Multilayer nickel-tungsten coatings were deposited on carbon steel using the pulse reverse current technique. Nickel-tungsten layered structure coatings were developed using the continuous and ...alternative variation of pulse duty cycle at two specific and fixed values. In these coatings, the multilayer structure is composed of two nickel-tungsten layers with alternating chemical compositions of 25 wt%W and 11 wt%W. Dynamic electrochemical impedance spectroscopy (DEIS) revealed three time constants in the electrical equivalent circuit corresponding to the electrodeposition mechanism of nickel-tungsten. In order to evaluate the electrochemical behavior of the multilayer structure, the investigation of the multilayer coatings was carried out via cyclic potentiodynamic polarization, in a sulfuric acid media which contained chloride ions. Cyclic voltammetry test was introduced and subsequently employed as a novel electrochemical evaluation for layered structures. Morphological, elemental and Raman analysis were carried out. Analyzing the surface products revealed that nickel tends to dissolve in presence of tungsten, and even more in an electrolyte containing chloride ions. It was also revealed that the diffusive species of the electrolyte encountered a larger interface in multilayer structures. Hence, they spread out along and throughout the active layers; which significantly delays the penetration towards the substrate. Enhanced service life of the noble layers is achieved owing to the galvanic effect. According to the findings, these kinds of coatings are more resistant to localized attack in comparison to monolithic coatings.
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A common cause for premature bearing failures in wind turbine gearboxes are the so-called White Etching Cracks (WEC). These undirected, three-dimensional cracks are bordered by regions of altered ...microstructure and ultimately lead to a cracking or spalling of the raceway. An accelerated WEC test was carried out on a FE8 test rig using cylindrical roller thrust bearings made of martensitic 100Cr6 steel. The resulting WECs were investigated with several characterisation techniques. Ultrasonic measurements showed the WEC were mainly located in the region of the overrolled surface in which negative slip occurs, which agrees with hypotheses based on an energetic approach for a prognosis. SEM orientation contrast imaging of the area around WEC revealed an inhomogeneous structure with varied grain sizes and a large amount of defects. Microstructure characterization around the WEA using EBSD showed significant grain refinement. Atom probe tomography showed the microstructure in the undamaged zone has a plate-like martensitic structure with carbides, while no carbides were detected in the WEA where the microstructure consisted of equiaxed 10nm grains. A three dimensional characterisation of WEC network was successfully demonstrated with X-ray computerized tomography, showing crack interaction with unidentified inclusion-like particles.
•Accelerated laboratory WEC test successfully carried out.•Electron backscatter diffraction of WEC region.•3D characterization of nanocrystalline WEA using atom probe tomography.•3D characterisation of WEC network using X-ray tomography.
Nickel–tungsten with satisfactory corrosion properties is a promising alloy to replace hard chromium. Relatively high adhesion between copper substrate and electrodeposited Ni–W alloy results in ...patterned morphology due to crack formation. In this work, corrosion resistance of patterned Ni–W alloys comprising 0–26
at.%.W were studied by potentiodynamic polarization and EIS in a medium containing Cl
−. It is shown that corrosion resistance of single phase Ni–W is superior to amorphous and dual phase coated layers. It is also found that crack density is the dominant affecting factor on corrosion resistance of amorphous Ni–W alloys.
Although several typical manifestation of novel coronavirus disease 2019 (COVID-19) including respiratory symptoms, weakness, fever, and fatigue have been reported, some rare and novel manifestations ...have also been observed, particularly in children. We report a pediatric case of fulminant hepatic failure associated with COVID-19. Although the patient was treated for acute fulminant hepatic failure in the context of COVID-19, he died following the progression of the disease to stage 4 hepatic failure with encephalopathy and brain death.
In this study plasma nitriding is applied on nickel–aluminum composite coating, deposited on steel substrate. Ni–Al composite layers were fabricated by electro-deposition process in Watt’s bath ...containing Al particles. Electrodeposited specimens were subjected to plasma atmosphere comprising of N
2–20% H
2, at 500
°C, for 5
h. The surface morphology investigated, using a scanning electron microscope (SEM) and the surface roughness was measured by use of contact method. Chemical composition was analyzed by X-ray fluorescence spectroscopy and formation of AlN phase was confirmed by X-ray diffraction. The corrosion resistance of composite coatings was measured by potentiodynamic polarization in 3.5% NaCl solution. The obtained results show that plasma nitriding process leads to an increase in microhardness and corrosion resistance, simultaneously.
Summary
On the example of electrodeposited nickel films, it is shown that unique information on twins with dimensions on the nanoscale can be obtained by suitable combination of ion channelling ...imaging and electron backscatter diffraction analysis, whereas both (routine) single techniques cannot meet the requirements for analysis of these films. High‐resolution electron backscatter diffraction is inadequate for full characterization of nanotwins, but image quality maps obtained from electron backscatter diffraction at least yield a qualitative estimation of the location and number of nanotwins. Complementing this information with ion channelling imaging provides more representative insights into the microstructure, because it supplements the quantitative investigation of the number and width of twin lamellae with additional crystallographic orientation analysis provided by EBSD. To this end, two methods for adjusting EBSD data based on ion channelling images are proposed. Thorough selection of the complementary techniques opens future perspectives for the investigation of other challenging samples with nanoscale features in the microstructure.
Nanocrystalline nickel-tungsten alloys are of high industrial interest owing to their mechanical properties, wear and corrosion resistance, as well as their thermal stability. Since the patterning of ...their structures potentially enhances mechanical and tribological characteristics, layered nickel-tungsten alloys were developed by sequential electrodeposition of bi-layers (two different concentrations of tungsten) in the current study. The layer thickness was modulated in the range of 90 to 3000 nm. Using a modified pulse reverse current technique, all the layers were deposited from a fixed citrate-based electrolyte. Studying the material by microhardness and Palmqvist techniques revealed that the microhardness of the coatings was improved by reduction of layer thicknesses, in accordance with Hall-Petch relation. Wear test results indicated that layered coatings were more resistant in comparison with the monolithic counterparts. Furthermore, microscopy investigations showed that by reducing the layer's thickness, the plastically deformed region underneath the wear front narrows, thus increasing the load-bearing capabilities.
•Nanocrystalline NiW coatings deposited with multilayered structure•Mechanical and wear properties were studied as a function of layer thickness.•A comprehensive study of wear mechanism of multilayer coatings was performed.•The concept of load bearing capability was representatively discussed.
A sulfate-based electrolyte was used for synthesis of multilayer (ML) and monolithic Ni-Fe-Al2O3 coatings. The ML electrodeposits were achieved by consecutive alteration of duty cycle of pulsed ...current between two values of 20% and 90%. The influences of the ML microstructure on mechanical properties and wear resistance of composite coatings were studied. The shear punch testing method was employed to evaluate the room temperature mechanical properties. It was shown that increasing the pulse frequency and decreasing the pulse duty cycle improved the mechanical properties of monolithic coatings. The electrodeposited ML coatings exhibited a pronounced improvement in microhardness, shear strength and wear resistance in comparison to the monolithic coatings. Pin-on-disk sliding wear tests revealed that the main mechanisms of wear are plastic deformation, fatigue crack of deformed layers and delamination.
The cementation of cadmium ions by zinc powder was studied in a batch reactor at low and high concentrations at pH 5.2–5.4 and it is shown that the reaction is first-order. XRD and SEM analysis ...confirm that the deposited layer is metallic with no evidence of basic zinc sulphate or re-dissolution of cadmium. Dependence of the reaction constant on initial cadmium concentration proves the reaction mechanism. Different possible kinetic controlling models of cadmium ion (Cd
2+) cementation from aqueous solution by zinc powder were studied with respect to initial cadmium concentration, temperature, zinc powder size and stoichiometric ratio. The experiments demonstrate that at initial cadmium concentrations >
1000 ppm, the ash diffusion control model prevails, while at concentrations <
500 ppm, the data has good agreement with the film diffusion model. For concentrations between 500 ppm and 1000 ppm, a combination of ash diffusion and film diffusion models controls the reaction rate. Based on numerical analysis, the calculated activation energies at high and low concentrations are 9.6 and 7.2 kJ/mol, respectively. Statistical data analysis was performed and different reaction rate constants were estimated from the equations for high and low initial cadmium concentrations.
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