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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Friction extrusion of ODS copper rod made from powder

Meters-long oxide dispersion strengthened copper rods were manufactured directly from powder by a single-step process, called friction extrusion. The average grain size was 880 nm, which was refined 40 times from powder precursor due to extensive shear deformation. Meanwhile, the average size of alumina particles was 60 nm which retains a decent oxide dispersion strengthening. Here, mechanical properties, including hardness, tensile strength, and ductility, were tested and found to have better or similar values than conventional sintered-then-extruded oxide dispersion strengthened copper materials. The presented technique promises a convenient avenue for the fabrication of oxide dispersion strengthened copper from powder.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Gas permeation properties of amorphous zeolitic imidazolate framework membranes made by atomic/molecular layer deposition

Amorphous metal-organic framework (MOF) membranes are desirable because they may retain some of the molecular sieving properties of their crystalline counterparts while being free of grain boundary defects, which often hinder the consistent achievement of high membrane performance. However, current methods, like melting and compression, for fabricating amorphous MOF membranes involve multi-step processes that require the formation of a crystalline membrane first, that is then amorphized, and therefore, could be challenging to scale. Here, we utilize atomic/molecular layer deposition (ALD/MLD) of diethylzinc (DEZ) and 2-methylimidazole (2mIm) to directly synthesize ultrathin amorphous zeolitic imidazolate framework (aZIF) deposits on γ-alumina-coated α-alumina supports. As the number of ALD/MLD cycles increased from 10 to 300, gas permeances decreased while ideal selectivities increased. Mixture separation factors for C3H6/C3H8, CO2/N2, and H2/C3H8 as high as 4, 37, and 194, respectively, were obtained. At 200 °C and 2.5 bar equimolar feed of H2 and C3H8, a H2/C3H8 mixture separation factor of 185 is obtained with an H2 permeance of ca. 4.15x10-8 mol/m2-s-Pa (124 GPU). Additionally, the membrane achieves a CO2/N2 mixture separation factor of 37 at 25 °C and 1 bar with a CO2 permeance of ca. 3.96x10-8 mol/m2-s-Pa (118 GPU). Considering the vast array of compositionally distinct aZIFs that can be potentially deposited by this approach, an enormously large parameter space for membrane design is emerging to be explored.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of processing parameters and build orientation on microstructure and performance of AISI stainless steel 304L made with selective laser melting under different strain rates

Selective laser melting (SLM) process brings diverse potentials on geometry flexibility; therefore, it is more and more widespread to be employed in fabrication metal alloys served for industries. Nonetheless, a material characterization study is desired to carry on for better understanding the correlation among process, structure, microstructure, and performance. In the current study, the SLM fabricated AISI stainless steel 304L was fabricated with different process parameters and built orientations (horizontal, inclined, and vertical. The tensile behavior was evaluated under different strain rates (0.0001 /s, 0.001 /s, 0.01 /s, and 0.1 /s) and compared to the commercial cold-rolled and annealed counterpart. Grain structures, tensile strength, elongation-to-failure, strain rate sensitivity, work hardening, and fractographic analysis were evaluated in terms of the effect of energy density, build orientation, and strain rate. The output indicates the tensile strength increases with increasing strain rates. On the contrary, the elongation-to-failure shows a decreasing trend with strain rates. Tensile properties of specimens built in the horizontal and inclined orientations are more sensitive to strain rates due to the smaller dimension of grain structures. Tensile anisotropy depends on the energy input, where a high energy density could yield a strong build orientation-dependent anisotropy. Hall-Petch relationship is validated to explain the mechanical anisotropy in different built orientations for SLM alloys. The strain hardening exponent and work hardening rate are demonstrated to be positively correlated, and they increase with smaller grain sizes. The fine dimple features indicate the ductile fracture mode regardless of strain rates. The size of the ductile dimples seems to depend on the strain rates and build orientations.

36 MATERIALS SCIENCE↗
DOE OSTI2023

SA508 low alloy steel to 316L stainless steel dissimilar metal joint made by powder metallurgy hot isostatic pressing

Joining ferritic SA508 low alloy steel (LAS) and austenitic 316 L stainless steel (SS) via powder metallurgy hot isostatic pressing (PM-HIP) was evaluated as an alternative method to welding. This study investigated the mechanical and microstructural evolutions of the bimetallic interface under different joint designs and heat treatments. Here, the direct joining of dissimilar metal alloys by PM-HIP method resulted in two designs: 1) powder SA508 to solid bar 316 L (P508–B316L) and 2) powder 316 L solid bar SA508 (P316L-B508). In both cases, P508–B316L and P316L-demonstrated satisfactory tensile strength, however, high hardness and severe depreciation in toughness were located on the bimetallic interface. The mechanisms responsible for the detrimental mechanical properties were verified. Large oxides were observed in P508–B316L due to the prior powder boundary (PPB) oxides present in SA508 powder. The intense sensitization occurred from the formation of M 23 C 6 carbides, consequently from the slow cooling after PM-HIP in P316L-B508. Post-HIP heat treatments were explored to reduce the distance of carbide formation; however, the heat treatment could not eliminate the carbides. The experimental results were compared to the diffusion couple simulation as a function of carbide formation with distance. The analysis also showed the high hardness at the bimetallic interface was primarily contributed by solid solution strengthening. In conclusion, the direct joining of P316L-B508 and P508–B316L via PM-HIP was deemed to be unfeasible, and a transitional material is necessary to impede the diffusion of carbon.

316L stainless Steel↗
DOE OSTI2022

Porosity evolution during heating of copper made from powder by friction extrusion

Here, friction extrusion was used to compact and extrude solid copper rod from feedstock powders. Following extrusion, considerable porosity was observed throughout the extrudate cross section due to the entrained porosity in the feedstock material and the extrusion process. The thermal stability of the extrudate was investigated via a series of heat treatments. Porosity evolution exhibited three distinct stages—an unchanged plateau (0°C–300°C) followed by an abrupt increase (400°C–500°C) and ultimately a reduction, as the temperature increases (>500°C). The peak porosity measured was ~25%. The underlying driving force for pore evolution is described as the competition between the internal pore pressure, material strength, and sintering kinetics, as a function of temperature. The observed porosity evolution and driving force are not expected to be limited to copper. Thus, this manuscript reveals an important consideration regarding elevated-temperature thermal stability as advanced manufacturing methods involving direct powder extrusion are explored.

36 MATERIALS SCIENCE↗
DOE OSTI2022

One hundred years into the study of ecotypes, new advances are being made through large-scale field experiments in perennial plant systems

A hundred years after Turesson first clearly described how locally adaptive variation is distributed within species, plant biologists are making major breakthroughs in our understanding of mechanisms underlying adaptation from local populations to the scale of continents. Although the genetics of local adaptation has typically been studied in smaller reciprocal transplant experiments, here it is being evaluated with whole genomes in large-scale networks of common garden experiments with perennial switchgrass and poplar trees. These studies support the hypothesis that a complex combination of loci, both with and without adaptive trade-offs, underlies local adaptation and that hybridization and adaptive introgression play a key role in the evolution of these species. Future studies incorporating high-throughput phenotyping, gene expression, and modeling will be used to predict responses of these species to climate change.

Trade-off↗
DOE OSTI2022

Carbon nanotube (CNT) reinforced 316L stainless steel composites made by laser powder bed fusion: Microstructure and wear response

Carbon nanotube (CNT) reinforced 316L stainless steel (SS) composites were fabricated by laser powder bed fusion (LPBF) additive manufacturing (AM). This study focuses on microstructure evolution, hardness, and wear behavior. The wear behavior for AM 316L SS and 1 wt% CNT/316L SS was studied by a dry sliding test under normal loads of 10, 15, and 25 N. The addition of CNT to 316L SS led to the change of solidification mode from cellular/columnar to dendritic growth, producing grain refinement. Nanoscale dendrites were observed. Although TEM characterization confirmed the existence of CNT in cell interior, most CNT were damaged, resulting in carbon material segregation along cellular/dendritic boundaries. The wear rate was found dramatically decreased due to the improved hardness. Compared to the adhesive and abrasive wear in AM 316L SS, the wear mechanism of CNT/316L composite was adhesion and oxidative wear. Furthermore, enhanced cellular/dendritic boundary strengthening by carbon segregation was the main strengthening mechanism of CNT/316L composite.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Family of Robust and Strongly Luminescent CuI-Based Hybrid Networks Made of Ionic and Dative Bonds

The CuI-derived inorganic–organic hybrid compounds are considered as promising phosphors for the lighting industry. Herein, exploiting N-monoalkylated hexaminium salts, [R-HMTA]X (R = Me, Et, Pr, and propargyl; X = Cl and I), as multibridging ligands, we have designed and synthesized a unique class of one-dimensional and two-dimensional hybrid CuI-materials. The reactions of these salts with CuI give rise to All-in-One (AIO) type compounds combining ionic and dative bonds between inorganic and organic components. The latter is formed by structurally unique inorganic [Cu x I y ] (y–x)– clusters, chains, or sheets interconnected through [R-HMTA] + cations via multiple Cu–N bonds. The so-designed compounds at ambient temperature exhibit tunable luminescence spanning from deep blue to red color (λ em = 430–625 nm) with microsecond lifetimes and the quantum efficiency of up to 78%. Remarkably, the AIO materials feature nontrivial excitation- (ED) and temperature-dependent (TD) luminescence, allowing their emission color to be finely adjusted from deep blue to red through changing the excitation wavelength and/or temperature. Based on the TD emission spectroscopy and theoretical calculations, a possible mechanism of the luminescence has been proposed. In conclusion, the very interesting luminescence characteristics coupled with good thermal and photostability render these AIO hybrid materials possible candidates for applications in energy-efficient lighting devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Pyrrophens: Pyrrole-Based Hexadentate Ligands Tailor-Made for Uranyl (UO 2 2+ ) Coordination and Molecular Recognition

Derivatives of a novel pyrrole-containing Schiff base ligand system (called “pyrrophen”) are presented which feature substituted phenylene linkers (R 1 = R 2 = H (H 2 L 1 ); R 1 = R 2 = CH 3 (H 2 L 2 )) and a binding pocket modeled after macrocyclic species. These ligands bind neutral CH 3 OH in the solid state through pyrrolic hydrogen-bonding. Here, the interaction of the uranyl cation (UO 2 2+ ) and H 2 L 1–2 yields planar hexagonal bipyramdial uranyl complexes, while the Cu 2+ and Zn 2+ complexes were found to self-assemble as dinuclear helicate complexes (M 2 L 2 ) with H 2 L 1 under identical conditions. The favorable binding of UO 2 2+ over Zn 2+ provides insight into the molecular recognition of uranyl over other metal species. Structural features of these complexes are examined with special attention to features of the UO 2 2+ coordination environment which distinguish them from other related salophen and porphyrinoid complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Ice Phase Classification Made Easy with Score-Based Denoising

Accurate identification of ice phases is essential for understanding various physicochemical phenomena. However, such classification for structures simulated with molecular dynamics is complicated by the complex symmetries of ice polymorphs and thermal fluctuations. For this purpose, both traditional order parameters and data-driven machine learning approaches have been employed, but they often rely on expert intuition, specific geometric information, or large training data sets. In this work, we present an unsupervised phase classification framework that combines a score-based denoiser model with a subsequent model-free classification method to accurately identify ice phases. Further, the denoiser model is trained on perturbed synthetic data of ideal reference structures, eliminating the need for large data sets and labeling efforts. The classification step utilizes the smooth overlap of atomic position (SOAP) descriptors as the atomic fingerprint, ensuring Euclidean symmetries and transferability to various structural systems. Our approach achieves a remarkable 100% accuracy in distinguishing ice phases of test trajectories using only seven ideal reference structures of ice phases as model inputs. This demonstrates the generalizability of the score-based denoiser model in facilitating phase identification for complex molecular systems. The proposed classification strategy can be broadly applied to investigate structural evolution and phase identification for a wide range of materials, offering new insights into the fundamental understanding of water and other complex systems.

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

Third-Order Møller–Plesset Theory Made More Useful? The Role of Density Functional Theory Orbitals

The practical utility of Møller–Plesset (MP) perturbation theory is severely constrained by the use of Hartree–Fock (HF) orbitals. It has recently been shown that the use of regularized orbital-optimized MP2 orbitals and scaling of MP3 energy could lead to a significant reduction in MP3 error. In this work, we examine whether density functional theory (DFT)-optimized orbitals can be similarly employed to improve the performance of MP theory at both the MP2 and MP3 levels. We find that the use of DFT orbitals leads to significantly improved performance for prediction of thermochemistry, barrier heights, noncovalent interactions, and dipole moments relative to the standard HF-based MP theory. Indeed, MP3 (with or without scaling) with DFT orbitals is found to surpass the accuracy of coupled-cluster singles and doubles (CCSD) for several data sets. We also found that the results are not particularly functional sensitive in most cases (although range-separated hybrid functionals with low delocalization error perform the best). As such, MP3 based on DFT orbitals thus appears to be an efficient, noniterative O(N 6 ) scaling wave-function approach for single-reference electronic structure computations. Scaled MP2 with DFT orbitals is also found to be quite accurate in many cases, although modern double hybrid functionals are likely to be considerably more accurate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗