In-depth characterization of as-deposited and annealed Fe-W coatings electrodeposited from glycolate-citrate plating bath

Fe-W coatings with 4, 16 and 24 at.% of W were electrodeposited under galvanostatic conditions from a new environmental friendly Fe(III)-based glycolate-citrate bath. This work aims to find correlations between composition including the light elements, internal structure of the electrodeposited Fe-W alloys and functional properties of material. The obtained alloys were characterized by Glow Discharge Optical Emission Spectrometry (GD-OES), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD). Compositional depth profiles of 10 μm thick coatings obtained by GD-OES show that the distribution of metals is uniform along the entire film thickness, while SEM imaging depicted the presence of cracks and O- and W-rich areas inside the Fe-W coating with 4 at.% W. In the samples with 16 and 24 at.% of W, oxygen and hydrogen are present mostly at the surface about 1 μm from the top while traces of carbon are distributed within the entire coatings. With increasing W content, the structure of the coatings changes from nanocrystalline to amorphous which was shown by XRD and TEM analysis. Also, the surface of coatings becomes smoother and brighter, that was explained based on the local adsorption of intermediates containing iron and tungsten species. Annealing experiments coupled with XRD analysis show that the thermal stability of Fe-W alloys increases when the W content increases, i.e. the coating with 24 at.% W retains the amorphous structure up to 600 °C, where a partially recrystallized structure was observed. Upon recrystallization of the amorphous samples the following crystalline phases are formed: α-Fe, Fe2W, Fe3W3C, Fe6W6C, and FeWO4. Hence, the Fe-W coatings with higher W content (>25 at.%) can be considered as suitable material for high temperature applications

Enhanced mechanical properties and microstructural modifications in electrodeposited Fe-W alloys through controlled heat treatments

Among W alloys, Fe-W has seen much attention recently, due to the need of moving toward the design of environmentally friendly materials. Coatings with 4, 16 and 24 at.% of W were electrodeposited from an environmental friendly Fe(III)-based glycolate-citrate bath. The samples were annealed in vacuum at different temperatures up to 800 °C. Different crystalline phases are formed upon annealing: α-Fe, Fe2W, Fe3W3C, Fe6W6C, and FeWO4. Their grain size and distribution within the coating was studied by means of Electron Backscattered Diffraction (EBSD) technique. The effect of annealing on the mechanical properties of the coatings was analyzed performing nanoindentation measurements. The results show a considerable increase of the hardness followed by a rapid decrease at higher temperatures. The highest hardness value, i.e. 16.5 GPa, is measured for the sample with 24 at.% of W after annealing at 600 °C owing to the precipitation of α-Fe crystallites. This study indicates the possibility to substantially increase the hardness of electrodeposited Fe-W coatings by optimization of the annealing treatment. In addition, the critical influence of the carbide and oxide phases on the mechanical properties of alloys is discussed. Hence, Fe-W coatings rich in W can be applied as a possible candidate for protective coating applications at elevated temperatures

Toward uniform electrodeposition of magnetic Co-W mesowires arrays : direct versus pulse current deposition

Template-assisted electrodeposition of Co-rich Co-W alloys into mesoporous anodized aluminum oxide from ammonia-free solutions is investigated. The optimum deposition conditions rendering uniform filling of the pores, either by direct current (DC) or pulse current (PC) methods, are established. Contrary to the DC deposition on flat surfaces (which is kinetically controlled), the DC electrodeposition in the mesopores of the template is limited by mass transfer. Conversely, under PC mode, the Co-W electrodeposition process is controlled by kinetics at frequencies > 0.3 Hz; and by diffusion at lower frequencies. The obtained mesowires are nanocrystalline and exhibit a hexagonal closed packed (hcp) structure. The magnetic properties of selected Co-W mesowires, with variable aspect ratio, are also studied. The arrays of mesowires exhibit a semi-hard ferromagnetic behavior with coercivity values that surpass those of Co mesowires with similar dimensions. The interplay between interwire dipolar interactions, magnetocrystalline anisotropy and shape anisotropy on the overall shape of the hysteresis loops (in particular, on the coercivity and squareness ratio values, as well as on the effective magnetic easy axis direction) is investigated in a semiquantitative manner

Tribological behaviour of Co-W under dry and lubricanting conditions

The dry and lubricating wear was investigated for steel and Co-W samples in the view of revealing the best performance of tungsten alloys. The tribological behaviour was studied under bi-directional ball-on-flat sliding tests: 10 N and 50 000 cycles. The given research identified that Co-W coatings have superior wear resistance than those of uncoated samples (steel ST3) under dry and also under lubricating conditions. Thus, wear volume of Co-W samples is decreasing two times under dry conditions and ten times under lubricating conditions. The use of new type of solid lubricant (sugar film) is discussed

Aluminum Alloys Anodisation for Nanotemplates Application

The aim of this investigation was to reveal the processing differences in achieving nanoporous anodized aluminium from aluminium alloys and their application for cobalt nanowires electrodeposition. The following types of aluminium were tested: pure Al (99.99%), commercial AA1050 alloy, commercial 6082 alloy and commercial 6060 alloy. Because of the differences in the surface temperature and high voltages during the anodizing steps, some stresses can be built up in the material. Therefore a strict temperature control should be was done to limit thermal stresses in materials. Alloying elements (Si, Mg) cause precipitates that are observed on the surface, especially for 6060 alloy. Nevertheless, a nanoporous structure can be obtained at the end of second anodization step on all aluminium alloys investigated. It was shown that the number density of pores on the surface is practically independent on the aluminium alloys used. However, the degree of hexagonal distribution of the pores depends on the type of anodized aluminium alloy. Also, a successful fabrication of Co nanowire arrays using nanoporous anodic alumina template produced on Al alloy has been demonstrated, and the uniform filling of the template by cobalt nanowires arrays is discussed

Evaluation of corrosion and tribological behavior of electrodeposited tungsten alloys

Tungsten alloy coatings with iron group metals (Ni, Fe, Co) are considered as advanced materials for various surface engineering applications. Such coatings should be resistant to mechanical and corrosive damage, and to have improved functionality and durability. Accordingly, the objectives of this review consist in a comparative study of available literature on corrosive and wear behavior of electrodeposited tungsten alloys with iron group metals, including our recent results on evaluation of electrodeposited Co-W coatings. The wear and corrosion resistance of Ni-W, Fe-W and Co-W strongly depends on the chosen deposition conditions and subsequently on tungsten content and structure of obtained protective coatings

Sliding and wear-resistance of electrodeposited cobalt-tungsten coatings: dependence on synthesis parameters

In this work the tribological properties of Co-tungsten coatings electrodeposited by direct and pulse mode were investigated. These coatings are widely used in microtechnics and micromachining. At low current density the coatings contain a low concentration of tungsten that leads to the formation of milky coatings with high roughness, low hardness, high coefficient of friction, and high wear. At a higher current density (1 A/dm²) the coating properties approach these of hard coatings like hard chromium and TiN.status: publishe

Tribocorrosion properties of nanocrystalline W-rich Co–W, Ni–W and Fe–W coatings

Electrodeposited binary tungsten-rich alloys with iron-group metals, namely Co, Ni and Fe, reveal great potential that makes them suitable as surface coatings for engineering materials. In this context, tribocorrosion plays an important role in the lifetime of such engineering materials e.g. metallic machinery components. In the present paper, the corrosion behaviour of electrodeposited ultra-nanocrystalline Co–32W, Ni–29W and Fe–31W (in at.%) was investigated by monitoring the open circuit potential (OCP) before and after the sliding against an alumina ball in 0.5 M Na3PO4 solution. The W-rich alloy coatings were compared in terms of friction coefficient during sliding; and wear track evaluation. Under the experimental conditions of the present study, the results showed that all investigated alloys are in active state and the corrosion resistance under sliding occurs through the dissolution of W and iron group metals along with the formation of oxides – wear debris on the contact surface