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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Solvent-Free Coating of Organic Semiconductor Membranes with Centimetric Crystalline Domains

Organic semiconductors (OSCs) have shown great promise in a variety of applications. Although solution processing of OSCs has resulted in high-quality films, exquisite control of structural development to minimize defect formation during large-scale fabrication remains formidable. Compounding this challenge is the use of halogenated organic solvents, which poses significant health and environmental hazards. However, the solvent-free techniques introduced thus far impose additional limitations on solidification kinetics; the resulting OSC thin films are often more defective than those processed from solution. Here, a solvent-free technique is reported to prepare OSC membranes with centimetric crystalline domains. Leveraging the tendency for liquid crystalline materials to preferentially orient, OSCs are “prealigned” by depositing them from the melt over a metal frame to form a freely suspended membrane. Additionally, crystallization from this prealigned phase affords membranes with unprecedented structural order across macroscopic distances. Field-effect transistors comprising membranes of dioctyl[1]-benzothieno[3,2-b][1]benzothiophene (C8BTBT) and didodecyl[1]-benzothieno[3,2-b][1]benzothiophene (C12BTBT) having centimeter-sized domains as active layers exhibit a hole mobility of ≈8.6 cm2 V -1 s -1 , superseding the mobility of any transistors whose active layers are deposited from melt. This technique is scalable to yield membranes with large crystalline domains over wafer dimensions, making it amenable for broad applications in large-area organic electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Microstructural Engineering of Cu-Rich Nanoprecipitate formation in NiCoFeCrCu0.12 High-Entropy Alloy via Severe Plastic Deformation for Enhanced Irradiation Tolerance

This study demonstrates a defect-engineering approach for controlling Cu-rich precipitates in FeNiCrCoCu0.2 high-entropy alloys (Cu-HEAs), delivering a novel pathway for next-generation nuclear reactor materials with superior irradiation resistance. This work establishes that severe plastic deformation (SPD) processing via Shear Assisted Processing and Extrusion (ShAPE) and Friction Stir Layer Deposition (FSLD) creates dense dislocation networks and subgrain boundaries that fundamentally alter precipitation behavior under identical thermal treatments. Atom probe tomography (APT) indicates that SPD produces a metastable, atomically homogeneous solid solution that, upon moderate heat treatment (500°C/10 hour), develops remarkedly stronger Cu clustering than the as-cast counterpart. High-temperature exposure (800°C/100 h) produces near-pure Cu precipitates (~90 at% Cu) with significantly enhanced defect-sink efficacy in SPD-processed alloys: precipitate sizes of 50-60 nm and number densities of 2.7-3.8 × 10¹7 m?³, compared to 89 nm and 0.44 × 10¹7 m?³ in as-cast materials. Collectively, the findings establish defect-mediated precipitation control as a scalable, high-impact route to tailor sink density and distribution in HEAs, enabling microstructures optimized for irradiation tolerance and mechanical robustness in nuclear reactor environments.

Meher, Subhashish↗
DOE OSTI2026

Electro-chemo-mechanically Driven Ni Exsolution from (Pr,Ce,Ni)O 2−δ : Controlled Nucleation Density and Enhanced Electrode Kinetics

In situ exsolution of metal nanoparticles is a promising strategy to prepare electrocatalysts with enhanced activity and resistance to agglomeration for efficient chemical transformations and energy conversion. Achieving a high nucleation density of nanoparticles under mild conditions and understanding how to tailor the process is important for performance of these electrodes in electrochemical cells. In this work, we demonstrate facile exsolution of Ni nanoparticles using fluorite-structured (Pr,Ce)O 2−δ as the support oxide, driven by electrochemical potential and aided by the metastability of Ni in the solid solution (elastic driving force). We prepare single-phase oriented thin films of (Pr,Ce,Ni)O 2−δ (NPCO) on (Zr,Y)O 2−δ (YSZ) substrates by pulsed laser deposition. With the aid of a high-throughput electrochemical cell that provides a lateral gradient in Nernst voltage, we apply in situ near-ambient pressure synchrotron X-ray photoelectron spectroscopy and ex situ atomic force microscopy to investigate the impact of electrochemical potential on Ni nucleation density. We find that metallic Ni can be successfully exsolved at 550 °C upon cathodic biasing in 20 mTorr O 2 , and its nucleation density increases with increasing electrochemical driving force/decreasing oxygen chemical potential. We further evaluate the electrochemical performance under highly reducing (fuel electrode) conditions by electrochemical impedance spectroscopy. With the exsolved Ni nanoparticles, the surface exchange coefficient of the NPCO is found to be ∼4× higher than for PCO without exsolution. This work confirms mixed conducting fluorites as beneficial host lattices for facile transition-metal exsolution and suggests the possibility for constructing an all ceria-based electrochemical cell with PCO serving as both the cathode and the anode.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Direct ink writing techniques for in situ gelation and solidification

Direct ink writing (DIW) is an extrusion-based 3D printing method which prints near ambient temperatures and has one of the broadest printable material selections among additive manufacturing techniques. However, DIW uses viscoelastic materials susceptible to collapse during printing. Overall, one promising route to improve the structural integrity of viscoelastic inks is using in situ curing methods to increase the yield strength of the printed structures after deposition. This review summarizes progress in three representative methods of in situ curing for DIW, including ultra-violet-induced crosslinking, rapid cure of reactive ingredients, and flash vaporization of a solution’s solvent to coagulate dissolved polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Perovskite on Silicon Tandem Solar Cells

Since installing solar panels costs more than the panels themselves, it is critically important to improve the efficiency of the panels so that fewer panels need to be installed. More than 90% of all panels being manufactured are made with silicon solar cells. The most promising approach to reach 27% is to upgrade the panels by adding a second set of cells with a larger band gap that can harvest the higher energy photons in the visible spectrum and generate a higher voltage than silicon is capable of generating. Perovskite semiconductors are very promising for low-cost tandems because they have high band gaps, can be rapidly printed from solutions and have been used to make 25% efficient cells by themselves. If we show that it is possible to make stable tandems with 30% efficiency using materials that could be deposited at low cost and that the energy yield will not be compromised, then private companies would be able to raise the capital needed to manufacture this technology. The main metrics for this project are the power conversion efficiency of a lab-scale perovskite/silicon tandem and the ability to maintain a high power conversion efficiency in perovskite solar cells after accelerated operational stability testing under maximum power point at elevated temperature and 1 sun illumination. In short, this project demonstrates improvements to the perovskite absorber layer, contacts for the perovskite solar cell, and transparent oxide layers for window electrodes to achieve tandem efficiencies of 25% after one year and 27% after two years. By the end of the project, we identify strategies to further improve light management in the tandem devices and outline a pathway to reach 30%.In parallel, stability testing is conducted to evaluate said absorber and contact layers in the perovskite top cell, demonstrating 1000 hours of operation with less than 10% degradation at 1 sun. Our work on this project has made a leading impact on the development of perovskite/silicon tandems. The triple halide perovskite that we developed using iodide, bromide, and chloride and published in Science in March 2020 has received significant interest from other experts in the field at conferences. We took a silicon bottom cell with 21% efficiency, a technology that is responsible for a $30 billion market, and improved it by 30% relative. In addition, we have demonstrated impressive stability of our perovskite semitransparent top cells used in the tandems, showing for the first time packaged devices that pass a variety of IEC stability tests including damp heat, temperature cycling, and UV exposure tests.

14 SOLAR ENERGY↗
DOE OSTI2021

Perspectives of Open-Air Processing to Enable Perovskite Solar Cell Manufacturing

We report high throughput open-air processing techniques for the scalable production of all device and barrier layers for perovskite photovoltaics (PV). This work discusses and resolves some of the most formidable barriers to module-level scaling that the perovskite community has been facing. Our advanced technoeconomic manufacturing analysis indicates that vacuum-based processes with high capital expenditures (CapEx) and low throughputs dominate the cost of production. Open-air fabrication methods offer low CapEx routes to manufacturing, but achieving reproducibility in ambient conditions with varying relative humidity has been a persistent challenge. The use of rapid processing methods with plasma curing to convert films from the solution-state enables reproducibility, moisture immunity, and the highest perovskite PV efficiency produced in open-air. These methods are readily translatable to in-line processing where layers are sequentially deposited without the need for lengthy post-annealing steps that reduce throughput and involve additional equipment. Significant progress is demonstrated in reduced manufacturing costs as perovskites contend as a commercially viable next-generation thin film PV technology.

14 SOLAR ENERGY↗
DOE OSTI2022

High Volume Production of Nanoscale Elements

The utility of nanoscale elements spans numerous potential markets including healthcare, communications, energy, optics, and structures. The energy market in particular will require large volumes and is price sensitive. In this talk we will discuss strategies to scale nanoscale elements, including nanoparticle inks and nanoscale thin films, for the large area deposition (hundreds of square meters) using high through put processes. Historically, roll-to-roll production of thin films has been carried out at very high speeds over large areas using solution phase inks. Nanoparticles are produced in a bottom-up approach in solution phase that simplifies the processing and is amenable to ink formulations. Sintering and annealing of the thin films can be increased by using radiation thermal processing that integrates easily into roll-to-roll manufacturing. Results of printed films on the order of tens of nanometers to hundreds of nanometers are presented including studies of morphologies and uniformity over large areas. Solar cells devices using the roll-to-roll setup are demonstrated and a techno-economic analysis of the manufacturing is proposed. These results are presented with a comparison to the current photovoltaic technologies in production.

Druffel, Thad↗
DOE OSTI2024

Sequential formulation of all‐way coupled finite strain thermoporomechanics for largely deformable gas hydrate deposits

We develop a numerically stable sequential formulation of thermoporomechanics for largely deformable gas hydrate deposits, extended from the fixed stress split of infinitesimal transformation. Constitutive equations are based on the total Lagrangian approach for both flow and geomechanics, including dynamic full tensor permeability and thermal conductivity updated from the deformation gradient. For space discretization, we take the cell-centered finite volume and node-based finite element method for flow and geomechanics, respectively. Then, we propose a sequential implicit method for all-way coupled thermoporomechanics, where the nonisothermal multiphase flow problem of gas hydrates is solved implicitly first and then the geomechanics problem is solved implicitly at the next step. During solution of the flow problem, we fix the rate of first Pioal total stress for numerical stability as well as apply porosity correction and entropy correction to account for geomechanical effects. We test numerical examples where flow and geomechanics parameters are based on deep oceanic gas hydrate deposits. When applying depressurization, even though the results between the infinitesimal transformation and finite strain geomechanics are similar in the early stages due to small deformation, we find differences between them in the late times as deformation becomes large. Accordingly, permeability and thermal conductivity tensors become nonisotropic full tensors although they are initially isotropic. Furthermore, we identify numerical stability of the developed sequential method from the test cases that exhibit the highly complex coupled gas hydrate systems with large deformation. Thus, the proposed sequential formulation can be applied in largely deformable gas hydrate systems.

42 ENGINEERING↗
DOE OSTI2023

A phased workflow to define permit‐ready locations for large volume CO 2 injection and storage

Abstract To‐date, only two UIC Class VI permits have been issued by the US Environmental Protection Agency. We illustrate a four‐phase workflow to first identify regional storage resources and then down‐select sites to yield permit‐ready locations that can accept and store large volumes of CO 2 . Specific permit requirements should guide objectives and define deliverables of respective workflow phases. In the first phase we used available regional data and screened structure and injection zones to locate resources that match CO 2 volumes planned to be captured. Available data were also used to assess presence and depth of usable groundwater, the key resource being protected via permitting. We then used advanced, closed‐form, analytical solutions (EASiTool) to estimate CO 2 injectivity into each hydrologically connected injection compartment. In the second phase we acquired and conditioned additional wireline logs and leased available seismic datasets. We interpreted the depositional systems from wireline well‐log character and mapped sandbody geometry to interpolate injection and confining‐zone distribution. Using available data, we mapped faults and locations of freshwater and overpressure (or other capacity‐limiting geologic parameters) in more detail. In the third phase, we used the augmented geologic data to develop a static model for the selected area, extracted the areas of highest interest, and generated and ran dynamic (flow) models. In a fourth phase, we reduced major uncertainties identified in earlier phases. Our case study indicates that to complete preparation of a permit application requires (1) improved lithologic characterization information (thicknesses and horizontal and vertical connectivity) and (2) better definition of poorly defined local faults. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

58 GEOSCIENCES↗
DOE OSTI2023

Antireflective Multi‐Dielectric Metasurfaces Operating in the Visible

Abstract As increasingly more demanding photonics applications are brought on‐chip, more complex design solutions are employed to deliver enhanced performance: e.g., meta‐molecules, inverse‐designed freeform structures, and multilayer metasurfaces. Instead, this study introduces anti‐reflective metasurfaces fabricated in a single nanolithography step that follows deposition of multiple dielectrics onto a substrate. Anti‐reflective metasurfaces offer fundamentally better transmission efficiencies compared to conventional equivalents. Conventional and anti‐reflective metalenses, both fabricated in the Ta 2 O 5 /SiO 2 material platform for 461 nm operation, show an improvement in focusing efficiencies from ≈ 55% to ≈ 90% at low numerical apertures and from ≈ 35% to ≈ 65% at high numerical apertures. Simulations of ideal and imperfect metalenses indicate that anti‐reflective metasurfaces not only improve transmission at the design library level, but also reduce spurious diffraction and protect against higher‐order scattering.

Optics↗
DOE OSTI2024

Electrodeposited Mo x S y O z /Ni Tribological Coatings

Deposition of molybdenum disulfide (MoS 2 ) coatings using physical vapor deposition (PVD) and mechanical burnishing has been widely assessed for solid lubricants in space applications but still suffers from line-of-sight constraints on complex geometries. Here, we highlight one of the first demonstrations of electrodeposited Mo x S y O z and Mo x S y O z /Ni thin-film coatings from aqueous solutions of ammonium tetrathiomolybdate for solid lubricant applications and their remarkable ability to provide low coefficients of friction and high wear resistance. Characterization of the coating morphology shows amorphous microstructures with a high oxygen content and cracking upon drying. Even so, electrodeposited Mo x S y O z can achieve low steady-state coefficients of friction (μ ∼ 0.05–0.06) and wear rates (2.6 × 10 –7 mm 3 /(N m)) approaching those of physical vapor deposited coatings (2.3 × 10 –7 mm 3 /(N m)). Additionally, we show that adding dopants such as nickel increased the wear rate (7.5 × 10 –7 mm 3 /(N m)) and initial coefficient of friction (μ i = 0.23) due to compositional modifications such as dramatic sub-stoichiometry (S/Mo ∼ 1) and expression of a NiO x surface layer, although doping did reduce the degree of cracking upon drying.

Babuska, Tomas F.↗
DOE OSTI2026

Selective transport of light vs. heavy rare earth elements by sulfate/bisulfate complexes in hydrothermal fluids

Here, this study explores the transport of rare earth elements (REE) in acidic sulfate-bearing hydrothermal fluids and the implications for the fractionation of light/heavy REE in critical mineral deposits. The speciation of Nd (light REE) and Yb (heavy REE) sulfate complexes were determined via in situ Raman spectroscopy using fused SiO 2 capillary cells up to 300 ºC at saturated water vapor pressure and in a hydrothermal diamond anvil cell up to 500 ºC and 540 MPa. The REE monosulfate (REESO 4 + ) and REE disulfate (REE(SO 4 ) 2 - ) species are stable below 150 to 250 ºC but become less stable at higher temperatures, particularly the light REE, due to the decreased solubility of REE sulfate solids. At higher pressure, these REE sulfate complexes display an increased stability field up to 400 ℃. The REE bisulfate complex (REEHSO 4 2+ ) was identified with a wide stability field below 400 ºC for the HREE in acidic Yb 2 (SO 4 ) 3 -bearing solutions, whereas in Nd 2 (SO 4 ) 3 -bearing solutions, the LREE bisulfate complex is restricted to below 100 ℃. These results suggest that bisulfate is a previously unrecognized selective ligand for heavy REE transport at low temperature in acidic oxidized hydrothermal fluids. Such fluids are responsible for hydrothermal alteration in many REE deposits. Prediction of phase stabilities across pressure, temperature, and composition space (P-T- x ) is crucial for predicting the role of aqueous REE sulfate complexes in the mobilization of REE in crustal fluids.

58 GEOSCIENCES↗
DOE OSTI2021

In situ Al 2 O 3 incorporation enhances the efficiency of CuIn(S,Se) 2 solar cells prepared from molecular-ink solutions

Here, we report an efficiency enhancement of solution-processed CuIn(S,Se) 2 (CISSe) thin film solar cells via in situ incorporation of Al 2 O 3 . These films were produced using inks containing CuCl, InCl 3 , AlNO 3 (Al/Al + In: 0.1) and thiourea dissolved in methanol. After spin coating of these solutions in air, samples were subjected to a selenization process. Auger electron spectroscopy depth-profiling analysis showed that Al is evenly distributed throughout the bulk of the film. Transmission electron microscopy revealed that AlNO 3 precursor reacted with oxygen to form nanosized amorphous Al 2 O 3 grains located within the bulk and grain boundaries of CISSe, as well as at both the top and bottom interfaces. Power conversion efficiency (PCE) as high as 11.6% (JS C : 35.8 mA cm –2 , V OC : 518 mV, FF: 62.2%, no anti-reflection coating) was achieved with Al–CISSe solar cell devices integrated with CdS (chemical bath deposition, thickness: 80 nm) and ZnO/ITO bilayers (sputtered, thickness: 300 nm). The average PCE (10.1%, $\langle$J SC $\rangle$: 34.5 mA cm –2 , $\langle$V OC $\rangle$: 491 mV, $\langle$FF$\rangle$: 59.8%) was nearly 4% (absolute) higher than that measured on CISSe baseline cells fabricated from solutions without Al ($\langle$PCE$\rangle$ = 6.4%, $\langle$J SC $\rangle$: 32.8 mA cm –2 , $\langle$V OC $\rangle$: 410 mV, $\langle$FF$\rangle$: 47.3%). This in situ Al 2 O 3 incorporation is speculated to play a role in the enhancement of the VOC and FF of the devices through passivation of defects in CISSe reducing interface and bulk recombination, as evidenced by a reduced defect density and an increased activation energy of the dominant recombination mechanism from capacitance and temperature-dependent VOC measurements, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Moderate pH changes alter the fluxes, selectivities and limiting currents in ion transport through polyelectrolyte multilayers deposited on membranes

Layer-by-layer (LBL) polyelectrolyte coatings on membranes are attractive for their high selectivities between monovalent and divalent ions. However, deposition of poly(4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) films on ion-exchange membranes leads to low ion fluxes that restrict productivity or current efficiency. This study shows that increasing the solution pH from 6.5 to 8.3 enhances cation fluxes and limiting currents through (PAH/PSS) 5 PAH-coated cation-exchange membranes while still achieving order of magnitude selectivity increases compared to bare membranes. In Donnan dialysis through (PAH/PSS) 5 PAH-coated Nafion, at pH 8.3 the K + /Mg 2+ selectivity is 100, and the K + flux is 22 times that at pH 6.5. Moreover, at the higher pH the electrodialysis limiting current through these membranes increases ~5-fold. This enables electrodialysis separation of K + and Mg 2+ with a current efficiency around 0.75, a selectivity of 18, and 50% K + recovery from the source phase. Transmembrane potential measurements and increases in Cl - /SO 4 2- selectivities (from 9.5 at pH 6.5 to ~70 at pH 8.3) for porous alumina membranes coated with (PSS/PAH) 5 PSS films suggest that the coating becomes cation-permselective at higher pH. Increased cation transference numbers in polyelectrolyte coatings likely lead to the enhanced limiting currents for coated Nafion at higher pH. Lastly, (PAH/PSS) 5 PAH-coated Nafion shows a Li + /Mg 2+ Donnan dialysis selectivity >700 at neutral pH and a selectivity of 10 at pH 8.3. However, the Li + flux is 6 times greater at pH 8.3, which might make operation at the higher pH desirable.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Tuning Surface Stoichiometry of SOFC Electrodes at the Molecular and Nano-scale for Enhanced Performance and Durability

This project achieved the following objectives. Different cation segregation behaviors of different common SOFC cathodes, including La 0.6 Sr 0.4 Co0.2Fe 0.8 O 3-δ (LSCF), Sr 0.5 Sm 0.5 O 3-δ (SSC), and PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O5 +δ (PBSCF), were determined. We showed how oxygen partial pressure and gas impurities impact the stability of SOFC cathodes. We developed atomic layer deposition (ALD) coating techniques for electrodes and showed that by introducing different elements and different ALD oxidizers, electrode surface chemistry can be altered, resulting in enhanced oxygen reduction kinetics. In addition, we developed solution infiltration technique to enhance performance and durability of electrodes. Different infiltrates as well as different thermal treatment processes were screened to identify the optimal surface modification process that yields both low impedance and high durability. The modified cathode shows excellent stability and has a low area specific resistance (ASR) of only 0.2 Ωcm 2 at 600 °C after over 2000 hours of operation. Further, we developed ceramic anodes, SrFe(Co,Mo)O 3 (SFCM) and SrFe(Ni,Mo)O 3 (SFNM), and enhanced anode oxidation kinetics by solution infiltration or in situ catalyst exsolution from the ceramic anode surface. The modified anodes showed improved performance in full SOFCs, and the optimized anode modification shows high stability for over 400 hours at 550 °C. Moreover, the modified anode also demonstrates high durability in methane. This work provides fundamental understanding of electrode surface chemistry and demonstrates a simple, facile, cost-effective approach to enhance catalytic activity and durability of SOFC electrodes.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2022

Uniform lithiophilic layers in 3D current collectors enable ultrastable solid electrolyte interphase for high-performance lithium metal batteries

Uniform lithium plating/stripping during charging/discharging in 3D lithiophilic current collectors (3DLCC) is essential to suppress growth of lithium dendrites and to mitigate infinite volume variations of lithium metal for long-lived lithium metal batteries. Additionally, this study reveals the decisive role played by uniformity of the lithiophilic layer of the 3DLCC in achieving uniform lithium plating/stripping. Herein, a series of metal oxide-based 3DLCCs are successfully fabricated with a simple and an ultrafast solution combustion method, from which formation of a uniform and stable lithium dendrite-free solid electrolyte interphase via a uniform lithiophilic layer is demonstrated. Taking Co 3 O 4 as the lithiophilic material deposited on a nickel foam as the 3DLCC (Co@NF) for a proof of concept, the loading amount of Co 3 O 4 , closely correlated with the uniformity of the Co 3 O 4 layer, is modulated to optimize its lithium ion hosting performances. With a uniform Co 3 O 4 layer grown in the 3DLCC, an ultralow nucleation overpotential of 33.4 mV is achieved in half-cell tests at 1 mA cm -2 and 1 mAh cm -2 , and a high Coulombic efficiency of 97.1% is maintained after 210 cycles under a severe cycling condition of 2 mA cm -2 and 1 mAh cm -2 . A small polarization voltage of 13 mV together with an ultralong cycle life of 2400 h at 0.5 mA cm -2 and 1 mAh cm -2 in symmetric Li cells is achieved. Moreover, the composite Li anode delivers sensational rate capability and cyclability in full-cells. This work not only provides new and valuable insights into the interphasial chemistry of solid electrolyte interphase layers, but also sheds light on the development of ultrastable lithium metal batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Optical properties of Mo and amorphous MoOx, and application to antireflection coatings for metals

To form antireflection (AR) coatings to hide metal architecture in display technologies, we deposited thin films of metal Mo and oxide MoOx by sputtering targets of various compositions using pure Ar sputter gas. The optical constants [n,k] of these samples were measured by the direct numerical solution of reflectance and transmittance at each wavelength point measured. We find that 50 nm films are uniform in the growth direction, but for thicker 100 nm samples, evidence exists for nonuniform growth, where the top 20 nm appears to be metal rich. From these [n,k], negative Tauc bandgap energies show these oxides are semi-metals. We then identified the specific composition (x) that optimizes the AR response for a host of metals (Al, Cu, Ag, Au). Finally, two methods were used to understand why these MoOx materials function well as AR media, including (i) using phasor rays and (ii) developing a universal expression for the AR condition that applies to both dielectric and metal substrates. In (i), we find two characteristics for AR of metals: (a) its optical thickness should be roughly π3, not the π2 for dielectrics, since for MoOx, their [r^ij,t^ij] Fresnel phases differ from the usual [180°, 0°] of dielectrics; and (b) the medium incorporates a k-dominant strategy whose function is to absorb the energy that is reflected at the AR/metal interface. In (ii), the universal AR condition is found to be r^01+r^12z^=0. For dielectrics, this reduces to the well-known nAR=nairnsub condition. However, for metals, a concise analytic expression is lacking since this expression is highly nonlinear but is easily solved by numerical methods.

Tsu, David V. (ORCID:0000000295903418)↗
DOE OSTI2020

Laser metal deposition of refractory high-entropy alloys for high-throughput synthesis and structure-property characterization

Progress in materials development is often paced by the time required to produce and evaluate a large number of alloys with different chemical compositions. This applies especially to refractory high-entropy alloys (RHEAs), which are difficult to synthesize and process by conventional methods. To evaluate a possible way to accelerate the process, high-throughput laser metal deposition was used in this work to prepare a quinary RHEA, TiZrNbHfTa, as well as its quaternary and ternary subsystems by in-situ alloying of elemental powders. Compositionally graded variants of the quinary RHEA were also analyzed. Our results show that the influence of various parameters such as powder shape and purity, alloy composition, and especially the solidification range, on the processability, microstructure, porosity, and mechanical properties can be investigated rapidly. The strength of these alloys was mainly affected by the oxygen and nitrogen contents of the starting powders, while substitutional solid solution strengthening played a minor role.

additive manufacturing↗