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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Analysis of thermal history effects on mechanical anisotropy of 3D-printed polymer matrix composites via in situ X-ray tomography

The tensile behavior of an additively manufactured (AM) polymer matrix composite (PMC) is studied with in situ X-ray computed microtomography (CT) and digital volume correlation (DVC). In this experiment, the effects of recycled material content and print direction on the selective laser-sintered (SLS) material's mechanical response are explored. The PMC samples are printed in a tensile specimen geometry with gage lengths parallel to all three orthogonal, primary sintering directions. In situ tensile-CT experiments are conducted at Argonne National Laboratory's Advanced Photon Source 2-BM beamline. Analysis of the AM PMC's tensile response, failure, and strain evolution is analyzed both from a conventional standpoint, using the load-displacement data recorded by the loading fixture, and from a microstructural standpoint by applying DVC analysis to the reconstructed volumes. Significant variations on both strength and ductility are observed from both vantages with respect to print direction and the recycled material content in the printed parts. As a result, it is found that the addition of recycled source material with a thermal history reduces the tensile strength of the SLS composite for all directions, but the effect is drastic on the strength in the layering direction.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Lightweight TiC–(Fe–Al) ceramic–metal composites made in situ by pressureless melt infiltration

Lightweight ceramic–metal (cermet) composites combine stiffness and hardness with fracture toughness and ductility. TiC and Al are ideal pairs among lightweight cermet composites because of their relatively high strength-to-weight ratios, but these materials are difficult to process in solid state or with Al melt infiltration without making an aluminum carbide phase, which is detrimental to mechanical properties. Here, Fe is added to a TiC powder preform to reduce the activity of Al with TiC during Al melt infiltration and to aid in pressing TiC preforms, making a lightweight TiC–(Fe–Al) composite while avoiding other, unwanted phases. The composites are made by first pressing TiC powder mixed with Fe followed by Al melt infiltration; the result is a composite with high TiC content in a two-phase matrix, both of which are Fe–Al-based. The composite has low density, low porosity, high hardness, no detectable Al 4 C 3 phase with X-ray diffraction and retains shape well during infiltration.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermodynamics and kinetics of precipitation and austenite reversion during aging of Ti-free grade 300 maraging steel manufactured by laser powder bed fusion (LPBF)

Austenite reversion and intermetallic precipitation are two key phase transformations in maraging steels which determine the strength and ductility. Usually, an optimum aging temperature/time is determined using trial and error approach with inputs from thermodynamic databases and a-posteriori microscopy/hardness evaluations. In this study, a thermo-kinetic model is developed to predict the precipitation and austenite reversion kinetics during various post-fabrication heat treatments in a Ti-free variant of grade 300 maraging steel manufactured using laser powder bed fusion. The thermo-kinetic model was based on the principles of Scheil solidification and the classical nucleation theory. The predictions from the thermo-kinetic model were verified using suitable microscopy techniques, and the results from the thermo-kinetic model agree well with the experimental measurements. Overall, results highlight the fact that an Integrated Computational Materials Engineering approach can be used to predict the precipitation and austenite reversion kinetics, and be used as an input for an efficient design of heat treatments for achieving optimum mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructural refinement in ultrasonically modified A356 aluminum castings

Two A356 aluminum alloys (Al-Si-Mg), one with 0.09 wt.% Fe and one with 0.91 wt.% Fe, were cast in a graphite mold with the simultaneous application of local ultrasonic intensification to refine the as-cast microstructure. Ultrasonication during casting transformed the morphology of primary Al grains from dendritic (~140-290 microns in size) to globular (~33-36 microns in size). The alloy with high Fe exhibited globular grains at distances up to 45 mm away from the ultrasound probe, while the alloy with low Fe exhibited globular grains at distances only up to 6 mm away from the ultrasound probe. Near the location of the ultrasound probe (< 2 mm away), a second non-dendritic microstructural morphology was observed with fine aluminum grains (~9-25 microns in size). This unique fine-grained morphology has not been previously reported, contains a greater concentration of Si relative to the globular microstructure, and may be a large, fully eutectic region. Ultrasonication during casting also transformed the morphology of the ß-Al 5 FeSi phase particles (which are deleterious to the strength and ductility of the alloy) in the high Fe alloy from needle-like to rectangular, which could enable the greater use of secondary Al alloys. Thermodynamic simulations conducted to calculate the solidification paths of the two alloys studied predict that the ß-Al 5 FeSi phase begins to form earlier in the alloy with high Fe. Finally, data suggest that the ß-Al 5 FeSi phase (which is more abundant in alloys with high Fe content) may enhance ultrasonically-induced grain refinement.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Inhibition of Polyimide Photodegradation by Incorporation of Titanate Nanotubes into a Composite

The effect of UV light exposure on the properties of hexafluoroisopropylidene-diphthalic anhydride–oxydianiline (6FDA–ODA) polyimide (PI) and polyimide–titanate nanotube (TiNT/PI) composites has been studied using Raman spectroscopy, optical microscopy, nanoidentation and TEM. The degree of polymer photodegradation was estimated by measuring the change in affinity to a positively charged dye (methylene blue, MB). The mechanism of photoassisted transformations in polyimides usually involves scission of polymer chains accompanied by appearance of active radicals, which undergo further rapid transformations to more stable phenol, amine, and carboxylic functional groups. The accumulation of these groups can increase the degree of adsorption of charged dyes in the photodegraded polymer. It was found that neat PI showed a significantly increased capacity to adsorb MB after irradiation with UV, reaching a plateau after 1 h. In contrast, TiNT/PI composite demonstrated a much slower rise in concentration of adsorbed MB even after 4 h of UV exposure. Raman spectra indicated cleavage of C=O and C–F bonds in PI while only the C–F bond was damaged in TiNT/PI. Shorter cracks (≈ 40 µm long) appeared in TiNT/PI composites whereas macro cracks (> 100 µm) were visible in neat PI after 3 h of UV exposure. Brittleness was studied by comparing plasticity index which varied from 0 to 1 (0 corresponding to the most brittle material and 1 the most ductile one). Plasticity index reduced by 51% and 2% for PI and TiNT/PI, respectively after 3 h UV irradiation, indicating that TiNT can protect underlying PI from further damage. The hardness of neat PI decreased whereas, for TiNT/PI, it increased under UV, suggesting crosslinking of broken polymer chains with nanotubes. Graphical Abstract: Photodegradation of a titanate nanotubes/polyimide composite can lead to cross-linking of broken polymer chains by nanostructured material, resulting in increased hardness. .

36 MATERIALS SCIENCE↗
DOE OSTI2019

Modification of Poly(L-lactide) via a Pectinate Polymethylphenylsilane-co-poly(ε-caprolactone)

To solve the problem of the hard and brittle mechanical properties of poly(L-lactide) (PLLA), a novel pectinate polymethylphenylsilane-co-poly(ε-caprolactone) (PCL-PMPS-PCL) has been designed to modify PLLA via the hydrolysis polycondensnsation of methylphenyldimethoxysilane and ring-opening polymerization of ε-caprolactone. The triblock copolymer is characterized with {sup 1}HNMR and GPC. It is harmonized with PLLA in chloroform to make smooth blending film. Incorporation of PCL-PMPS-PCL lowers T{sub g} of PLLA, enhances the macromolecular mobility, and facilitates PLLA to form defective crystals. Compared to the brittle PLLA, the cross section of blends is rough and uneven. With the blending amount of PCL-PMPS-PCL going up, the tensile strength curve has a downward glacis, while the elongation at a break climbs upward, and reaches 25% at 10 wt%, exhibiting that the typical characteristics of ductile material. At the same time, the tensile strength for 10 wt% PCL-PMPS-PCL/PLLA reserve about 60 MPa, so PCL-PMPS-PCL can serve as a candidate of plasticizing PLLA.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermo-Mechanical Properties of Injection Molded Components Manufactured by Engineered Biodegradable Blends

Engineering of ductile, tough and thermal resistant PLA-based materials requires blending of PLA with other constituents by reactive twin-screw co-rotating extrusion to achieve compounds with adequate thermo-mechanical properties. Then, the compound of the polymeric blends must be melt processed to the final shape with an additional technology, namely the injection molding. The two-stage process the polymeric blends must undergo and the different rheological properties the blends must feature to be suitable to the different processing steps make extremely difficult to engineer the material. Extrusion compounding requires high viscous materials low melt flow index (MFI), while injection molding requires materials with low viscosity (high MFI). To overcome these shortcomings, this manuscript deals with the design of novel biodegradable PLA-based blends that rely on mixing PLA grades with different MFI (i.e. very low for extrusion and high for injection molding), each chosen to feature the rheological characteristics needed for each step of the two-stage transformation process. The ratio of the two PLA-grades inside the blends was the matter of the present investigation. The blends were subsequently tested for the manufacturing of single-use biodegradable and thermal resistant injection molded small cups, specifically designed for brewing of hot beverages. Lastly, the thermo-mechanical performance of the as-is and annealed cups were studied. Experimental evidences show blending of two-different grades of PLA is a promising route to formulate low impact polymeric materials suitable for demanding packaging solutions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Study of Electronic, Mechanical, Magnetic, and Optical Properties of Mg{sub 0.75}TM{sub 0.25}S/Se (TM = Fe, Co, Ni): A First Principle Approach

A systematic study of the magnetism, mechanical, and optical behaviors of Mg{sub 0.75}TM{sub 0.25}S/Se (TM = Fe, Co, Ni) ordered alloys was conducted using the full-potential linearized augmented plane wave plus local orbital method. The ferromagnetic (FM) and antiferromagnetic (AFM) ground state energy differences and enthalpy of formation scrutinized their dynamical stability in the FM state. The elastic parameters decided their mechanical stability, ductile behavior, and partial ionic and covalent characters. Moreover, the calculated band structures and density of states revealed the type and origin of magnetism in terms of exchange splitting energies and exchange constants. The Fe- and Ni-doped MgS/Se alloys exhibited half metallic ferromagnetic (HMF) characteristics, while the Co-doped MgS/Se alloy depicted ferromagnetic semiconducting characters. A reduction in the magnetic moments of the transition metals was observed compared with their free space value, which is due to strong p-d hybridization. Furthermore, the optical spectrum showed the maximum light absorbed in the visible and in the UV region of the electromagnetic spectrum, which makes them potential candidates for optoelectronic and spintronic device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic, Mechanical, and Electronic Properties of RhH{sub x} (x = 0, 0.25, 0.75, 1) from First-Principles Calculations

The magnetic, mechanical, and electronic properties of RhH{sub x} (x = 0, 0.25, 0.75, 1) have been investigated by first-principles calculations based on density functional theory. It is shown that RhH{sub x} (x = 0.25, 0.75, 1) in the cubic structure are magnetic except for Rh. The total magnetic moments of RhH{sub x} (x = 0.25, 0.75, 1) decrease with increasing content of H, which mainly results from the change of the Rh moments. The calculated elastic constants indicate that RhH{sub x} (x = 0, 0.25, 0.75, 1) in the cubic structure are mechanically stable. With increasing H content, the bulk modulus, shear modulus, and Young modulus gradually decrease except the bulk modulus of RhH. By means of the values of the B/G ratio, it is concluded that H doping improves the ductile properties of Rh. The strong hybridization between H-s and Rh-d is the origin of magnetism for RhH{sub x} (x = 0.25, 0.75, 1) and decreases with increasing H content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Electronic, Magnetic and Optical Investigations of Half-Heusler Compounds YZSb (Z = Cr, Mn): FP-LAPW Method

Half-Heusler compounds YZSb (Z = Cr, Mn) are theoretically explored in the framework of density functional theory (DFT). We have investigated a number of different properties with the help of the WIEN2k simulation package. Equilibrium lattice constants fall in the range 6.0–7.0 Å for both compounds. Elastic properties are also studied and it is found that the compound YCrSb is of brittle and YMnSb is of ductile nature as indicated by a number of parameters including Cauchy pressure, Pugh’s ratio and Poisson’s ratio. Electronically, these compounds are found to be half-metals as their spin-up states are semiconducting and hence 100% spin polarized at the Fermi level while spin-down states are conducting. The total magnetic moments are equal to 4μ{sub B} and 3.15μ{sub B} for YCrSb and YMnSb, respectively. The optical properties including dielectric function, reflectivity, refractive index, conductivity and absorption coefficients are calculated and discussed. Optical characteristics of the compounds hint that they are more active in the infrared region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Investigation on Electronic, Magnetic, Mechanical, and Thermodynamic Properties of AMO{sub 3} (A = Eu, M = Ga, In) Perovskites

The structural, electronic, magnetic, elastic, and thermodynamic properties of cubic AMO{sub 3} perovskites (A = Eu, M = Ga, In) have been successfully studied within density functional theory using full-potential linearized augmented plane wave (FP-LAPW). The structural study reveals that both the compounds are stable in ferromagnetic states. The GGA + U calculated spin-polarized electronic band and density of states present the half-metallic nature of both the compounds. The magnetic moments calculated with different approximations were found to be approximately 6 μ{sub B} for EuGaO{sub 3} and approximately 7 μ{sub B} for EuInO{sub 3}. From elastic calculation, the three independent elastic constants (C{sub 11}, C{sub 12}, C{sub 44}) have been acquired to yield the mechanical properties like Young modulus (Y ), shear modulus (G), Poisson ratio (ν), and anisotropic factor (A). The calculated values of B/G show that both the compounds are ductile in nature. The thermodynamic study was also accomplished by exploring the thermodynamic parameters like specific heat, heat capacity, thermal expansion, Grüneisen parameter, Debye temperature, etc. within the temperature range 0 to 900 K and pressure range 0 to 50 GPa.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A Density Functional Theory Investigations of Half-Heusler Compounds RhVZ (Z = P, As, Sb)

We have studied the half-Heusler compounds RhVZ (Z = P, As, Sb) using Density Functional Theory (DFT). The method of the Full Potential Linearly Augmented Plane Wave (FP-LAPW) is employed in the Wien2k package for calculation of structural, elastic, mechanical, electronic, magnetic, and optical properties. Lattice constants are found in the range 5.67 − 5.80 Å. Analysis of elastic properties shows that two of the compounds namely RhVP and RhVAs are ductile while RhVSb is brittle in nature. All three compounds are half-metals as revealed from the band structures and Density of States (DoS) calculations. In all of them, spin-down channels have the small band gaps, while spin-up channels are conducting. These compounds follow the Slater-Pauling 18 (M{sub Tot} = Z{sub Tot} − 18) electron rule with the total magnetic moments in the range 1 − 2 μ{sub B}. Optical properties like dielectric function, refractive index, reflectivity, conductivity, and absorption coefficient are calculated and discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Theoretical Investigations of Properties of New Half-Heusler Compounds NiFeZ (Z = Si, Ge)

The half-Heusler alloys NiFeZ (Z = Si, Ge) are investigated theoretically in the general framework of Density Functional Theory (DFT). We have calculated structural, mechanical, elastic, electronic, magnetic, and optical properties using WIEN2k simulation package. To incorporate the electronic exchange-correlation energy we have used the GGA+U approximation. Both the compounds are found structurally stable, however, elastic properties show that NiFeSi is ductile while NiFeGe is brittle. Electronically, the compounds are found to be half-metals with small band gaps in the spin-down channels whereas spin-up channels are conducting. The total magnetic moments for both the compounds are ≈ 2μ{sub B}. Optical properties including dielectric function, refractive index, extinction coefficient, reflectivity, conductivity, and absorption coefficient are also calculated and analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Theoretical Study of Structural, Magnetic, Elastic, Phonon, and Thermodynamic Properties of Heusler Alloys Fe{sub 2}CrX (X = Al, Ga)

First-principle calculations based on generalized gradient approximation and quasi-harmonic Debye model were executed to analyze the structural, magnetic, elastic, phonon, and thermodynamic properties of Fe{sub 2}CrX (X = Al, Ga) Heusler alloys. The computed lattice parameters concurred well with available experimental and theoretical data. The calculated elastic constants reveal that the Fe{sub 2}CrAl is brittle and Fe{sub 2}CrGa is ductile. The phonon dispersion relation of Fe{sub 2}CrX (X = Al, Ga) are calculated using finite displacement method with a cutoff radius of 5 Å. We likewise explored the thermodynamic properties by utilizing quasi-harmonic Debye model in which bulk modulus, heat capacity, Debye temperature, Grüneisen parameter, and thermal expansion coefficient are resolved at 0–30 Gpa pressure and 0–900 K temperature from the non-equilibrium Gibbs functions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation of Half-Heusler Compounds RhCrZ (Z = P, As, Sb, Sn): A First Principle Study

We have investigated the half-Heusler compounds RhCrZ (Z = P, As, Sb, Sn). The density functional theory (DFT) framework is employed for the study. We have found that structurally these compounds are stable with lattice constants less than 6.00 Å. Elastically, all the compounds are of ductile nature and anisotropic. We have computed their band gaps in both the spin-down and spin-up channels. It is revealed that they have spin-up channels conducting and spin-down channels having a band gap. Furthermore, investigation of optical properties shows that at lower energies compounds are more active.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Study of Half-Heusler Compounds MnVZ (Z = P, As, Sb)

Ab initio study of the half-Heusler compounds MnVZ (Z = P, As, Sb) is performed in the framework of Density Functional Theory (DFT). We have investigated their structural, elastic, mechanical, electronic, magnetic, and optical properties using the full potential linearly augmented plane wave (FP-LAPW) method. The compounds have stable structure with lattice constant in the range 4.90–5.75 Å. The correlation effects are incorporated by performing the GGA + U calculations. The compounds are ductile in nature as indicated by their elastic properties like Cauchy pressure (CP), Pugh’s and Poisson’s ratios. All the three compounds MnVZ (Z = P, As, Sb) are half-metals with small indirect band gaps in the spin-down channels of the values 0.74, 0.30, and 1.29 eV respectively at Γ −X symmetry points. These compounds possess relatively small total magnetic moments of about ≈ 1μ{sub B}. The analysis of optical properties reveals that these compounds are more active at small and high energies and show negligible activity at intermediate energies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Elastic, Thermodynamic, Electronic, and Magnetic Investigations of Full-Heusler Compound Ag{sub 2}CeAl: FP-LAPW Method

Structural, elastic, thermodynamic, electronic, and magnetic properties of the full-Heusler compound Ag{sub 2}CeAl were determined using generalized gradient approximation with exchange-correlation functional GGA (PBEsol) with spin-orbit coupling (SOC) correction. The elastic modulus and their pressure dependence are calculated. From the elastic parameter behavior, it is inferred that this compound is elastically stable and ductile in nature. Through the quasi-harmonic Debye model, in which the phononic effect is considered the effect of pressure P (0 to 50) and temperature T (0 to 1000) on the lattice constant, the elastic parameters, bulk modulus B, heat capacity and thermal expansion α, internal energy U, entropy S, Debye temperature 𝜃{sub D}, Helmholtz free energy A, and Gibbs free energy G are investigated. The thermodynamic properties show that the compound Ag{sub 2}CeAl is a heavy fermion material. The density of state (DOS), magnetic momentum, and band structure are computed, to investigate the magnetic and metallic characteristics. The calculated polarization of the compound is 77.34%. The obtained results are the first predictions of the physical properties for the rare-earth-based (Ce) full-Heusler Ag{sub 2}CeAl.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Insight into Phase Transition, Electronic, Magnetic, Mechanical, and Thermodynamic Properties of TbTe: a DFT Investigation

Theoretical investigation on TbTe for its structural, electronic, magnetic, and thermodynamic stuffs has been carried within density functional theory (DFT) as implemented in WIEN2K code. TbTe was found stable in ferromagnetic phase. The calculated ground-state parameters were found in a good agreement with the experimental data. The compound was found to have a structural stability in cubic B1 (NaCl-type structure) phase, but under the application of high pressure (at 27 GPa), it undergone to B2 (CsCl-type structure) phase of pressure. The second-order elastic constants and mechanical properties like Young’s modulus, Shear modulus, Poisson ratio, Cauchy pressure (C{sub 12}–C{sub 44}), and Pugh’s ratio (B/G) were calculated. The present calculations confirmed the ductile nature of TbTe. Further, the thermodynamic investigations have been carried using quasi-harmonic Debye approximation. We have calculated the pressure and temperature dependence of Debye temperature (𝜃{sub D}), bulk modulus (B), thermal expansion (α), heat capacities (C{sub V}), and entropy (S) in the temperature range of 0 to 1000 K and pressure range of 0 to 25 GPa.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗