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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Severe Hot Corrosion of the Superalloy IN718 in Mixed Salts of Na{sub 2}SO{sub 4} and V{sub 2}O{sub 5} at 700 °C

This study presents hot corrosion behavior of the superalloy IN718 in 100 wt.% NaCl (salt S) and in salt mixtures of 60 wt.% Na{sub 2}SO{sub 4} + 40 wt.% V{sub 2}O{sub 5} (SM1) and 75 wt.% Na{sub 2}SO{sub 4} + 15 wt.% NaCl + 10 wt.% V{sub 2}O{sub 5} (SM2), deposited separately by spray gun technique, at elevated temperature of 700 °C. The weight gain per unit area at 700 °C was increased by 49% for salt S, 153% for the dual salt mixture SM1, and only 8% for the triple salt mixture SM2, in comparison with that observed earlier at 600 °C. The marked increase in the severity of corrosion at 700 °C is attributed to formation of the highly damaging compound NaVO{sub 3} that significantly enhances the oxygen activity, in the SM1 coated samples. The effect of surface roughness and dislocation density on corrosion behavior at 700 °C, however, is found to be similar to that at 600 °C. Ultrasonic shot peening, a novel technique of surface modification, is found to enhance the hot corrosion resistance in the salt mixture SM1 at 700 °C appreciably due to extensive grain refinement to nanoscale and formation of highly protective Cr{sub 2}O{sub 3} layer in the surface region.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tribo-corrosion and Albumin Attachment of Nitrogen Ion-Implanted CoCrMo Alloy During Friction Onset

In this paper, CoCrMo alloy surface was implanted with 100 keV nitrogen ions to modify it. Bovine serum albumin (BSA) adsorption and the initial behavior of tribo-corrosion in the simulated system were studied. Nitrogen ion implantation can promote BSA dynamic adsorption due to the change of friction and wear mechanisms. From the tribo-corrosion test results, the open circuit potential (OCP) increased to about 0.6 V and the coefficient of friction (COF) decreased to about 0.2 for the nitrogen ion-implanted CoCrMo compared with the untreated sample before the modified layer failure. The point when the open circuit potential and the coefficient of friction changed during long wear time (1, 2 and 4 h) is considered the sign of the worn through modified layer. Then, the OCP of the implanted sample rose by 0.3 V compared with the untreated sample, and the COF remained at around 0.3, which is lower compared with the COF of untreated sample after the modified layer has been worn through. Thus, nitrogen ion implantation not only improved wear and corrosion resistance of the CoCrMo alloy, but also promoted BSA adsorption on the CoCrMo alloy surface, which effectively reduced the wear volume and metal ions release.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Size-dependent stochastic tensile properties in additively manufactured 316L stainless steel

Recent work in metal additive manufacturing (AM) suggests that mechanical properties may vary with feature size; however, these studies do not provide a statistically robust description of this phenomenon, nor do they provide a clear causal mechanism. Because of the huge design freedom afforded by 3D printing, AM parts typically contain a range of feature sizes, with particular interest in smaller features, so the size effect must be well understood in order to make informed design decisions. This work investigates the effect of feature size on the stochastic mechanical performance of laser powder bed fusion tensile specimens. A high-throughput tensile testing method was used to characterize the effect of specimen size on strength, elastic modulus and elongation in a statistically meaningful way. The effective yield strength, ultimate tensile strength and modulus decreased strongly with decreasing specimen size: all three properties were reduced by nearly a factor of two as feature dimensions were scaled down from 6.25 mm to 0.4 mm. Hardness and microstructural observations indicate that this size dependence was not due to an intrinsic change in material properties, but instead the effects of surface roughness on the geometry of the specimens. Finite element analysis using explicit representations of surface topography shows the critical role surface features play in creating stress concentrations that trigger deformation and subsequent fracture. The experimental and finite element results provide the tools needed to make corrections in the design process to more accurately predict the performance of AM components.

316L stainless steel↗
DOE OSTI2020

Structural integrity of additively manufactured stainless steel with cold sprayed barrier coating under combined cyclic loading

Integration of metal additive manufacturing (AM) and cold spray (CS) technologies provide an unprecedented opportunity to manufacture coated material systems with complex geometrical features. The application of these material systems in functionally critical components requires adequate structural integrity, particularly in the presence of cyclic loading. This article researches the multiaxial fatigue (axial-torsional cyclic loading) behavior of a coated material system consisting of 15Cr-5Ni precipitation-hardening stainless steel (15-5 PH SS) substrate additively manufactured by direct metal laser sintering with a layer of chromium carbide nickel (CrC-Ni) barrier coating deposited by CS. The influence of AM and CS-induced residual stresses on fatigue performance of test specimens was thoroughly studied. Additionally, the effect of surface roughness and processes induced defects were considered to explain the crack growth mechanism. Stresses assessed by synchrotron X-ray diffraction indicated a substantial accumulation of residual stresses, particularly in the outer surface of the as-fabricated 155 PH SS specimens. The state of residual stress was changed notably following the deposition of CrC-Ni coating in the axial, hoop, and radial directions of the fatigue test specimen. Also, CS deposition of CrC-Ni coating caused significant improvement in the surface quality of the additively manufactured components. Fatigue test results indicated, CS deposition of CrC-Ni substantially enhances the fatigue life of the AM-produced 15-5 PH SS substrate in all loading conditions, particularly in the high cycle fatigue regime. The improvement in the fatigue life of the specimens with coating was associated with a reduction in equivalent residual stress at the substrate surface and improvement in the specimens' surface condition (i.e., reduced surface roughness). The fractographic analysis of the specimen indicated the cracks tend to initiate in the surface of both as-fabricated and cold-sprayed specimens. However, the mechanism of crack growth changed notably following the deposition of CrC-Ni coating. The cracks tended to propagate in the planes parallel or with a small deviation from the build layers of the AM-produced specimens. On the other hand, deposition of CrC-Ni coating increased the deviation of crack growth plane from the build layers of the substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Quantifying and reducing the differences in forest CO 2 -fluxes estimated by eddy covariance, biometric and chamber methods: A global synthesis

Carbon dioxide (CO 2 ) fluxes between terrestrial ecosystems and the atmosphere are primarily measured with eddy covariance (EC), biometric, and chamber methods. However, it is unclear why the estimates of CO 2 -fluxes, when measured using these different methods, converge at some sites but diverge at others. We synthesized a novel global dataset of forest CO 2 -fluxes to evaluate the consistency between EC and biometric or chamber methods for quantifying CO 2 budget in forests. The EC approach, comparing with the other two methods, tended to produce 25% higher estimate of net ecosystem production (NEP, 0.52Mg C ha-1 yr-1), mainly resulting from lower EC-estimated Re; 10% lower ecosystem respiration (Re, 1.39Mg C ha-1 yr-1); and 3% lower gross primary production (0.48 Mg C ha-1 yr-1) The discrepancies between EC and the other methods were higher at sites with complex topography and dense canopies versus those with flat topography and open canopies. Forest age also influenced the discrepancy through the change of leaf area index. The open-path EC system induced >50% of the discrepancy in NEP, presumably due to its surface heating effect. These results provided strong evidence that EC produces biased estimates of NEP and Re in forest ecosystems. A global extrapolation suggested that the discrepancies in CO 2 fluxes between methods were consistent with a global underestimation of Re, and overestimation of NEP, by the EC method. Accounting for these discrepancies would substantially improve the our estimates of the terrestrial carbon budget .

Wang, Xingchang↗
DOE OSTI2021

Daily grass reference evapotranspiration with Meteosat Second Generation shortwave radiation and reference ET products

Here we assess the accuracy of estimating daily grass reference evapotranspiration (PM-ET o ) using daily shortwave radiation (R s ) and reference evapotranspiration (ET REF ) products provided by the Meteosat Second Generation (MSG) geostationary satellite delivered by the Satellite Applications Facility on Land Surface Analysis (LSA-SAF) framework. The accuracy of using reanalysis ERA5 shortwave radiation data (R s ERA5 ) provided by the European Center for Medium-Range Weather Forecasts (ECMWF) is also evaluated. The assessments were performed using observed weather variables at 37 weather stations distributed across continental Portugal, where climate conditions range from semi-arid to humid, and 12 weather stations located in Azores islands, characterized by humid, windy and often cloudy conditions. This study&#x27;s use of data from a variety of climate conditions contributed to a unique and innovative assessment of the usability of LSA-SAF and ERA5 products for ET o estimation. The first assessment focused on comparing LSA-SAF estimates of R s (R s LSA-SAF ) against ground stations (R s ground ). The results showed a good matching between the two R s data sets for continental Portugal but a tendency for R s LSA-SAF to under-estimate R s ground in the cloudy islands of Azores. ET o values computed using R s LSA-SAF data and observed temperature, humidity and wind speed (ET o LSA-SAF ) were then compared with PM-ET o estimates with ground-based data, which were used as benchmark; input data of temperature and humidity needed for PM-ET o were quality checked for surface aridity effects. It was observed that ET o LSA-SAF is strongly correlated with PM-ET o (R 2 > 0.97) for most locations in continental Portugal, with regression coefficient of a linear regression forced to the origin ranging between 0.95 and 1.05, mean root mean square error (RMSE) of 0.13 mm d –1 , and Nash and Sutcliff efficiency of modeling (EF) above 0.95. For most Azores locations, ET o LSA-SAF over-estimated PM-ET o . This is likely a consequence of the high spatio-temporal heterogeneity of weather conditions that occur in these oceanic islands together with the different footprints of satellite (averaged over the pixel) and station observations. Reanalysis ERA5 shortwave radiation data presented similar behavior to the LSA-SAF products, however with slightly lower accuracy. The daily LSA-SAF ET REF product (ET REF LSA-SAF ) was assessed and results have shown a good accuracy of this product, with acceptable RMSE and high EF values, for continental Portugal but a low accuracy for the Azores islands. A simplified bias correction approach was shown to improve both ET o derived from the LSA-SAF products, namely for Azores stations, which seem to be representative of smaller areas. The use of the FAO-PM temperature approach (PMT) was also assessed using the R s LSA-SAF and R s ERA5 data, which showed a superiority of the LSA-SAF product for ET o estimations (ET o PMT LSA-SAF ). No significant differences (p < 0.05) were observed in terms of the median value of the RMSE when adopting ET o PMT and ET REF LSA-SAF . Differently, results showed that using the R s LSA-SAF in the PMT approach (ET o PMT LSA-SAF ) produces significantly better RMSE results than ET o PMT and ET REF LSA-SAF . Overall, the performed assessment allows concluding that the use of R s LSA-SAF, and to a lesser extent the use of the R s ERA5 , highly improves the accuracy of computation of ET o when R s observations are not available, including when only temperature data are accessible. The use of the ET REF LSA-SAF product is a good alternative when observed weather data are not available.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Effects of temperature on surface-controlled dislocation multiplication in body-centered-cubic metal nanowires

Recent computational studies revealed that screw dislocations in body-centered-cubic (bcc) metal nanowires can self-multiply through cross-slip near the free surface. This unique process was termed surface-controlled dislocation multiplication (SCDM). In bcc metals, screw dislocation motion and its cross-slip behavior are often related to thermally activated processes; due to this relation, SCDM is expected to be highly temperature-sensitive. In this study, therefore, we investigated how temperature influences the SCDM in bcc molybdenum and niobium nanowires using atomistic simulations. Regardless of the difference in lattice resistance at a given temperature, both systems show similar trends of critical shear stress of SCDM with respect to temperature. Further, the temperature dependence was found to be divided into three different regimes; (1) lattice-resistance-dominant; (2) segmentation-dominant; (3) steady-state segmentation. The presence of these three regimes will be discussed in terms of the temperature-dependence of the lattice resistance and the dynamics of dislocation segmentation in the nano-scale volume. Our results provide a fundamental understanding of screw dislocation behavior in bcc metals at the nanometer scale and varying temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Ab initio molecular dynamics study of SiO2 lithiation

Li-ion batteries (LIBs) are sought to meet the demand for high energy storage applications. Due to its high specific charge capacity and low discharge potential, SiO 2 is a promising candidate material for LIBs anodes. To design high performance anodes and coating materials using SiO 2 , understanding the structural transformation and Li-ion kinetics in different structural forms of SiO 2 is essential. Here, we performed ab initio molecular dynamics to study the lithiation mechanism for crystalline and amorphous SiO 2 and the effect of surface termination to elucidate the lithiation process of conversion oxides and contribute to the development of future LIBs.

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

Decontamination of urban surfaces contaminated with radioactive materials and consequent onsite recycling of the waste water

Enhancing rapid remediation strategies is paramount for recovery after a large-scale nuclear contamination event in an urban environment. Some current strategies recommend use of readily available equipment, materials, and facilities to expedite recovery. For example, applying pressurized water to contaminated surfaces may effectively remove radioactive contamination. In this study, a commercial power washer removes soluble forms of 152 Eu 3 + , 85 Sr 2 + , and 137 Cs + contamination from common porous building materials, and computer simulations characterize the recycling of the resultant contaminated wash water. Pressure washing the porous building materials under spray conditions typical with do-it-yourself units improved decontamination factors (DFs) for 152 Eu compared to low-pressure application of tap water (majority of two-tailed t-test p-values < 0.1), but pressure did not improve DFs for 137 Cs or 85 Sr. For both pressurized and low-pressure applications, adding potassium ions (K + ) to promote ion exchange reactions produced significantly higher DFs for tested radionuclides on asphalt, brick, and concrete. The resultant contaminated wash water can be processed through self-prepared chemical filtration beds of clay and sand. Modeled in a prior study, the beds yielded linear trends (R 2 > 0.98) in sensitivity analyses between most bed configuration variables and bed performance variables, permitting flexible ad-hoc bed design. The experimental and simulation results led to estimates of the remediation rate and waste generated after cleaning 250 m 2 of cesium-contaminated concrete from the combined deployment of a power washer and two different mobile treatment beds. Furthermore, the first treatment bed was designed to reduce treatment time and processed 1900 L of wash solution in 70 min using 880 kg of clay/sand infill material. Designed to reduce the solid waste generated, the second bed processed the same solution volume in 1040 min (17 h) using 170 kg of clay/sand infill material. The results of this analysis warrant further investigation of power washing with recycled salt solution as an effective rapid decontamination method with manageable waste.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Computer simulation of reaction and transport of core-scale serpentinization of Fe-bearing olivine and evolution of geological hydrogen

We present reactive flow and transport simulations of core-scale serpentinization of forsteritic, Fe-bearing olivine under hydrothermal conditions. The model captures fluid flow, evolving porosity–permeability, and redox-controlled H 2 production in a cylindrical core over 55 days at 245 °C and 37 bar. Key processes include olivine dissolution, precipitation of serpentine and magnetite, and oxidation of Fe2+ to Fe 3+ . Here, results show strong coupling among flow velocity, alteration front propagation, and spatially heterogeneous H 2 generation. Elevated H2 concentrations align with inlet-localized magnetite precipitation, consistent with experiments. Secondary mineral formation reduces porosity and permeability, altering transport pathways. Reactive flow at the fluid–solid interface governs H 2 generation rates and distribution. Dissolved SiO2 promotes serpentine and talc formation by suppressing brucite, while bicarbonate extends reaction duration and moderates surface complexation effects.

Geologic hydrogen↗
DOE OSTI2019

In-situ TEM study of microstructural evolution in NFA and Cr 3 C 2 @SiC-NFA composite during ion irradiation

In this article, the ion irradiation responses of a Fe-based nanostructured ferritic alloy or ‘NFA’ (Fe–9Cr–2W–0.2V–0.4Ti–0.3Y 2 O 3 ) and a Cr 3 C 2 @SiC-NFA composite were assessed. In-situ ion irradiation with TEM observation was carried out by using 1 MeV Kr ++ ions at doses of 0, 1, 3, 5, 10 dpa and temperatures of 300 °C and 450 °C. Both the NFA and Cr 3 C 2 @SiC-NFA samples showed significant dislocation density after 10 dpa at 300 °C. However, the Cr 3 C 2 @SiC-NFA composite showed a significantly lower dislocation loop density and a smaller average loop size during the irradiation at 450 °C as opposed to the NFA. At 300 °C, 1/2<111> type dislocation loops were observed in both the NFA and Cr 3 C 2 @SiC-NFA samples. Interestingly, at 450 °C, <100> type loops were dominant in the NFA sample while 1/2<111> type loops were still dominant in the Cr 3 C 2 @SiC-NFA sample. The results were discussed based on the large surface sink effects and enhanced interstitial-vacancy recombination at higher temperatures. Lastly, the additional Si element in the Cr 3 C 2 @SiC-NFA sample might have played a significant role in determining the dominant loop types.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Decoupling the effects of substrate hardness and roughness upon particle adhesion in cold spray

There are two stages of particle adhesion relevant to cold spray: adhesion of the first layer to the substrate, followed by inter-particle adhesion during subsequent deposition. In this work we study the second of these, in which particles strike a previously-deposited layer that is roughened and hardened by prior particle impacts. Specifically, we decouple the effects of surface roughness and hardness on particle adhesion for copper-on-copper impacts. We measure changes to the critical velocity, V cr , in single particle impacts produced by the Laser Induced Particle Impact Test on several surfaces including a cold sprayed surface and a polished version of that surface. We find that increases in both substrate roughness and hardness suppress particle adhesion to higher velocities, indeed in rather equal proportion by ∼10–15% each. This suggests that there is a higher V cr associated with coating build-up (particle-particle bonding) that is overall ∼30% higher than V cr for particle-substrate adhesion.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Portable Distortion Free Large Solid Angle Coverage Detector

Neutron single crystal diffractometers require large solid angle coverage for optimum performance. This can be achieved by tiling flat detectors in a cylindrical or spherical geometry, but results in large gaps in detector coverage and parallax distortion. The detector edges exhibit degraded resolution, distortion, and gamma rejection. Since the detector edge regions are a significant fraction of the detector active area, they must be removed from the experimental data set, requiring extra beam time to collect enough analysis data. A spherical detector with a continuous surface would effectively address this issue while eliminating most boundary ‘dead’ areas. Here we report on the development of a novel hemispherical shaped neutron detector using seamlessly tiled readout modules to form the desired shape. The heart of the detector is a specially developed curved neutron scintillator coupled to high resolution silicon photomultiplier (SiPM) Anger cameras via custom made fiber optic tapers (FOTs). The detector has been assembled and initial tests have been conducted at the High Flux Isotope Reactor (HFIR) beamlines at Oak Ridge National Laboratory (ORNL). Here, in this work, we describe details of the scintillator design, fabrication and characterization, evaluation of individual detector modules, the details of the detector design implementation, and evaluation of the assembled detector at ORNL beamlines.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗