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The service of protective coatings at high temperature will lead to interdiffusion between the coating and superalloy. The occurrence of interdiffusion not only reduces the oxidation resistance of the coating but also reduces the mechanical properties of superalloys, especially single crystal superalloys. At present, the main methods of suppressing interdiffusion are: adding a diffusion barrier layer between the coating and superalloy, a so-called "equilibrium" (EQ) coating, and a nanocrystalline coating. In the current review, the advantages and disadvantages of these three methods for suppressing interdiffusion are discussed, and an attempt is made to determine the best method for suppressing interdiffusion to improve the service life of high-temperature components. [ABSTRACT FROM AUTHOR]

A two-layer Fe–Cr–Al–Zr surface alloy has been synthesized on a zirconium substrate by magnetron sputtering and subsequent low-energy high-current electron-beam (LEHCEB) processing. The thicknesses of the top Fe69Cr20Al11 (at.%) relatively large-grained (~1 μm) layer and the transition Fe–Zr–Cr–Al amorphous layer were about 0.7 and 0.6 μm, respectively. In turn, the amorphous layer consisted of two Fe64–54Zr8–22Cr21–17Al8–7 and Fe40–16Zr42–78Cr12–4Al6–2 (at.%) sublayers that differed in both zirconium and iron concentrations in wide ranges and were separated by another nanocrystalline interlayer. The Fe–Cr–Al–Zr surface alloy served as the diffusion barrier preventing the interaction of the zirconium substrate with oxygen from an environment. It was thermally stable up to ≈1173 K. [ABSTRACT FROM AUTHOR]

Iron aluminide coatings are very resistant to corrosion at 600-700 °C. However, interdiffusion is responsible for a significant reduction of the Al content at the coating surface. A stable diffusion barrier could in principle prevent this degradation mechanism. A new diffusion barrier based on nitrogen was produced and was very effective in reducing coating-substrate interdiffusion on P92. After nitriding P92, an Al slurry was applied and heat-treated, resulting in an overlay coating consisting of an Al solid solution with Cr and Fe. This coating was thinner and quite different from the several Al-Fe intermetallics obtained without nitriding and was fully characterized. A diffusion study was conducted and the results showed that after 2000 h at 650 °C, the new coating suffered very little changes and no interdiffusion with the substrate in contrast with the intermetallic coating deposited without nitriding. Testing under steam and fire-side atmospheres showed promising behavior. [ABSTRACT FROM AUTHOR]

A novel micro-tubular solid oxide fuel cell (SOFC) design with an inert support was proposed for operation on direct hydrocarbon fuels with an improved stability. In this design, the inert support also serves as a diffusion barrier between the fuel stream and Ni cermet anode. The barrier effect leads to higher local steam to carbon ratios in the anode, thus inhibiting carbon deposition. To demonstrate this concept, we fabricated micro-tubular SOFCs with a porous yttria-stabilized zirconia (YSZ) support. Ni, Ni-scandia-stabilized zirconia (ScSZ), ScSZ, strontium-doped lanthanum manganite (LSM)-ScSZ, and LSM were used as the anode current collector, anode, electrolyte, cathode, and cathode current collector, respectively. Good electrochemical performance was achieved with hydrogen and methane fuels in a temperature range 600-750 °C. Continuous cell operation on direct methane fuel for >40 h at 750 °C under moderate current densities delivered stable voltage without any evident performance degradation due to carbon deposition. The absence of carbon deposition on the anode and anode current collector layers was also confirmed by scanning electron microscope images and energy-dispersive X-ray spectra. We further discuss oxidation mechanism of the direct methane fuel and removal of the carbon possibly formed in the anodic layers during stability testing. [ABSTRACT FROM AUTHOR]

The results are provided for a study of the effect of high-temperature action duration in an air atmosphere at 1150°C for 100, 200, and 300 h on phase and chemical composition of heat-resistant layered coatings of the Al-Cr-Ni system. A collection of methods of electron microscopy (Z-contrast regime), energy-dispersion, and x-ray phase analyses shows that the main structural component of a diffusion barrier, providing a stable composition for a (NiAl + NiAl) coating and its heat resistance, are chromium-based solid solutions with a content in the range 93-99 at.%, and also solid solutions based on phases NiCr, NiCr, and NiAl. [ABSTRACT FROM AUTHOR]

A multilayer coating, which consisted of a Cr-Si co-deposited layer as the diffusion barrier, a plasma sprayed NiCrAlY middle layer, and an aluminized top layer, was developed. During the aluminizing treatment, Cr in the NiCrAlY layer was released as the γ/γ′ structure of this layer transformed to the β phase. The released Cr was inhibited by the inner Cr-Si layer to diffuse into the substrate, and a Cr layer eventually formed over the Cr-Si layer. The Cr layer impeded the inward diffusion of Al due to the low solubility of Al in the Cr layer so that more Al atoms remain in the coating and contributed to the oxidation resistance of the coating. The multilayer coating exhibited better oxidation and spallation resistance than coatings without a Cr-Si layer, at least at 1050 °C for up to 1000 h. [ABSTRACT FROM AUTHOR]

A novel approach to prepare a coating system containing an in situ grown CrO diffusion barrier between a nickel top layer and 310SS was reported. Cold spraying was employed to deposit Ni(O) interlayer and top nickel coating on the Cr-contained stainless steel substrate. Ni(O) feedstock was prepared by mechanical alloying of pure nickel powders in ambient atmosphere, acting as an oxygen provider. The post-spray annealing was adopted to grow in situ CrO layer between the substrate and nickel coating. The results revealed that the diffusible oxygen can be introduced into nickel powders by mechanical alloying. The oxygen content increases to 3.25 wt.% with the increase of the ball milling duration to 8 h, while Ni(O) powders maintain a single phase of Ni. By annealing the sample in Ar atmosphere at 900 °C, a continuous CrO layer of 1-2 μm thick at the interface between 310SS and cold-sprayed Ni coating is formed. The diffusion barrier effect evaluation by thermal exposure at 750 °C shows that the CrO oxide layer effectively suppresses the outward diffusion of Fe and Cr in the substrate effectively. [ABSTRACT FROM AUTHOR]

This study was performed in order to investigate a possibility to obtain Co-W microbumps via electrochemical routes, because this alloy recently has gained attraction as a novel barrier against copper diffusion. In order to be applied in flip-chip technology, barrier layers should be void-free and uniformly deposited on the entire area of a die to ensure high reliability and high performance of wafer bump-solder interface. To meet these requirements, a set of potentiostatic and galvanostatic electrodeposition was carried out from a citrate electrolyte, at pH 5 and at room temperature. The tests done confirm that void-free Co-W bumps with a uniform tungsten content along the bump can be obtained by potentiostatic and galvanostatic electrodeposition. Successful electrodeposition of Cu/Co-W/Sn layers with good adhesion between them and uniformity on the entire array of bumps also was obtained. The XPS data confirm that electrodeposited Co-W layers can act as a good barrier between Sn and Cu. [ABSTRACT FROM AUTHOR]

U-Mo alloys are being developed as low enrichment monolithic fuel under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Diffusional interactions between the U-Mo fuel alloy and Al-alloy cladding within the monolithic fuel plate construct necessitate incorporation of a barrier layer. Fundamentally, a diffusion barrier candidate must have good thermal conductivity, high melting point, minimal metallurgical interaction, and good irradiation performance. Refractory metals, Zr, Mo, and Nb are considered based on their physical properties, and the diffusion behavior must be carefully examined first with U-Mo fuel alloy. Solid-to-solid U-10 wt.%Mo versus Mo, Zr, or Nb diffusion couples were assembled and annealed at 600, 700, 800, 900 and 1000 °C for various times. The interdiffusion microstructures and chemical composition were examined via scanning electron microscopy and electron probe microanalysis, respectively. For all three systems, the growth rate of interdiffusion zone were calculated at 1000, 900 and 800 °C under the assumption of parabolic growth, and calculated for lower temperature of 700, 600 and 500 °C according to Arrhenius relationship. The growth rate was determined to be about 10 times slower for Zr, 10 times slower for Mo and 10 times slower for Nb, than the growth rates reported for the interaction between the U-Mo fuel alloy and pure Al or Al-Si cladding alloys. Zr, however was selected as the barrier metal due to a concern for thermo-mechanical behavior of UMo/Nb interface observed from diffusion couples, and for ductile-to-brittle transition of Mo near room temperature. [ABSTRACT FROM AUTHOR]

The suitability of P-doped g-C3N4 for sodium storage was assessed using density functional theory. The electronic structure of P-doped g-C3N4 was calculated and the results indicate that the presence of the P atom causes the band gap of g-C3N4 to narrow. Na adsorption on a P-g-C3N4 sheet was investigated. Projected density of states (PDOS) analysis revealed that pyridinic nitrogen atoms in g-C3N4 play the main role in Na adsorption. High binding energies were calculated for Na storage on g-C3N4, leading to a high voltage range (1–3 V) and a high Na diffusion barrier (2.3 eV). Doping the substrate with more P atoms resulted in lower voltages (below 2.2 V), easier Na diffusion (with a barrier of 1.2 eV), and therefore a material that was better suited than g-C3N4 for use in anodes. [ABSTRACT FROM AUTHOR]