, a novel ternary β-metastable titanium alloy, Ti-12Mo-5Zr (wt%), was designed based on the “d-electron” alloy design theory. The Ti-12Mo-5Zr alloy displays excellent combination of improved yielding stress (>650 MPa), high ductility (uniform elongation ≈30%) and work-hardening behaviour. The detailed microstructural analysis indicates that the superior performances arise from the synergic effects between phase transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP). Conforming to the design strategy, the improvement of mechanical performance results from the addition of Zr alloying element in substituting Ti, attributing to solution hardening effect and the increasing of critical resolved shear stress (CRSS) of stress induced martensitic transformation (SIM α″).

36 MATERIALS SCIENCE↗
DOE OSTI2016

Texture development during rolling of α+β dual-phase ZrNb alloys - 2016-0070

The texture evolution during high-temperature rolling (800 deg. C) of two model zirconium-niobium alloys was studied using electron backscatter diffraction. The aim was to decouple the relative importance of deformation and phase transformation on the final texture in an effort to elucidate the origin of the strong α-transverse basal texture commonly found in the hot-rolled product. The analysis uses a reconstruction software based on the Burgers relation to reconstruct the high-temperature β orientations, with the indexed α as input. In the low niobium content alloy, the texture evolution of the {11 2-bar 0}<10 1-bar 0> component was consistent with deformation in both α and β phases, along with a variant selection mechanism that occurred during the β → α phase transformation. Variant selection was observed to depend on the orientation of the deformed prior β grains. In the high niobium content alloy, a lower α volume fraction during hot rolling gave rise to different β textures and promoted the formation of a Goss component. This contributed to the {11 2-bar 0} <10 1-bar 0> component upon cooling, with variant selection enhanced by anisotropic grain breakup. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Heat Input on Weld-Bead Geometry, Surface Chemical Composition, Corrosion Behavior and Thermal Properties of Fiber Laser-Welded Nitinol Shape Memory Alloy

Bead-on-plate laser welding was carried out on 1-mm-thick Nitinol sheets at different heat input values. The variations in weld-bead geometry and variations in microstructures across the bead were studied. The effects of heat input on surface layer composition of the welded samples, corrosion properties and phase transformation temperature were examined. From x-ray photoelectron spectroscopy (XPS), it was clear that relative intensity of elemental Ni peak was higher in parent material and the oxidation state of Ti was Ti{sup 4+}. It was further observed from Auger electron spectroscopy (AES) that the Ti to Ni ratio on the top surface of the welded samples was more than 1, and as a result of this the stability of TiO{sub 2} layer was enhanced, which eventually helped to improve the corrosion property of the welded samples. The polarization resistance of the welded samples was increased by more than ten times compared to that of the un-welded samples. From differential scanning calorimetry (DSC), it became evident that phase transformation temperatures got changed due to welding.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A novel reduction synthesis of the graphene/Mn{sub 3}O{sub 4} nanocomposite for supercapacitors

Graphene/Mn{sub 3}O{sub 4} nanocomposite is successfully synthesized from graphene oxide (GO)/MnO{sub 2} precursor using dilute hydrazine hydrate assisted hydrothermal reaction (DAH method). X-ray photoelectron spectroscopy (XPS) and Raman characterizations confirm the decrease of oxygen-containing functional groups of GO. The results indicate that GO have been reduced to graphene to a large degree to increase the electronic conductive channels. The morphology and the phase transformation of MnO{sub 2} can be ascribed to the “dissolution-recrystallization” mechanism. Such nanocomposite, as electrode material for supercapacitor, exhibits a high specific capacitance of 326.9 F g{sup −1}, almost 4 times that of GO/MnO{sub 2} precursor (81.3 F g{sup −1}). The good cycle stability of 94.6% capacitance retention after 1000 cycles, can be explained by the firm interfacial cohesion between graphene and Mn{sub 3}O{sub 4} nanoparticle. This soft chemical DAH process could be readily extended to the preparation of other classes of hybrids. - Graphical abstract: The phase transition can be explained by the “dissolution-recrystallization” model. The GO/MnO{sub 2} precursor is reduced into graphene/Mn{sub 3}O{sub 4} by the DAH process, and the electrochemical property is dramatically enhanced. - Highlights: • Graphene/Mn{sub 3}O{sub 4} nanocomposite is firstly synthesized successfully from GO/MnO{sub 2} precursor. • The phase transformation from MnO{sub 2} to Mn{sub 3}O{sub 4} has occurred. • The specific capacitance of the graphene/Mn{sub 3}O{sub 4} (326.9 F/g) is 4 times that of GO/MnO{sub 2} precursor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Eliminating Voltage Decay of Lithium-Rich Li 1.14 Mn 0.54 Ni 0.14 Co 0.14 O 2 Cathodes by Controlling the Electrochemical Process

Lithium-rich material owns a particularly high capacity owing to the activation of electrochemical inactive Li 2 MnO 3 phase. But at the same time, MnO 2 phase formed after Li 2 MnO 3 activation confronts a severe problem of converting to spinel phase, and resulting in voltage decay. To our knowledge, this phenomenon is inherent property of layered manganese oxide materials and can hardly be overcome. Based on this, unlike previous reports, herein we design a method for the first time to accelerate the phase transformation by tuning the charge upper-limit voltage at a high value, so the phase transformation process can be finished in a few cycles. Then material structure remains stable while cycling at a low upper-limit voltage. By this novel method voltage decay is eliminated significantly.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗