Simulation of Corrosion Resistance of Nanocomposites Fe (Co)-W

The problem of the formation of functional coatings, combining such important consumer properties as corrosion resistance, hardness, wear resistance and catalytic activity, is key in the creation of new materials for modern instruments, devices and technologies. The great practical interest in Co-W and Fe-W alloys is explained by the prospect of their use in industry as thermo, wear and abrasion-resistant, magnetic-hard materials, possessing high microhardness and being an alternative to hard chrome coatings [1-6]. In addition, such materials can be used as the basis of catalytic systems in >hydrogen energy, for the disposal of wastewater, toxic emissions of vehicles and industrial enterprises, reducing material costs and improving environmental safety [7,8].

Coatings were deposited on rectangular samples made of steel from citrate electrolytes at direct and pulse current density of 3.0-4.5 A/dm² [9-11]. The chemical composition of the coatings was determined using the energy-dispersion spectrometer Oxford INCA Energy 350 with the integrated programming environment SmartSEM. The surface morphology of alloys was investigated using the scanning electron microscope ZEISS EVO 40XVP, and the topography was studied using the microscope NT-206 with the probe CSC-37. The structure of the deposits was examined by X-ray diffraction analysis using a diffractometer DRON-3.0 in monochromatic Co-Kα radiation. The corrosion properties of the binary deposits were determined by polarization resistance and impedance technique. The spectra of electrochemical impedance were measured on the Autolab-30 electrochemical module PGSTAT301N Metrohm Autolab in the frequency range 10^-2-10⁶Hz. Vickers microhardness Hv of coatings with alloys not less than 30 microns thick was determined by after 24 hours of aging of the coatings at room temperature under a load of 0.05kg and a holding time of 10s.

The common trends in the corrosion behavior of electrolytic Co (Fe)-W electrolytic alloys in an aggressive media is a decrease in the corrosion rate and opposite change in the open circuit potentials with an increase in the refractory metal content. The corrosion resistance of tungsten alloys significantly exceeds the resistance not only of steel substrates, but also of individual metals. To predict the corrosion resistance of the above alloys, thermodynamic functions of metals and their oxides, the energy and parameters of the crystal lattice, the binding energies of metals with oxygen and hydrogen and their differences, the specific electrical resistance of metals and oxides, etc., were used as input parameters for Artificial Neural Networks (ANN) analysis [12]. The output variable is the corrosion rate of the alloys in various environments. From the analysis of a large number of ANNs of various architecture, it was found that the minimal error in predicting the Co-W corrosion rate in aggressive solutions is achieved by a generalized regression ANN with two hidden layers. And a multilayer perceptron with two hidden layers exhibits the smallest error in predicting the corrosion rate for Fe-W coatings. The microhardness of coatings Co(Fe)-W of ω (W)=40-50 mas% rises up to 500-600 in comparison with alloying metals (Co-130, Fe-150, W-400) [13-15].

Corrosion-electrochemical behavior of coatings of iron (cobalt)-tungsten alloys in environments of different acidity depends on the content of the refractory component, and the increase in corrosion resistance in an acidic environment is due to the formation of acidic tungsten oxide on the surface. Simulation of the corrosion processes using ANN artificial neural networks show the most important parameters determining the corrosion resistance of alloys to be electrical conductivity of metals and their oxides; metal-oxygen binding energy; standard enthalpies of formation and entropy of oxides WO₃, Co₃O₄, Fe₃O₄. The microhardness of electrolytic alloys of tungsten with iron (cobalt) depends on its content and exceeds the characteristics of coatings with individual metals, which allows to recommend such materials as an alternative to hard chromium coatings.

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