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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Crystallization dynamics in glass-forming systems

Crystallization under far-from-equilibrium conditions is investigated for two different scenarios: crystallization of the metallic glass alloy Cu 50 Zr 50 and solidification of a transparent organic compound, o-terphenyl. For Cu 50 Zr 50 , crystallization kinetics are quanti ed through a new procedure that directly fits thermal analysis data to the commonly utilized JMAK model. The phase evolution during crystallization is quantified through in-situ measurements (HEXRD, DSC) and ex-situ microstructural analysis (TEM, HRTEM). The influence of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined. For o-terphenyl, the relationship between crystal growth velocity and interface undercooling is systematically studied via directional solidification.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Characterization of basin concrete in support of structural integrity demonstration for extended storage

Concrete core samples from C basin were characterized through material testing and analysis to verify the design inputs for structural analysis of the L Basin and to evaluate the type and extent of changes in the material condition of the concrete under extended service for fuel storage. To avoid the impact on operations, core samples were not collected from L area, but rather, several concrete core samples were taken from the C Basin prior to its closure. C basin was selected due to its similar environmental exposure and service history compared to L Basin. The microstructure and chemical composition of the concrete exposed to the water was profiled from the water surface into the wall to evaluate the impact and extent of exposure. No significant leaching of concrete components was observed. Ingress of carbonation or deleterious species was determined to be insignificant. No evidence of alkali-silica reactions (ASR) was observed. Ettringite was observed to form throughout the structure (in air voids or pores); however, the sulfur content was measured to be consistent with the initial concrete that was used to construct the facility. Similar ettringite trends were observed in the interior segments of the core samples. The compressive strength of the concrete at the mid-wall of the basin was measured, and similar microstructural analysis was conducted on these materials post compression testing. The microstructure was determined to be similar to near-surface segments of the core samples. The average strength was 4148 psi, which is well-above the design strength of 2500 psi. The analyses showed that phase alterations and minor cracking in a microstructure did not affect the design specification for the concrete.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Effect of nano-SiO{sub 2} particles and curing time on development of fiber-matrix bond properties and microstructure of ultra-high strength concrete

Bond properties between fibers and cementitious matrix have significant effect on the mechanical behavior of composite materials. In this study, the development of steel fiber-matrix interfacial bond properties in ultra-high strength concrete (UHSC) proportioned with nano-SiO{sub 2} varying between 0 and 2%, by mass of cementitious materials, was investigated. A statistical model relating either bond strength or pullout energy to curing time and nano-SiO{sub 2} content was proposed by using the response surface methodology. Mercury intrusion porosimetry (MIP) and backscatter scanning electron microscopy (BSEM) were used to characterize the microstructure of the matrix and the fiber-matrix interface, respectively. Micro-hardness around the embedded fiber and hydration products of the matrix were evaluated as well. Test results indicated that the optimal nano-SiO{sub 2} dosage was 1% in terms of the bond properties and the microstructure. The proposed quadratic model efficiently predicted the bond strength and pullout energy with consideration of curing time and nano-SiO{sub 2} content. The improvement in bond properties associated with nano-silica was correlated with denser matrix and/or interface and stronger bond and greater strength of hydration products based on microstructural analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Fabrication and thermophysical property characterization of UN/U 3 Si 2 composite fuel forms

High uranium density composite fuels composed of UN and U 3 Si 2 have been fabricated using a liquid phase sintering route at temperatures between 1873 K and 1973 K and spanning compositions of 10 vol% to 40 vol% U 3 Si 2 . Microstructural analysis and phase characterization revealed the formation of an U-Si-N phase of unknown structure. Microcracking was observed in the U-Si portion of the composite microstructure that likely originates from the mismatched coefficient of thermal expansion between the UN and U 3 Si 2 leading to stresses on heating and cooling of the composite. Thermal expansion coefficient, thermal diffusivity, and thermal conductivity were characterized for each of the compositions as a function of temperature to 1673 K. Hysteresis is observed in the thermal diffusivity for the 20 vol% through 40 vol% specimens between room temperature and 1273 K, which is attributed to the microcracking in the U-Si phase. Thermal conductivity of the composites was modeled using the MOOSE framework based on the collected microstructure data. In conclusion, the impact of irradiation on thermal conductivity was also simulated for this class of composite materials.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

An investigation of the microstructure and ductility of annealed cold-rolled tungsten

Tungsten is notoriously brittle metal at room temperature. Furthermore, contrary to most metals, plastic deformation increases ductility and recrystallization decreases ductility of tungsten. The fundamentals that govern this behavior have challenged academia and industry for decades. This paper focuses on understanding the controlling factors of ductility through a systematic investigation of the changes in microstructure and mechanical properties of cold-rolled tungsten that occur during annealing. Cold-rolled tungsten samples were annealed at temperatures up to 1400 °C, and mechanical testing and microstructural analysis was performed before and after annealing. Furthermore, a dislocation mobility model based on the Orowan equation was applied. The mechanisms of deformation are discussed within the context of deformed and annealed microstructures. The high fraction of low angle grain boundaries and high density of edge dislocations were found to be the most important factors for ductility. Although there were gradual changes in microstructure and mechanical properties, the ductility of cold-rolled tungsten was maintained up to 1300 °C. The material recrystallized when annealed above this temperature, had no ductility, and suffered brittle fracture. Microstructural characterizations of the as-rolled material revealed a typical BCC texture, with grains elongated in rolling direction and a large amount of edge dislocations and low angle grain boundaries. The level of texturing and the fraction of low angle grain boundaries diminished after recrystallization. It was found that, compared to the recrystallized material, as-rolled tungsten can accommodate over 7 orders of magnitude higher deformation velocity due to the high density of edge dislocations.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Three-dimensional analysis by serial sectioning of cubic zirconia sinters

Three-dimensional electron backscatter diffraction technique was used for the characterization of grain boundary geometry and pore morphology in cubic zirconia. A set of three samples composed of cubic yttria stabilized zirconia, sintered under different conditions was investigated. Analysis of grain boundaries and pore structure was carried out in a dual-beam scanning electron microscope. For each sample, a volume of 15·10{sup 3} μm{sup 3} was investigated. The results of three-dimensional microstructure analysis were compared to the results derived from regular, two-dimensional maps of the area of 2500 µm{sup 2}. Based on two-dimensional and three-dimensional data the average grain diameter, number of grains, average number of neighbors and porosity were calculated. The average grain diameter varied in the range from 2.39 µm to 2.91 µm and from 3.00 µm to 3.79 µm, while the level of porosity varied in the range from 1.22% to 1.77% and from 1.30% to 5.61% for two-dimensional and three-dimensional data, respectively. The analysis of grain boundary networks revealed a strong dependence between grain boundary density and sample preparation parameters. The parameters of the sintering process affected also the size and distribution of pores. The comparison of the results of 2D and 3D materials characterization revealed significant differences in the values of calculated microstructure parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of X80 and X100 Microalloyed Pipeline Steel Using Quantitative X-ray Diffraction

Quantitative X-ray diffraction characterization of four (4) X80 and three (3) X100 microalloyed steels was undertaken. The effect of through-thickness position, processing parameters, and composition on the measured crystallite size, microstrain, and J index (relative magnitude of crystallographic texture) was determined. Microstructure analysis using optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron-backscattered diffraction was also undertaken. The measured value of microstrain increased with increasing alloy content and decreasing cooling interrupt temperature. Microstructural features corresponding to crystallite size in the X80 steels were both above and below the detection limit for quantitative X-ray diffraction. The X100 steels consistently exhibited microstructure features below the crystallite size detection limit. The yield stress of each steel increased with increasing microstrain. The increase in microstrain from X80 to X100 is also associated with a change in microstructure from predominantly polygonal ferrite to bainitic ferrite.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Correlation Between Microstructure and In-Field Performance of Zr-Added REBCO Coated Conductors Made by Advanced MOCVD

In this paper, we present correlation features between critical current density (J c ) and microstructural characteristics of Zr-added (0, 5, and 15 mol.%) REBa 2 Cu 3 O 7-x (REBCO and RE = rare earth) coated conductors fabricated by the novel advanced metal organic chemical vapor deposition technique. The J c along the tape normal (~ B || c-axis) measured by a vibrating sample magnetometer at 30 and 65 K and magnetic flux density range of 0-14 T was used for qualitative comparison of different Zr-added REBCO tapes. It is found that tapes with enhanced in-field J c exhibit a rise of critical current (plateau or fishtail effect) at magnetic flux density 1-8 T and temperatures 65 K. The TEM microstructure analysis indicates that the plateau effect is not the intrinsic property of REBCO matrix but depends on size distribution and density of BaZrO 3 (BZO) self-assembled nanocolumns. Two types of BZO microstructures have been identified: one with uniform BZO diameter 4-7 nm, whereas some films exhibit bottle-shaped BZO nanocolumns with alternating wide and narrow sections, 7-13 and 4-6 nm, respectively. The non-uniform shape and broad size distribution of BZO nanocolumns are correlated to more vortex pinning strength and matching field.

2G high-temperature superconductor (2GHTS)↗
DOE OSTI2016

Nano-scale mechanical behavior of uranium silicide compounds

Uranium silicide compounds exhibit a range of attractive material properties for nuclear fuel applications, but little is known regarding their mechanical behavior. The structure of nuclear fuels at high burnup can prove to be especially difficult given the significant changes in both chemistry and microstructure caused by fission products. Nano-indentation appears to be a valuable addition to post irradiation examination. The present focus is assessment of the room temperature modulus and hardness of U{sub 3}Si{sub 2}, U{sub 3}Si{sub 5} and USi materials. Each of the compositions under investigation was synthesized via arc melting of the pure metals in an Ar atmosphere using a titanium getter to remove O{sub 2} contamination. The resulting pellets following milling and sintering of the arc melted material were between 96 and 98% of density. Coupling different techniques (SEM and Chemical Analysis), microstructural investigations of the samples has been performed. Preliminary nano-mechanical response of U-Si fuel materials has been demonstrated, on a Hysitron Tribo-indenter which will impact the ability to design advanced fuel materials for enhanced high temperature performance.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Crack mitigation and wear performance of high-strength steel coatings deposited by high-speed laser cladding

This article investigates the fabrication of defect-free Rockit® 606, a high‑carbon, vanadium- and chromium-enriched precipitation-hardening martensitic steel coating, using high-speed laser cladding (HSLC). Compared to conventional laser cladding, HSLC offers higher deposition efficiency, improved coating quality, minimal thermal distortion, and a reduced heat-affected zone. Various HSLC parameters—including laser power, travel speed, powder feed rate, and overlap distance—were optimized to achieve superior coating properties. Microstructural analysis revealed solidification cracks in coatings deposited on carburized steel, regardless of processing parameters. However, preheating the substrate to 250 °C effectively eliminated cracking by reducing thermal gradients. The coatings exhibited a columnar dendritic microstructure, with coarser dendrites near the substrate and finer dendrites towards the surface. Hardness measurements confirmed that all coatings significantly exceeded the industry-specified threshold of 60 HRC, with preheating having minimal effect on overall hardness distribution. Reciprocating sliding wear tests demonstrated a substantial improvement in wear resistance for the defect-free HSLC coatings compared to baseline carburized steel. These findings underscore the potential of HSLC for producing high-performance, wear-resistant coatings suitable for industrial applications.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Interfacial analysis of the ex-situ reinforced phase of a laser spot welded Zr-based bulk metallic glass composite

To study the interfacial reaction of the ex-situ reinforced phase (Ta) of a Zr-based ((Zr{sub 48}Cu{sub 36}Al{sub 8}Ag{sub 8})Si{sub 0.75} + Ta{sub 5}) bulk metallic glass composite after laser spot welding, the interfacial regions of the reinforced phases located at specific zones in the welds including the parent material, weld fusion zone and heat affected zone were investigated. Specimen preparation from the specific zones for transmission electron microscopy analysis was performed using the focused ion beam technique. The test results showed that the reinforced phases in the parent material, weld fusion zone and heat affected zone were all covered by an interfacial layer. From microstructure analysis, and referring to the phase diagram, it was clear that the thin layers are an intermetallic compound ZrCu phase. However, due to their different formation processes, those layers show the different morphologies or thicknesses. - Highlights: • An ex-situ Zr-based BMG composite was laser spot welded. • The interfacial regions of the RPs located at PM, WFZ and HAZ were investigated. • The RPs in the PM, WFZ and HAZ were all covered by a ZrCu interfacial layer. • Due to different formation processes, those layers show the different morphology.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Improvement of the thermal stability of sintered Nd-Fe-B magnets by intergranular addition of Dy{sub 82.3}Co{sub 17.7}

In this study, microstructure and magnetic properties of sintered Nd-Fe-B magnets with addition of Dy{sub 82.3}Co{sub 17.7} (wt. %) were investigated. By adding a small amount of Dy{sub 82.3}Co{sub 17.7}, the coercivity is improved greatly, and the irreversible loss is decreased sharply. The increase of Curie temperature suggests that Co atoms have entered into the 2:14:1 main phase. Microstructural analysis indicates that a well-developed core-shell structure was formed in the magnets with the addition of Dy{sub 82.3}Co{sub 17.7}. The improvement of magnetic properties can be attributed to the microstructural modification and the intrinsic properties' improvement.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Deformation Behavior and Microstructure Evolution of Powder Metallurgy Ti6Al4V Alloy During Hot Compression

In order to determine appropriate workability parameters for cross-wedge rolling products of powder metallurgy (PM) Ti6Al4V alloys, thermal compression experiments were carried out within the temperature range of 850-1050 °C, the strain rate range of 0.1-10 s{sup −1}, and with a height decrease of 60%. The compression deformation behavior was investigated. A strain-compensated constitutive model was established based on the flow stress curves corrected by the friction, which can predict the flow behaviors under the entirety of the experimental deformation conditions. Moreover, the processing map was developed, and stable and unstable deformation regimes were established. The microstructure analysis illustrated that globularization and dynamic recrystallization were the main deformation mechanisms. The porosity of the compressed samples was greatly reduced and influenced by the temperature and strain rate. Considering the material flow stress, hot processing map, microstructure and porosity, the appropriate hot deformation parameters for PM Ti6Al4V alloy preforms are suggested.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Precipitation-site competition in duplex stainless steels: Cu clusters vs spinodal decomposition interfaces as nucleation sites during thermal aging

Competing microstructural evolution mechanisms can exist simultaneously when duplex stainless steels are operating for several decades in a high temperature service environment. Such competition between different microstructural evolution pathways can be difficult to ascertain using simple model alloy systems necessitating detailed structural and compositional analysis of phase transformation mechanisms in complex alloys Thus, in this study duplex stainless steels with complex but well understood chemistries were used to investigate the relative importance of different heterogeneous nucleation sites – specifically spinodal decomposition and Cu clustering – on precipitation of Ni-Si-Mn particles during long term thermal aging. Precipitation of Ni-Si-Mn particles in duplex stainless steels and ferritic steels during thermal aging and irradiation is known to have profound effect on mechanical properties. Using duplex stainless steels with custom modified compositions along with atom probe tomography characterization and first-passage kinetic Monte Carlo (FPKMC) simulations it is revealed that while the interface between Cr and Fe formed during spinodal decomposition can be a pathway for diffusion of Ni, Si, Mn, and Cu, it is not a site that encourages precipitation of Ni-Si-Mn rich particles. Instead, the presence of a higher concentration of Cu in these steels leads to formation of small Cu clusters with high energy interfaces that act as nucleation sites for Ni-Si-Mn particles because of its strong interaction particularly with Ni increasing the chemical driving force for precipitation. These results will help inform predictive models for the use of duplex stainless steels and other precipitation-hardened alloys for extended operation at high temperatures.

Duplex stainless steel, Thermal aging, Precipitati↗
DOE OSTI2018

Fabrication of Titanium-Niobium-Zirconium-Tantalium Alloy (TNZT) Bioimplant Components with Controllable Porosity by Spark Plasma Sintering

Spark Plasma Sintering (SPS) is used to fabricate Titanium-Niobium-Zirconium-Tantalum alloy (TNZT) powder—based bioimplant components with controllable porosity. The developed densification maps show the effects of final SPS temperature, pressure, holding time, and initial particle size on final sample relative density. Correlations between the final sample density and mechanical properties of the fabricated TNZT components are also investigated and microstructural analysis of the processed material is conducted. A densification model is proposed and used to calculate the TNZT alloy creep activation energy. The obtained experimental data can be utilized for the optimized fabrication of TNZT components with specific microstructural and mechanical properties suitable for biomedical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Structural transition in rare earth doped zirconium oxide: A positron annihilation study

Graphical abstract: New microstructural analysis and phase transition of rare earth doped mixed oxide compounds such as: Sm{sub 2−x}Dy{sub x}Zr{sub 2}O{sub 7} (where x = 0.0 ≤ x ≥ 2.0) that are potentially useful as solid oxide fuels, ionic conductors, optoelectronic materials and most importantly as radiation resistant host for high level rad-waste disposal, structural transition in the system is reported through positron annihilation spectroscopy as there is an indication in the X-ray diffraction analysis. Highlights: ► Zirconium oxide material doped with rare earth ions. ► The method of positron annihilation spectroscopy suggests a phase transition in the system. ► The crystal structure transformation from pure pyrochlore to defect fluorite type of structure is shown by X-ray diffraction results. -- Abstract: A series of compounds with the general composition Sm{sub 2−x}Dy{sub x}Zr{sub 2}O{sub 7} (where 0 ≤ x ≥ 2.0) were synthesized by chemical route and characterized by powder X-ray diffraction (XRD) analysis. The rare earth ion namely Sm{sup +3} in the compound was gradually replaced with another smaller and heavier ion, Dy{sup +3} of the 4f series, there by resulting in order–disorder structural transition, which has been studied by positron annihilation lifetime and Doppler broadening spectroscopy. This study reveals the subtle electronic micro environmental changes in the pyrochlore lattice (prevalent due to the oxygen vacancy in anti-site defect structure of the compound) toward its transformation to defect fluorite structure as found in Dy{sub 2}Zr{sub 2}O{sub 7}. A comparison of the changes perceived with PAS as compared to XRD analysis is critically assayed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of Mn on eutectic phase equilibria in Al-rich Al-Ce-Ni alloys

Microstructural analysis of additively manufactured (AM) Al-Ce-Ni-Mn alloys has identified phases not predicted from existing ternary liquidus projections in the Al-Ce-Ni system. Because the rapid cooling rate of AM is orders of magnitude above that of traditional casting, it is unclear if these additional phases arose from the non-equilibrium processing conditions of AM, a drastic shift in phase stability in the system due to the addition of 1 wt% Mn, or some combination of these two influences. The phases and microstructure of cast samples of Al-Ce-Ni and Al-Ce-Ni-Mn alloys were characterized for several annealing conditions which revealed the equilibrium phases at different temperatures. Phase analysis confirmed that minute levels of Mn substituted for Ni in the system drastically shifts the liquidus projection in the Al-rich corner of the ternary phase diagram such that the eutectic Al 3 Ni phase is suppressed in favor of the Al 23 Ni 6 (Ce,Mn) 4 phase. Further addition of Mn promotes the formation of Al 20 Mn 2 Ce and Al 10 Mn 2 Ce phases. The phase analysis data was then used to improve the CALPHAD modeling of the liquidus projection and isothermal sections for the Al-rich Al-Ce-Ni-Mn quaternary system. Thermodynamic modeling and experimental analysis on phases in the AM sample of Al-Ce-Ni with Mn confirmed that the phases present are consistent with Mn-containing Al-Ce-Ni cast samples. Here, this investigation demonstrates the potential for using secondary alloying elements to drastically alter phase stability and microstructure in alloy systems.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Effects of pyrolysis conditions on dielectric properties of PLZT films derived from a polyvinylpyrrolidone-modified sol-gel process

Graphical abstract: SEM images showing the surface morphology of PLZT films derived from solutions with various PVP content and treated with either RTA (rapid thermal annealing) or SPT (step-wise preheat treatment) process. Highlights: Black-Right-Pointing-Pointer High-quality PLZT films were fabricated by using a polyvinylpyrrolidone-modified sol-gel method. Black-Right-Pointing-Pointer Improved film density and integrity was achieved by employing a novel step-wise preheat treatment (SPT) process. Black-Right-Pointing-Pointer Enhanced dielectric properties were correlated to the improved microstructures as a result of the SPT process. -- Abstract: Pb{sub 0.92}La{sub 0.08}Zr{sub 0.52}Ti{sub 0.48}O{sub 3} (PLZT) films were deposited on platinized silicon substrates (Pt/Si) using a polyvinylpyrrolidone (PVP) modified sol-gel method. Pyrolysis of the green films was conducted via two methods: rapid thermal annealing (RTA) and a step-wise preheat treatment (SPT). Microstructure analysis and dielectric property characterization were performed on samples treated by these two methods. Results showed that the SPT-pyrolyzed films exhibited much better dielectric properties when compared with the RTA-pyrolyzed films. The differences in dielectric properties were correlated to microstructural features caused by the different pyrolysis conditions. High-quality PLZT films with high dielectric constant ( Almost-Equal-To 860 at zero bias) and high breakdown strength ( Almost-Equal-To 2.1 MV/cm) were fabricated under controlled pyrolysis conditions. This work demonstrated the potential application of this material for power electronics in electric drive vehicles.

36 MATERIALS SCIENCE↗