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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

NO 2 oxidation reactivity and burning mode of diesel particulates

The NO 2 oxidation kinetics and burning mode for diesel particulate from light-duty and medium-duty engines fueled with either ultra low sulfur diesel or soy methyl ester biodiesel blends have been investigated and are shown to be significantly different from oxidation by O 2 . Oxidation kinetics were measured using a flow-through packed bed microreactor for temperature programmed reactions and isothermal differential pulsed oxidation reactions. The burning mode was evaluated using the same reactor system for flowing BET specific surface area measurements and HR-TEM with fringe analysis to evaluate the nanostructure of the nascent and partially oxidized particulates. The low activation energy measured, specific surface area progression with extent of oxidation, HR-TEM images and difference plots of fringe length and tortuosity paint a consistent picture of higher reactivity for NO 2 , which reacts indiscriminately immediately upon contact with the surface, leading to the Zone I or shrinking core type oxidation. In comparison, O 2 oxidation is shown to have relatively lower reactivity, preferentially attacking highly curved lamella, which are more reactive due to bond strain, and short lamella, which have a higher proportion of more reactive edge sites. Furthermore, this preferential oxidation leads to Zone II type oxidation, where solid phase diffusion of oxygen via pores contributes significantly to slowing the overall oxidation rate, by comparison.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2015

Effect of temperature on the nano/microstructure and mechanical behavior of nanotwinned Ag films

In situ and ex situ annealed nanotwinned (NT) Ag thin films have been investigated by TEM and tensile testing to reveal the thermal stability of the twin boundaries, grain boundaries, dislocation densities, and their respective influence of the macroscopic yield stress. The NT Ag films synthesized by magnetron sputtering form both coherent (CTB, Σ3{111}) and incoherent (ITB, Σ3{112}) twin boundaries that are thermally stable up to 473 K (200 Celsius), i.e., no obvious changes in grain size, twin spacing, and yield stress. In situ TEM observations show the dislocations become mobile at 453 K (180 Celsius) resulting in dislocation annihilation primarily at twin and grain boundaries. Rotation of grains with low-angle grain boundaries was observed during in situ heating, resulting in the growth of columnar grains above 453 K (180 Celsius). However, no noticeable changes in the spacings of CTBs were observed during the entire in situ and ex situ annealing [up to 873 K (600 Celsius)]. The increase in grain size and concomitant decrease in yield stress following annealing at various temperatures can be described by the Hall-Petch relationship, demonstrating that grain size rather than twin spacing is most sensitive to thermal annealing and plays a dominant role in the deformation of NT Ag films.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interfacial Microstructural Evolution and Metallurgical Bonding Mechanisms for IN718 Superalloy Joint Produced by Hot Compressive Bonding

The novel metallurgical joining process for bonding IN718 superalloy was investigated by hot compressive bonding (HCB) process under the deformation temperature range of 1000 °C to 1150 °C and true strains ranging from 0 to 0.5 at a strain rate of 0.001 s{sup −1}. The effect of HCB process parameters on the tensile strength was analyzed. Both the as-deformed and the interfacial microstructures were characterized using the optical microscope, electron backscattered diffraction and transmission electron microscope (TEM) analysis. The results of tensile property revealed that the degree of metallurgical bonding is promoted by increasing deformation temperature and strain. The evolution of the interfacial microstructure showed that the migration of interfacial grain boundary (IGB), which is characterized by discontinuous dynamic recrystallization, is the dominant metallurgical bonding mechanism in the early stages of bonding. TEM analysis indicated that the dislocation density is distributed heterogeneously over both sides of IGB, which is the significant reason for the migration of IGB, during the initial stage of HCB process.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Sb[subscript 2]Te[subscript 3] and Bi[subscript 2]Te[subscript 3] Thin Films Grown by Room-Temperature MBE

Sb{sub 2}Te3 and Bi{sub 2}Te3 thin films were grown on SiO{sub 2} and BaF{sub 2} substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2 nm were alternately deposited at room temperature, and the films were subsequently annealed at 250 C for 2 h. x-Ray diffraction and energy-filtered transmission electron microscopy (TEM) combined with high-accuracy energy-dispersive x-ray spectrometry revealed stoichiometric films, grain sizes of less than 500 nm, and a texture. High-quality in-plane thermoelectric properties were obtained for Sb{sub 2}Te3 films at room temperature, i.e., low charge carrier density (2.6 x 10{sup 19} cm{sup -3}, large thermopower (130 {micro}V K{sup -1}), large charge carrier mobility (402 cm{sup 2} V{sup -1} s{sup -1}), and resulting large power factor (29 {micro}W cm{sup -1} K{sup -2}). Bi{sub 2}Te3 films also showed low charge carrier density (2.7 x 10{sup 19} cm{sup -3}), moderate thermopower (-153 {micro}V K{sup -1}), but very low charge carrier mobility (80 cm{sup 2} V{sup -1} s{sup -1}), yielding low power factor (8 {micro}W cm{sup -1} K{sup -2}). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Formation of Al{sub 15}Mn{sub 3}Si{sub 2} Phase During Solidification of a Novel Al-12%Si-4%Cu-1.2%Mn Heat-Resistant Alloy and Its Thermal Stability

The formation of Al{sub 15}Mn{sub 3}Si{sub 2} phase in Al-12Si-4Cu-1.2Mn (wt.%) alloy during solidification was investigated by adopting CALPHAD method and microstructural observation by optical microscopy, SEM–EDS, TEM–EDS/SAD and XRD analysis; SEM fixed-point observation method was applied to evaluate its thermal stability. As-cast microstructural observation consistently demonstrates the solidification sequence of the studied alloy predicted by phase diagram calculation. Based on the phase diagram calculation, SEM–EDS, TEM–EDS/SAD and XRD analysis, as well as evidences on Al-Si-Mn-Fe compounds from the literature, the primary and eutectic Mn-rich phases with different morphologies in the studied alloy are identified to be Al{sub 15}Mn{sub 3}Si{sub 2} that has a body-centered cubic (BCC) structure with a lattice constant of a = 1.352 nm. SEM fixed-point observation and XRD analysis indicate that Al{sub 15}Mn{sub 3}Si{sub 2} phase has more excellent thermal stability at high temperature than that of CuAl{sub 2} phase and can serve as the major strengthening phase in heat-resistant aluminum alloy that has to face a high-temperature working environment. Results of tension test show that addition of Mn can improve the strength of Al-Si-Cu alloy, especially at elevated temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Grain Refinement by Authigenic Inoculation Inherited from the Medium-Range Order Structure of Ni-Cr-W Superalloy

The combination of liquidus casting and thermal control solidification furnace was applied to obtain a fine-grained ingot. A rapid quenching method and x-ray diffraction measurement were used to investigate the effect of authigenic inoculation on grain refinement. The structure factor S(Q) of liquid Ni-Cr-W superalloy at 1400 °C (Liquidus temperature) and bright-field image of the microstructures quenched from 1400 °C have been measured by the high-temperature x-ray diffractometer and the transmission electron microscopy (TEM), respectively. The results show that a pre-peak exists on a S(Q) curve at the liquidus temperature. The clusters of atom in rapidly quenched microstructures obtained by isothermal heat treatment at 1400 °C were studied using TEM. Meanwhile, the effect of isothermal different temperatures on rapidly quenched microstructures was studied. The results also show that there are only the globular, equiaxed grains distributed in the solidification structure. These particles are inherited from the medium-range order structure, which is beneficial for grain refinement. The normalized work-hardening rate-strain curve indicates the work-hardening rate of fine grain is higher than that of conventional grain at the same temperature and the same deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A Study of Tensile Flow and Work-Hardening Behavior of Alloy 617

The simple power relationship σ = Κε{sub p}{sup n} satisfactorily expresses the tensile flow behavior of many metals and alloys in their uniform plastic strain regime. However, many FCC materials with low stacking fault energy have opposed such power law relationship. Alloy 617, an age-hardenable Ni-based superalloy is also observed not to obey the simple power law relationship neither in its solution-treated nor in its aged conditions. Various flow relationships were used to obtain the best fit for the tensile data, and different relationships were identified for the different aged conditions. The work-hardening rate (θ) demonstrates three distinct regions for all aged conditions, and there is an obvious change in the trend of θ versus σ. In the initial portion, θ decreases rapidly followed by a gradual increase in the second stage and again a decrease in its third stage is perceived in the Alloy 617. These three-stage characteristics are attributed to a commonly known precipitate, γ′: Ni{sub 3}(Ti, Al) which evolves during aging treatment and well recognized under transmission electron microscopy (TEM) observation. TEM results also reveal a slight degree of coarsening in γ′ over aging. The tensile flow and the work-hardening behavior are well correlated with other microstructural evolution during the aging treatments.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High Catalytic Activity of Phenol Photodegradation from Aqueous Solution with Novel Fe-Fe{sub 3}O{sub 4}-GO Nanocomposite

The nano-Fe-Fe{sub 3}O{sub 4}-graphene oxide (GO) composite was successfully synthesized by the precipitation method and followed by chemical reduction using FeCl{sub 3} as iron sources and NaBH{sub 4} as reducing agent. The sample was characterized by XRD, FTIR, TEM, BET, XPS, and VMS. From XRD results, it reveals the formation of both zero valent iron (Fe) and Fe{sub 3}O{sub 4} particles on GO surface. From TEM images, it showed that both Fe{sub 3}O{sub 4}-GO and Fe-Fe{sub 3}O{sub 4}-GO had a small particle size of 10-20 nm. The as-prepared Fe{sub 3}O{sub 4}-GO and Fe-Fe{sub 3}O{sub 4}-GO nanocomposites were tested in the photocatalytic degradation of phenol, which exhibited excellent catalytic activity. After 90 min of reaction under the simulated sunlight irradiation, the conversion reached the value of 87% for Fe-Fe{sub 3}O{sub 4}-GO and 75% for Fe{sub 3}O{sub 4}-GO composite, respectively. The catalyst also showed the high stability. Thus, after three cycles, the conversion of 84% still remained. The high photocatalytic activity of Fe-Fe{sub 3}O{sub 4}-GO composite was rationalized by synergistic effect of Fe° and Fe{sup 2+}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Mechanical Properties of Spray-Formed 7075 Alloy During Retrogression

The mechanical properties, conductivity, microstructure, precipitation behavior and evolution process of elements and phases of spray-formed 7075 alloy during retrogression are studied by the tensile test, electric test, hardness test, transmission electron microscope (TEM), x-ray diffraction (XRD) analysis, electron-dispersive spectroscopy (EDS) and lattice parameter measurements. The results show that the mechanical properties and conductivity of the alloy can be effectively improved when treated at a suitable retrogression temperature and time. According to the TEM observations, XRD analysis, EDS and an accurate measurement of the lattice parameter, the redissolution of elements and precipitated phases can be readily observed. From the optimization selection of the RRA treatment for the 7075 alloy, the regularity of redissolution and precipitation of the elements and phases are evaluated. The ultimate tensile strength, yield strength, hardness, elongation and conductivity of the spray-formed 7075 alloy after preaging at 120 °C for 16 h, retrogression at 200 °C for 8 min and reaging at 120 °C for 24 h are 791, 736 MPa, 181 HBW, 8.5% and 22.6 MS/m, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Development and Mechanical Properties of In Situ Al{sub 3}Ti-Reinforced Nanostructured AA6061 via Mechanical Alloying

Mechanical alloying (MA) was used to disperse 10 wt.% titanium powder in AA6061 powder. The resultant powder was degassed, and differential scanning calorimetry was performed to determine the temperature for formation of titanium aluminide (Al{sub 3}Ti). The MA powder was characterized by field emission scanning electron microscopy, x-ray diffraction (XRD) and transmission electron microscopy (TEM). Subsequently, the MA powder was consolidated by spark plasma sintering (SPS) at 500 °C under a pressure of 50 MPa. XRD and x-ray energy-dispersive spectroscopy of spark plasma sintered compact revealed in situ formation of Al{sub 3}Ti. TEM micrographs of spark plasma sintered sample exhibited Al nanograins (average size 50 nm) in the AA6061 matrix along with the dispersed Al{sub 3}Ti (average size 200 nm). Hardness, yield strength and compressive strength of the SPSed samples were also evaluated and compared with AA6061.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Impact of Hot Bending on the High-Temperature Performance and Hydrogen Damage of 2.25Cr-1Mo-0.25V Steel

The impact of hot bending forming process on the high-temperature mechanical properties and hydrogen damage of 2.25Cr-1Mo-0.25V steel was investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive spectrum (EDS) and the slow strain rate tensile (SSRT) test in high-temperature hydrogen environment. The samples containing hot bending residual influence were extracted from a real hydrogenation reactor shell fabricated through hot bending–welding process. SEM images of the material demonstrated that the density and size of carbides in 2.25Cr-1Mo-0.25V increased after forming. TEM and EDS results revealed that ferrite matrix of the formed material was purified. The mechanical properties measured by SSRT test manifested that 2.25Cr-1Mo-0.25V was softened after forming. Moreover, it was observed that high-temperature hydrogen environment embrittled the material and the susceptibility to hydrogen damage increased after forming. The role of hot bending process on the evolution of mechanical properties and hydrogen damage susceptibility was discussed. Possible mechanism for the impact of hot bending process on the high-temperature hydrogen damage was proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Boron Addition on Creep Strain during Impression Creep of P91 Steel

In an attempt to understand the effect of boron addition on creep deformation behavior under high stress and high temperature in martensitic P91 steel, impression creep tests were carried out on boron-free P91 (P91) and boron-added P91 (P91B) steels. The experimental program consisted of three steps, i.e., characterization of as-received steels by microhardness, optical microscopy (OM), transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and wavelength-dispersive spectroscopy (WDS); impression creep tests at 445 MPa and 625 °C on as-received steels; characterization at deformed plastic zones of impression-crept specimens by microhardness, OM, EBSD, TEM and WDS. Impression creep tests were run till a depth of penetration of 1.8 mm was achieved for both cases which ensured a sufficient plastic zone underneath indenter for subsequent microstructural investigations. Coarsening of M{sub 23}C{sub 6} carbides was observed in P91 steel during high-temperature creep loading, which leads to extensive strain hardening in deformed plastic region, resulting in impaired creep performance. On the contrary, dynamic recrystallization in P91B steel results in formation of small strain-free grains during creep loading which are responsible for increased resistance of the material to shear stresses during an impression creep test.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Application of X-ray Technique to Study the Structure of Ultrafine-Grained Ferritic/Martensitic Steel

In this work, x-ray diffraction and transmission electron microscopy (TEM) analyses have been applied to study the structure of ultrafine-grained (UFG) ferritic/martensitic steel as compared to coarse-grained samples subjected to standard treatment. The x-ray phase analysis of diffraction patterns taken in the “transmission” mode allowed determining the volume fraction and phase composition of particles in the UFG samples. The lattice parameter, the size of coherent scattering domains, the averaged dislocation density, and the fraction of edge and screw dislocations of the ferritic phase in steel were determined according to the diffraction patterns taken in the “reflection” mode. The small-angle x-ray scattering (SAXS) technique was used to study the quantitative characteristics of the size, shape, and distribution of precipitates in the UFG samples. The TEM investigations were performed on the same foils to confirm the results of SAXS. The quantitative evaluations of dispersion and dislocation hardenings in ferritic/martensitic steel were conducted on the basis of the results obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Room temperature deformation mechanisms of alumina particles observed from in situ micro-compression and atomistic simulations.

Aerosol deposition (AD) is a solid-state deposition technology that has been developed to fabricate ceramic coatings nominally at room temperature. Sub-micron ceramic particles accelerated by pressurized gas impact, deform, and consolidate on substrates under vacuum. Ceramic particle consolidation in AD coatings is highly dependent on particle deformation and bonding; these behaviors are not well understood. In this work, atomistic simulations and in situ micro-compressions in the scanning electron microscope, and the transmission electron microscope (TEM) were utilized to investigate fundamental mechanisms responsible for plastic deformation/fracture of particles under applied compression. Results showed that highly defective micron-sized alumina particles, initially containing numerous dislocations or a grain boundary, exhibited no observable shape change before fracture/fragmentation. Simulations and experimental results indicated that particles containing a grain boundary only accommodate low strain energy per unit volume before crack nucleation and propagation. In contrast, nearly defect-free, sub-micron, single crystal alumina particles exhibited plastic deformation and fracture without fragmentation. Dislocation nucleation/motion, significant plastic deformation, and shape change were observed. Simulation and TEM in situ micro-compression results indicated that nearly defect-free particles accommodate high strain energy per unit volume associated with dislocation plasticity before fracture. As a result, the identified deformation mechanisms provide insight into feedstock design for AD.

36 MATERIALS SCIENCE↗
DOE OSTI2022

On the Phase with an Unreported Ternary Composition Found in the P-Pt-Rh System

This work reports a ternary structure in the P-Pt-Rh system, which has a composition not reported in the literature. The structure formed in the Pt-6 wt.% Rh alloy which was partially melted in a P-enriched CO environment near 1000 °C isothermally and non-isothermally as part of the type B thermocouple assembly. A composition and a crystal structure of this phase were investigated by utilizing SEM, EPMA, XRD and TEM techniques to discuss the potential of this structure being a true ternary phase. The EPMA indicated chemistries of the ternary structure from both isothermal and non-isothermal samples were about 23P-52Pt-25Rh (at.%) and, 22P-54Pt-24Rh (at.%) respectively. TEM diffraction patterns identified this ternary structure to be crystalline with a complex non-cubic structure, and confirmed it was not amorphous. Finally, by superimposing the compositions in the ternary phase diagram, it was concluded this phase was not extensions of any binary phases known in the respective binary systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Development of Fe-9Cr Alloy via High-Energy Ball Milling and Spark Plasma Sintering

Iron and chromium powders were mixed and mechanically alloyed via high-energy ball milling for different time durations (2–20 h) to produce an alloy powder with a nominal composition of Fe-9Cr (wt.%). The milled Fe-9Cr powders were analyzed using scanning electron microscopy (SEM), x-ray diffraction (XRD) and transmission electron microscopy (TEM) to understand the impact of ball milling (BM) time on the characteristics of the milled powder. The optimized milled powder samples were then consolidated via spark plasma sintering (SPS) for different dwell times and temperatures. The density of consolidated samples was found to reach a maximum of 98%. Microstructural characterization of the SPS samples were performed using XRD, SEM, TEM and electron backscatter diffraction. This study highlights the principles and importance of high-energy BM and SPS of Fe-9Cr model alloy for the future development of more complex oxide dispersion-strengthened alloys for various applications including advanced nuclear reactor applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Experimental investigation of the ordering pathway in a Ni-33 at.%Cr alloy

The present study involves a detailed experimental investigation of the concurrent compositional clustering and long-range ordering tendencies in a Ni-33 at.%Cr alloy, carried out by coupling synchrotron-based X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT). Synchrotron-based XRD results clearly exhibited progressively increasing lattice contraction in the matrix with increasing isothermal aging time, at 475 degrees C, eventually leading to the development of long-range ordering (LRO) of the Pt2Mo-type. Detailed TEM and APT investigations revealed that this LRO in the matrix is manifested in the form of nanometer-scale ordered domains, and the spatial distribution, size, morphology and compositional evolution of these domains have been carefully investigated. Here, the APT results also revealed the early stages of compositional clustering prior to the onset of long-range ordering in this alloy and such compositional clustering can potentially be correlated to the lattice contraction and previously proposed short-range ordering tendencies.

36 MATERIALS SCIENCE↗