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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Additive manufacturing of high-strength multiphase nanostructures in the binary Ni–Nb system for the discovery of new types of superalloys

Abstract Ni-based superalloys have been studied extensively due to their impressive mechanical properties, including strength and creep resistance at high temperatures. Growing interest surrounding additive manufacturing (AM) methods has led to recent investigations of alloys that are traditionally difficult to process, including Ni-based superalloys. Recent work has shown that AM methods enable high-throughput materials discovery and optimization of difficult- or impractical-to-process alloys, including those with high or even majority refractory element compositions. This work focuses on AM-enabled investigations of composition-dependent mechanical and microstructural properties for Ni–Nb binary alloys. Specifically, we report on the mechanical behavior of compositionally-graded Ni x Nb 1− x and uniform composition Ni 59.5 Nb 40.5 specimens made with AM. The AM fabrication process resulted in extraordinarily high strength, attributed to the formation of a dual-phase microstructure consisting of δ-Ni 3 Nb and µ-Ni 6 Nb 7 intermetallic compounds with nanostructured and multimodal grain size and eutectic lamellar spacing. Graphic Abstract

Jones, M. R.↗
DOE OSTI2021

Deep Learning-Based Hardness Prediction of Novel Refractory High-Entropy Alloys with Experimental Validation

Hardness is an essential property in the design of refractory high entropy alloys (RHEAs). This study shows how a neural network (NN) model can be used to predict the hardness of a RHEA, for the first time. We predicted the hardness of several alloys, including the novel C0.1Cr3Mo11.9Nb20Re15Ta30W20 using the NN model. The hardness predicted from the NN model was consistent with the available experimental results. The NN model prediction of C0.1Cr3Mo11.9Nb20Re15Ta30W20 was verified by experimentally synthesizing and investigating its microstructure properties and hardness. This model provides an alternative route to determine the Vickers hardness of RHEAs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Dual-Phase Heat Treatment on Microstructure and Mechanical Properties of S135 High-Strength Drill Pipe Steel

Effect of dual-phase heat treatment (DPHT) on microstructure and mechanical properties of S135 high-strength drill pipe steel was studied by means of optical microscope, scanning electron microscope and mechanical property testing. The results show that the ferrite–martensite dual-phase microstructures were obtained at 760-800 °C. With increase in DPHT temperature, the volume fraction of martensite increases and the ferrite decreases. When the DPHT temperature is low, martensite is distributed as an island on the ferrite matrix, and ferrite is distributed as an island on the martensite matrix when the DPHT temperature is high. The hardness and strength of the steel increase, the plasticity and toughness decrease, the steel changes from ductile fracture to brittle fracture and the micro-fracture morphology changes from dimple to cleavage with increase in DPHT temperature. The strain hardening exponent of the as-received steel shows one ‘n’ value, but exhibits two ‘n’ values after DPHT. When the DPHT temperature is 750 °C, the relative content of martensite in the duplex structure is 15-20%, and the impact energy of the steel is similar to that of the as-received S135 drill pipe steel, and the strength is increased by about 15%. Micropores and micro-cracks on the subsurface of tensile fracture surface are mainly formed at the martensite/ferrite phase boundary or in the martensite slit.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructural diversity and digestion yields of select bituminous and subbituminous coals as raw material candidates for carbon fiber precursor production

Here, this work investigates the use of coals as raw materials for carbon fiber precursor production as a new alternative to coal utilization. Coal being a highly complex and heterogeneous material with different macerals and minerals complicates this task. Extensive microstructural characterization as well as preliminary digestion studies are performed on three bituminous coals (Herrin and Springfield from the Illinois Basin and the Blue Gem from the Central Appalachians) and one subbituminous coal from the Powder River Basin (Monarch), as raw material candidates. The subbituminous coal was richer in oxygen, lower in sulfur, and had a higher volatile matter yield. Microstructural investigations were performed using X-ray diffraction, X-ray/neutron computed tomography, scanning electron microscopy with energy dispersive spectroscopy, and petrology. Mild solvent extraction studies were conducted using creosote and decant oil as solvents in microreactors. The extraction yield was sensitive to temperature and time (350 to 450 °C between 30 and 120 mins.) for both creosote and decant oil digestions. While the Blue Gem coal had more desirable microstructural properties with less mineral content and cleaner macerals, it had the lowest coal conversion to quinoline soluble ‘liquid’ (of the bituminous coals). The lower coal conversion yield was hypothesized to be connected to the lack of FeS2 which could act as a catalyst when Fe is liberated from the structure under solvent extraction conditions. The Herrin and Springfield coals revealed similar microstructures and coal conversion efficiencies (higher than Blue Gem). These coals were the most promising candidates for further examination from this first approximations study. The subbituminous Monarch coal, however, was deemed less suitable due to poor coal conversion and less desirable microstructures. Additionally, the presented results with combined microstructural data from multiple length scales established a framework necessary for a first approximations study in this new coal utilization approach.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2018

Microstructures and mechanical properties of the welded AA5182/HC340LA joint by magnetic pulse welding

Highlights: • The magnetic pulse welding of 5× aluminum alloy with high strength steel is performed. • The microstructure evolution of welding interface under different parameters is investigated. • The intermediate layer is characterized by high-resolution transmission electron microscope and electron diffraction pattern. - Abstract: Magnetic pulse welding (MPW) is an innovative joining technology for dissimilar materials. The MPW with high joining qualities could be realized between high strength steel and 5× aluminum alloys. In this work, the MPW joints between aluminum alloy (AA 5182) sheet and high-strength low alloy steel (HC340LA) sheet were prepared under various discharge energies. The mechanical properties and microstructure observations were employed to evaluate the joint performance. Results showed that a lower discharge voltage tended to cause joints with poor quality. When the discharge energy increased, the failure position gradually changed from the weld zone to the weaker base metal (Al) during quasi-static tensile tests. In addition, the effect of discharge energies on microstructure evolution in the intermediate layer was revealed by high-resolution transmission electron microscopy (HRTEM) and scanning electron microscope (SEM). Atomic-scale diffusion was found to be the mainly welding mechanism of the Al/Fe joint. The intermetallic compound (IMC) FeAl{sub 2} and ultra-fine grains (UFG) were found in the intermediate layer under high discharge energy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Heat Treatment on Microstructure and Magnetic Properties of Ce-Doped NdFeB Ribbons

The substitution for Nd by abundant element cerium (Ce) is a practical way for the comprehensive utilization of rare earth resources in NdFeB permanent magnets. In this letter, we have prepared the Ce-doped NdFeB ribbons and conventional NdFeB ribbons by melt quenching method and investigated the effects of heat treatment on the crystallization behavior, microstructure, and magnetic properties of the alloy. The results show that: (1) The crystallization behavior and the microstructural changes of the (Nd,Ce)FeB magnets are similar to the conventional NdFeB magnet when heat treatment. In addition, the Ce{sub 2}Fe{sub 14}B phase has a significant effect on the properties of the whole magnets. (2)The NdFeB phase and CeFeB phase are relatively close to each other after being precipitated from the amorphous phase. The coupling effect between the two phases is strong enough to weaken the effect of the addition of Ce and making the properties of the NdFeB magnets to not reduce too much after adding Ce.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Relationship between laser energy input, microstructures and magnetic properties of selective laser melted Fe-6.9%wt Si soft magnets

Highlights: • Effect of laser energy input on magnetic properties of SLM Fe-6.9%wt.Si is described; • Magnetic properties can be described as function of as-built microstructure after stress-relief post-treatment; • Samples with density >99% and strong crystallographic texture along BD have the best magnetic properties; • At very high laser energy, a strong cube texture forms that deteriorates the magnetic properties. - Abstract: Selective Laser Melting (SLM), a powder-bed Additive Manufacturing technology, can be used in combination with high temperature post-annealing to produce high-silicon steel parts characterised by quasi-static magnetic properties comparable to those of commercial electrical steel. However, the role of the as-built microstructure on the magnetic properties is still unexplored. Therefore, in this study the effect of the energy input of the processing laser on the magnetic properties of the material is investigated. The magnetic properties are determined for 4 mm-high rings obtained using three laser energy input values that provide a good compromise in terms of porosity and crack formation. The best magnetic properties are obtained for the rings built using a value of energy input that produces a strong fibrous crystallographic texture, in which one of the crystallographic <001> axes is preferentially aligned along the build direction. Whether the magnetic properties change with sample direction as a result of the crystallographic texture will be the subject of future research.

36 MATERIALS SCIENCE↗
DOE OSTI2016

“Additive Manufacturing: Building the Pathway Towards Process and Material Qualification”

The potential benefits of metal additive manufacturing, as compared with more traditional, subtractive-only approaches, has created excitement within design circles seeking to take advantage of the ability to build and repair complex shapes, to integrate or consolidate multiple parts and minimize joining concerns, and to locally tailor material properties to increase functionality. Tempering the excitement of designers, however, has been concerns with the material deposited by the process. It is not enough for a part to ‘look’ right from a geometric perspective. Rather, the metallurgical aspects associated with the material being deposited must ‘look’ and ‘behave’ correctly along with the aforementioned geometric accuracy. Finally, without elucidation of the connections between processing, microstructure, properties, and performance from a materials science perspective, metal additive manufacturing will not realize its potential to change the manufacturing world for property and performance-critical engineering applications.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Quantifying Microstructure Variability in Laser Powder Bed Fusion 316 L Stainless Steel Microstructures with Spatial Statistics

Here, we have explored data-driven methods for material microstructure quantification that improve sensitivity to microstructural changes compared to traditional approaches. The methods integrate multiple microstructural properties, including grain morphology, crystallographic orientation, and material phase information. The simpler method employs maps of the Euclidean distance transformation metric to evaluate the morphology of grain boundary networks. The more intensive approach employs generalized spherical harmonic mapping for crystallographic orientations, per-pixel phase information, and a variational auto-encoder for dimensionality reduction and results in a multidimensional clustering of by microstructure similarity. Applied to an experimental dataset of additively manufactured steel, both methods detected slight variations in samples produced under nominally identical processing conditions. Both methods were able to distinguish between samples from multiple (nominally identical) builds, while the generalized spherical harmonics-based method could additionally cluster data samples rotated at two orientations on the build plate. The improved sensitivity of the methods, demonstrated through comparison with traditional microstructure characterization techniques, offers advantages for microstructure quantification and comparisons in advanced manufacturing applications.

SS316L↗
DOE OSTI2014

Annealing effect for SnS thin films prepared by high-vacuum evaporation

Thin films of SnS are deposited onto molybdenum-coated soda lime glass substrates using the high-vacuum evaporation technique at a substrate temperature of 300 °C. The as-deposited SnS layers are then annealed in three different media: (1) H{sub 2}S, (2) argon, and (3) vacuum, for different periods and temperatures to study the changes in the microstructural properties of the layers and to prepare single-phase SnS photoabsorber films. It is found that annealing the layers in H{sub 2}S at 400 °C changes the stoichiometry of the as-deposited SnS films and leads to the formation of a dominant SnS{sub 2} phase. Annealing in an argon atmosphere for 1 h, however, causes no deviations in the composition of the SnS films, though the surface morphology of the annealed SnS layers changes significantly as a result of a 2 h annealing process. The crystalline structure, surface morphology, and photosensitivity of the as-deposited SnS films improves significantly as the result of annealing in vacuum, and the vacuum-annealed films are found to exhibit promising properties for fabricating complete solar cells based on these single-phase SnS photoabsorber layers.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructure and mechanical properties of Ti-35Nb-6Ta alloy after thermomechanical treatment

The influence of thermo-mechanical treatment on microstructure and mechanical properties of T-35Nb-6Ta has been studied. The thermo-mechanical treatment was chosen to correspond to the production of wire with suitable mechanical properties for dental implants. After casting the alloy was hot forged (700-900 Degree-Sign C), solution treated (850 Degree-Sign C/30 min, water quenched) and cold swaged (reductions up to 91%). The annealing (700 Degree-Sign C/3 h/furnace) or aging (450 Degree-Sign C/8 h/furnace) was used as final heat treatment. The microstructure was studied by using light microscopy, scanning electron microscopy, transmission electron microscopy and XRD analysis. Cold swaging introduces microstructure consisting of highly deformed {beta}-phase grains with dislocation tangles and twins, which ensures high tensile strength about 820 MPa, low Young's modulus ({approx} 50 GPa) and good ductility {approx} 10%. Subsequent aging increases tensile strength (1000 MPa) as well as Young's modulus (75 GPa) without diminishing ductility. Annealing at 700 Degree-Sign C slightly decreases tensile strength (730 MPa) and increases the ductility and Young's modulus (17% and 62 GPa respectively). The mechanical properties attained recommend the thermo-mechanical treatment for production of wires for dental implants. - Highlights: Black-Right-Pointing-Pointer Ti35Nb6Ta alloy prepared via arc melting. Black-Right-Pointing-Pointer Thermo mechanical treatment. Black-Right-Pointing-Pointer Microstructural changes. Black-Right-Pointing-Pointer Mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis and Structural Characterization of Sb-Doped TiFe{sub 2}Sn Heusler Compounds

Ternary Heusler compounds form a numerous class of intermetallics, which include two families with general compositions ABC and AB{sub 2}C, usually referred to as half- and full-Heusler compounds, respectively. Given their tunable electronic properties, made possible by adjusting the chemical composition, these materials are currently considered for the possible use in sustainable technologies such as solar energy and thermoelectric conversion. According to theoretical predictions, Sb substitution in the TiFe{sub 2}Sn full-Heusler compound is thought to yield band structure modifications that should enhance the thermoelectric power factor. In this work, we tested the phase stability and the structural and microstructural properties of such heavily doped compounds. We synthesized polycrystalline TiFe{sub 2}Sn{sub 1−x}Sb{sub x} samples, with x = 0, 0.1, 0.2 and 1.0 by arc melting, followed by an annealing treatment. The structural characterization, performed by x-ray powder diffraction and microscopy analyses, confirmed the formation of the pseudo-ternary Heusler structure (cF16, Fm-3m, prototype: MnCu{sub 2}Al) in all samples, with only few percent amounts of secondary phases and only slight deviations from nominal stoichiometry. With increasing Sb substitution, we found a steady decrease in the lattice parameter, confirming that the replacement takes place at the Sn site. Quite unusually, the as-cast samples exhibited a higher lattice contraction than the annealed ones. The fully substituted x = 1.0 compound, again adopting the MnCu{sub 2}Al structure, does not form as stoichiometric phase and turned out to be strongly Fe deficient. The physical behavior at room temperature indicated that annealing with increasing temperature is beneficial for electrical and thermoelectrical transport. Moreover, we measured a slight improvement in electrical and thermoelectrical properties in the x = 0.1 sample and a suppression in the x = 0.2 sample, as compared to the undoped x = 0 sample.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Plan for Post-Irradiation Examination of Zion Reactor Pressure Vessel Beltline Materials

The reactor pressure vessel (RPV) is a potentially life-limiting component in light-water reactors (LWR) because replacement of the RPV is not considered a viable option. Researchers studying the effects of radiation on RPV materials have long been interested in evaluating service-irradiated materials to assess currently available models for predicting radiation embrittlement of RPV steels. The decommissioning of the Zion Unit 1 NPP in Zion, Illinois presents a unique opportunity for characterization of an actual reactor pressure vessel (RPV) material after inservice degradation. The main interests in this case are the belt-line weld and base metals. Through-RPV wall thickness attenuation and chemical composition distributions are the obvious objectives of this characterization program. However, it also provides an opportunity to examine the inservice degradation and its comparison with currently available models for prediction of radiation embrittlement of RPV steels. All of these efforts will provide a better understanding of materials degradation and other issues associated with extending the lifetime of existing NPPs beyond 60 years of service. The primary foci are the Linde 80 flux, wire heat 72105 (WF-70) circumferential belt-line weld and the A533B-1 base metal from the intermediate shell harvested from a region of peak fluence (0.7 x 10{sup 19} n/cm{sup 2}, E > 1.0 MeV) on the internal surface of the Zion Unit 1 vessel. Following determination of the through-thickness chemical composition, Charpy impact, fracture toughness, tensile, and hardness testing will be being performed to characterize the through-thickness mechanical properties of the base metal and belt-line-weld materials. In addition to mechanical properties, microstructural characterizations will be performed using various techniques, including Atom Probe Tomography, Small Angle Neutron Scattering, and Positron Annihilation Spectroscopy.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2018

Correlation between microstructures and mechanical properties of cryorolled CuNiSi alloys with Cr and Zr alloying

Highlights: • Annihilation of dislocations was suppressed by Cr alloying to CuNiSi alloys. • Cr alloying to CuNiSi alloys hinders the kinetics and refines precipitates. • Zr alloying to CuNiSi alloys promotes the growth and kinetics of precipitates. • The mechanical properties were quantitatively related to the microstructures. - Abstract: Due to their high strength and high electrical conductivity, CuNiSi system alloys are widely used as lead frames and connectors. In this work, CuNiSi alloys alloyed with Cr and Zr were rolled at liquid nitrogen temperature and subjected to various aging treatments. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) analysis showed that in addition to forming Cr{sub 3}Si and Ni{sub 2}SiZr particles, elemental Cr and Zr distributed evenly in the matrix. Ni and Si segregated at the interface between the particles and matrix to form Ni{sub 2}Si precipitates. During the aging process, Cr alloying increased the hardness while slightly reducing the electrical conductivity of the alloy. This was ascribed to the refined precipitates and hindered precipitation kinetics. Zr alloying promoted both the precipitate growth and the precipitation kinetics of the CuNiSi alloys, while decreasing their hardness and enhancing their electrical conductivity. According to the results of the synchrotron X-ray diffraction (XRD) analysis, Cr alloying increased the dislocation density of CuNiSi alloys and suppressed the annihilation of dislocations during aging. This promoted strength through work hardening. Compared to CuNiSi alloys aged at 723 K for 2 h, the ultimate tensile strength of the alloys obtained after Cr alloying using a two-step rolling aging process was increased by 154 MPa and their electrical conductivity was increased by 4.8% International Annealed Copper Standard (IACS).

36 MATERIALS SCIENCE↗
DOE OSTI2024

The role of annealing and grain boundary controls on the mechanical properties of limestones and marbles

Chemical and mechanical processes are coupled in many geological and geochemical environments. Reactive processes anneal defects and restructure grain boundaries, modifying their elastic properties, levels of internal friction, wave propagation rates and fracture behaviors. The nature of these changes is, however, contingent on the initial state of the rock. Here, in this study, impulse excitation was used to measure changes in mechanical properties as a function of dry and steam heating time at 300 °C for three carbonate rocks: Carrara marble, Carthage marble (Burlington Limestone), and Texas Cream limestone (Edwards limestone), with initial porosities of about 1 %, 3 %, and 27 %, respectively. Frequency-dependent phenomena along with mineral recrystallization were observed. This was coupled with small-angle X-ray and neutron scattering analysis to determine the relationship between changes in bulk mechanical and microstructural properties. An observed decrease in both the Young's and shear moduli in the experimental limestones as a function of heating time reflects and quantifies a reduction in the stiffness of the rock due to annealing. The internal friction of the samples first increases then decreases with reaction time, reflecting defect annealing, but this was balanced against grain boundary dissolution apparently driven by condensation of steam in the confined grain-boundary environment. This suggests an increase in the boiling point under confinement leading to dissolution, increased porosity and widening of the grain boundaries. In addition, comparison of small-angle X-ray and neutron scattering results suggests that it is inappropriate to assume that pores are empty for quantitative analysis of typical small-angle scattering samples.

58 GEOSCIENCES↗
DOE OSTI2013

Effects of ruthenium seed layer on the microstructure and spin dynamics of thin permalloy films

The spin dynamics and microstructure properties of a sputtered 12 nm Ni{sub 81}Fe{sub 19} thin film have been enhanced by the use of a ruthenium seed layer. Both the ferromagnetic resonance field and linewidth are enhanced dramatically as the thickness of ruthenium seed layer is increased. The surface anisotropy energy constant can also be largely tailored from 0.06 to 0.96 erg/cm{sup -2} by changing the seed layer thickness. The changes to the dynamics magnetization properties are caused by both ruthenium seed layer induced changes in the Ni{sub 81}Fe{sub 19} structure properties and surface topography properties. Roughness induced inhomogeneous linewidth broadening is also seen. The damping constant is highly tunable via the ruthenium thickness. This approach can be used to tailor both the structure and spin dynamic properties of thin Ni{sub 81}Fe{sub 19} films over a wide range. And it may benefit the applications of spin dynamics and spin current based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermo-Oxidative Aging of LDPE/Stearoyl Chloride-Grafted Cellulose Nanocrystals Blown Films

The effect of the incorporation of pristine and stearoyl chloride grafted CNCs on the chemical, mechanical, thermal and microstructural properties, during the thermo-oxidative aging, of LDPE blown films at 60 °C was studied. The success of the pristine CNCs grafting was assessed by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Thermal-gravimetric analysis (TGA), Atomic Force Spectroscopy (AFM) and contact angle measurements. The results show that chemical modification decreases both, the CNCs thermal stability and the polar component of surface energy, i.e. increases the nanocrystals hydrophobicity. Also, it was found that neither CNCs crystalline structure nor its dimensions changed with grafting. The changes on the blown film properties during thermo-oxidative aging were monitored using FT-IR, DSC, DRX and tensile testing. It was found that the CNCs catalyzed the production of carboxylic acids as a final degradation by-product, whereas the CNC-g-C{sub 18} inhibits its formation, i.e. in presence of CNCs grafted with stearoyl chloride the catalytic effect attributed to the pristine CNCs was partially inhibited. The DSC, DRX and tensile testing results show the microstructural arrangements due to the annealing and the chains oxidation predominated during the first 30 days of aging and then chain scissions prevail. These findings suggest an analogous reduction in molecular weight at the end thermo-oxidative aging. In addition, the presence of a high concentration of carboxylic acid and the drop in molecular weight after LDPE aging will facilitate the biodegradation of these oxo-degradable films.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ab initio study of the structure and properties of amorphous silicon hydride from accelerated molecular dynamics simulations

This paper presents a large-scale ab initio simulation study of amorphous silicon hydride (a-Si 1-x H x ) with an emphasis on the structure and properties of the material across a range of hydrogen concentration by combining accelerated molecular dynamics (MD) simulations with first-principles density-functional calculations. The accelerated MD scheme relied on classical metadynamics, which enabled the development of 2500+ high-quality structural models of a-Si 1-x H x , with system sizes ranging from 150 to 6000 atoms and hydrogen concentrations vary from 6 to 20 at. %. The resulting amorphous networks were found to be completely free from any coordination defects and that they all exhibited a pristine band-gap in their electronic spectrum. The microstructural properties of hydrogen distributions were examined with an emphasis on the presence of isolated and clustered environments of hydrogen atoms. The results were compared with experimental data obtained from X-ray diffraction, infrared spectroscopy and nuclear magnetic resonance studies.

36 MATERIALS SCIENCE↗