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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Crystal plasticity modeling for the strengthening effect of multilayered copper–graphene nanocomposites

The paper explores plastic deformation mechanisms in metal–graphene nanocomposites, illustrating their material strengthening effects through a crystal plasticity finite element (CPFE) model. This model is compared with published experimental results, which have previously shown that the two-dimensional shape of graphene effectively controls dislocation motion and significantly enhances the strength of metals. Simulated nanopillar compression tests, using a physics-based CP model that incorporates surface nucleation and single-arm source dislocation mechanisms, help us understand dislocation motions at submicron length scales. The crystal plasticity models are applied to nanolayered composites with copper grain layers and monolayer graphene, featuring repeat layer spacings of 200 nm, 125 nm, and 70 nm, respectively. This study quantifies the accumulation of dislocations at the graphene interfaces, contributing to the ultra-high strength of copper–graphene composites. Furthermore, a Hall–Petch-like correlation is established between yield strength and the number of embedded graphene layers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Production and characterization of TRISO fuel particles with multilayered SiC

Three distinct composite architectures of silicon carbide (SiC) and pyrocarbon (PyC) were incorporated into the SiC coating layer of tristructural-isotropic (TRISO) nuclear fuel particles. The composite architectures are meant to increase the resistance of SiC coating layer to cracking and fission product attack during operation and accident scenarios. All composite layers were produced using the existing fluidized bed chemical vapor deposition apparatus that is used for production of TRISO fuel particles without modifications. Detailed characterization of the composite microstructure was carried out via optical and electron microscopy. Nano-indentation examination confirms that mechanical properties of the SiC phase was not affected in the composite architectures, however, the resistance to crack propagation in this coating layer was greatly increased in all cases when compared to the reference monolithic coating layer. The stress required to debond the SiC-inner PyC interface in the reference TRISO particles was determined to be ~1 GPa using micropillar compression technique. The high strength may explain the ease of crack propagation from the inner PyC to SiC in the reference design. In the composite architectures, the means of crack deflection were effectively incorporated at this interface. Lastly, finite element analysis of stress evolution in the fuel particles during normal operation with the reference and composite SiC coating layer architectures did not show any significant differences between the variants.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Microstructure evolution during annealing of TiAl/NiCoCrAl multilayer composite prepared by EB-PVD

TiAl/NiCoCrAl laminate composite sheet with a thickness of 0.4–0.6 mm as well as a dimension of 150 mm × 100 mm was fabricated successfully by using electron beam physical vapor deposition (EB-PVD) method. The annealing treatment was processed at 1123 and 1323 K for 3 h in a high vacuum atmosphere, respectively. The phase composition and microstructure of TiAl/NiCoCrAl microlaminated sheet have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on the sheet characterization and results of the microstructure evolution during annealing treatment process, the diffusion mechanism of interfacial reaction in TiAl/NiCoCrAl microlaminate was investigated and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Corrosion resistance of ZrO{sub 2}–TiO{sub 2} nanocomposite multilayer thin films coated on carbon steel in hydrochloric acid solution

This work reports the achievement of preparing of x% zirconia (ZrO{sub 2})–titania (TiO{sub 2}) composite coatings with different ZrO{sub 2} percent on the carbon steel by dipping substrates in sol–gel solutions. The prepared coated samples were investigated by various surface techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDAX). Open-circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods were employed to investigate the corrosion resistance of the coated carbon steel substrates in 1.0 M HCl solution at 50 °C. The data showed that, the corrosion protection property is not always proportional to the percent of ZrO{sub 2}. It can be inferred that there is an optimum percent (10%ZrO{sub 2}) for beneficial effects of loading ZrO{sub 2} on the protection efficiency (98.70%), while higher loading percent of ZrO{sub 2} in the sol–gel coating leads to the formation of a fragile film with poor barrier properties. EDAX/SEM suggests that the metal surface was protected through coating with ZrO{sub 2}–TiO{sub 2} composite films. - Highlights: • Sol–gel TiO{sub 2} doped with ZrO{sub 2} films deposited on carbon steel substrate • XRD measurements of x wt.% ZrO{sub 2}–TiO{sub 2} showed the (101) peaks broader than that of TiO{sub 2}. • SEM results proved that, the cracking decreases with the number of layers. • The prepared films can improve the corrosion resistance of the carbon steel substrate. • 10%ZrO{sub 2} loading is the optimal percent for useful effects on the corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Blue fluorescent organic light emitting diodes with multilayered graphene anode

As an innovative anode for organic light emitting devices (OLEDs), we have investigated graphene films. Graphene has importance due to its huge potential in flexible OLED applications. In this work, graphene films have been catalytically grown and transferred to the glass substrate for OLED fabrications. We have successfully fabricated 2 mm × 2 mm device area blue fluorescent OLEDs with graphene anodes which showed 2.1% of external quantum efficiency at 1000 cd/m{sup 2}. This is the highest value reported among fluorescent OLEDs using graphene anodes. Oxygen plasma treatment on graphene has been found to improve hole injections in low voltage regime, which has been interpreted as oxygen plasma induced work function modification. However, plasma treatment also increases the sheet resistance of graphene, limiting the maximum luminance. In summary, our works demonstrate the practical possibility of graphene as an anode material for OLEDs and suggest a processing route which can be applied to various graphene related devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced efficiency of large-area dye-sensitized solar cells by light-scattering effect using multilayer TiO2 photoanodes

Highlights: • DSSCs with an active area of 100.6 cm{sup 2} and light-scattering layers are fabricated. • The light-scattering effect is shown to enhance the light absorption in the red part of the solar spectrum. • The light-scattering effect is more important than the dye adsorption capacity for TiO{sub 2} photoanodes with same thickness. • The highest power conversion efficiency of 7.52% has been obtained by the DSSC with optimized conditions. - Abstract: In order to reduce the usage of photoactive dye and improve light harvesting by the photoanode of dye-sensitized solar cells (DSSCs), TiO{sub 2} scatting layers were introduced. We have investigated the light-scattering effect in large-area DSSCs with an active area of 100.6 cm{sup 2} that contain diffusing or reflective layers. The result shows that the light-scattering effect is more important than the dye adsorption capacity for the light harvesting property of TiO{sub 2} photoanodes with same thickness, and the light-scattering effect is shown to enhance the light absorption in the red part of the solar spectrum. The highest power conversion efficiency of 7.52% has been obtained by the cell with optimized high dye adsorption layer and high light-scattering layer, which is 9.5% higher than that of the cell without the light-scattering layer (6.87%).

14 SOLAR ENERGY↗
DOE OSTI2022

Facile fabrication of 2D material multilayers and vdW heterostructures with multimodal microscopy and AFM characterization

Reliable transfer processes that enable manipulation of two-dimensional (2D) materials, e.g., transition metal dichalcogenides (TMDCs) and MXenes, from one substrate to another has been a necessity for successful device fabrication. Here, with both mechanical exfoliation and chemical vapor deposition (CVD) widely used, a versatile, clean, deterministic, and yet simple transfer technique is highly needed. To address such need, we developed a transfer method that takes advantage of wettability contrast between interfaces without the use of sacrificial layers or chemical processes. More importantly, a setup was developed to carry out this transfer method with high sample selectivity and fine control of the position and orientation of transferred TMDC crystals, a feature required for fabrication of the devices based on vertical 2D heterostructures. Using both exfoliated and CVD grown materials and subsequent atomic force microscopy (AFM), photoluminescence (PL), confocal Raman and tip enhanced Raman spectroscopy (TERS) characterization, we ascertained the quality of interfaces resulting from the transfer process while preserving excellent 2D material integrity. PL and TERS maps revealed nanometer-scale heterogeneities in the interfaces of fabricated heterostructures, which should enable further perfection of the transfer technique. TERS/TEPL information were employed to identify areas suitable for nanodevice fabrication, making the reported transfer and characterization methods ideal for making high quality assembly of 2D heterostructure more accessible, which should facilitate exploration of vertical 2D heterostructures for applications in electronics, batteries, solar cells, and twistronics.

2D material transfer↗