The electroplating of iron-chromium and iron-nickel-chromium layers is an economic alternative to mild steel and hard-chrome layers from chromium (VI) electrolytes. Iron-chromium and iron-nickel-chromium layers were electrodeposited using an environment friendly chromium (III) electrolyte. The layers were heat-treated at different temperatures (150 °C, 300 °C, 450 °C and 600 °C) in order to determine the temperature at which recrystallization takes place, which phases are formed and to study the influence on the element content. The phase analysis was conducted by X-ray diffraction, the chemical composition and the microstructure were characterized by the scanning electron microscopy. Both layer systems show an X-ray-amorphous structure that begins to recrystallize at a temperature of 450 °C. From a heat-treatment temperature of 600 °C, the organic additives decompose and the oxygen forms chromium oxide with the chromium.
The electrodeposition of iron-nickel-chromium coatings is a more environmentally friendly and economical alternative to hard-chrome coatings made from chromium (VI) electrolytes and stainless-steel bulk materials. The aim of the study was to develop a suitable deposition method for thick and low-crack Fe-Cr-Ni coatings. Iron-nickel-chromium coatings were electrodeposited using a more ecological chromium (III) electrolyte with direct current (DC), stepped direct current, and pulse current (PC). The influence of the deposition method on the electrolyte aging, the alloy composition of the coating, and their microstructure was investigated. Corrosion studies of the Fe-Cr-Ni coatings in 3.5% NaCl solution were performed using polarization tests. Furthermore, hardness measurements and scratch tests were carried out to determine the adhesion strength. Phase analyses were performed by X-ray diffraction, and the chemical composition and microstructure were characterized by scanning electron microscopy. Using the stepped DC and PC method, crack-free Fe-Cr-Ni coatings were successfully deposited.
The simulation of large-scale industrial electrodeposition of zinc is of major importance, since through the simulation, important data about the positioning of electrodes, thickness of layers, etc. can be generated. But the models used in practical applications indirectly assume small anodes and cathodes for which the electrical potential or the charge-transfer current are constant over the cathode, resp. anode. In this paper, a new type of model for the dissolution of zinc anodes is described. Furthermore, a numerical scheme to treat the model will be described and verified. The new model will be compared to a commonly known model. The paper gives an alternative model for the calculation of the current density on anodes and formulates a FEM for the approximation of Poisson equations on multiple domains with Robin-interfaces. Besides the application to the dissolution of zinc-anodes during electro-plating, the basic model and FEM can be applied to the dissolution of anodes made of a different material and to the modelling of corrosion processes.
This study shows the electrodeposition of Fe-Cr-Ni alloys using the advantages of a stepped direct-current deposition in a Cr(III)-containing electrolyte, and its influence on the pH value. The resulting coatings are uniform and free of microcracks, with a Cr content around 30% and thicknesses above 10 µm. The influence of the current mode (direct current, stepped direct current, pulsed current) on pH development is investigated and correlated with the arising microstructure and alloy composition. Considering the current flow, it can be stated that pauses interrupt high overvoltage and restrain the pH increase at the cathode. The associated formation of chromium hydrides and their deposition onto the chromium layer, leading to cracking, is thus reduced. In this work, direct evidence for this theory and a suggestion for near-surface pH measurement during electrodeposition are presented.
Potentiodynamic and potentiostatic polarization tests in the potential range between open circuit potential (OCP) − 0.1 V and OCP + 4 V were carried out in aluminate–phosphate electrolytes with an aluminate concentration of 0.2 mol/L and varying phosphates contents between 0 and 0.1 mol/L. The pH was adjusted between 11.5 and 12.0 due to phosphate and optional KOH addition. A high-strength, dual-phase steel, which is relevant for lightweight construction, served as the substrate material. The layer microstructure was investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy and Raman spectroscopy were used for element and phase analyses. We found that iron hydroxides or oxides are initially formed independently of the electrolyte composition at low potentials. At around 1 V vs. standard hydrogen electrode (SHE), the current density suddenly increases as a result of oxygen evolution, which causes a significant reduction in the pH value. Precipitation leads to the formation of porous layers with thicknesses of 10 µm to 20 µm. In the case of a pure aluminate solution, the layer mainly consists of amorphous alumina. When adding phosphate to the electrolyte, the layer additionally contains the hydrous phosphate evansite. At the highest phosphate content in the electrolyte, the highest P content and the most pronounced crack network were observed.
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