Mathematical models that describe the dependences of the critical temperatures of pitting formation of AISI 304, 08Kh18N10, AISI 321, 12Kh18N10T steels in model circulating waters with pH 4…8 and chloride concentrations from 350 to 600 mg/l on their chemical composition and structure have been developed. They are based on linear squares regressions and a feed-forward neural network for reduced feature numbers. Using the developed mathematical models, it was found that the critical pitting temperatures of these steels increase with an increase in the pH of the circulating water, the number of oxides up to 3.95 μm in size, the average distance between titanium nitrides, the Cr content and a decrease in the concentration of chlorides in the circulating waters, the average distance between oxides and average austenite grain diameter. At the same time, it was found that the geometric dimensions of the steel structure most intensively affect their pitting resistance in circulating waters, and the effect of their chemical composition is minimal and is determined by the amount of Cr, which contributes to an increase in the pitting resistance of steels, probably increasing the solubility of nitrogen in the austenite solid solution. It is proposed to use the developed mathematical models to select the optimal heats of these steels for the production of heat exchangers and predict their pitting resistance during their operation in circulating waters.

Principles of three component Iron-Cobalt-Tungsten alloys electrodeposition from complex Fe (III) based citrate electrolytes are discussed. It is shown, that deposition of ternary alloys proceeds through competitive reduction of cobalt and tungsten with iron. With increasing ligand concentration coatings are enriched with a refractory component; however, increasing current density favors a reverse trend. The effect of both current density and pulse on/off time on the quality, content of alloying metals and surface topography of electrolytic coatings were determined. The application of pulsed electrolysis provides increasing tungsten content up to 13 at.%, at current efficiency of 70-75%. Globular relief of Fe-Co-W coatings is caused by refractory metals incorporation, and crystalline and amorphous parts of structure are visualized by X-ray spectroscopy, including inter-metallic phases Co 7 W 6 , Fe 7 W 6 along with α-Fe and Fe 3 C. The crystallite size of the amorphous part is near 7-8 nm. Corrosion resistance of the coatings is 1.3-2.0 orders of magnitude higher than the substrate parameters as follows from data of polarization resistance method and electrode impedance spectroscopy.

Abstract. The structure and the properties of the oxide films formed on titanium in the diphosphate based electrolytes by means of plasma electrolytic oxidizing at direct current density of 2-2.5 A· dm −2 have been studied. Oxide layers of different composition and content of alloying elements were obtained by modification of electrolytes and variation in current density. The interelectrode voltage during PEO, chemical and phase composition, topography and microstructure of the formed layers depend on the electrolyte composition and applied current density. The spark-discharge regime was shown to be reached at inter-electrode voltage 100 to 130 V depending on the composition of electrolyte. The effect of chemical composition and surface morphology formed mixed oxide films on the corrosion resistance and catalytic activity has been discussed. IntroductionTitanium is the most common oxide in heterogeneous catalysis and photo-catalysis for the purification gas and liquid media from toxicant [1,2]. This fact is attributed to the fairly high chemical stability under different operating conditions, no toxicity, and relatively low cost of this material. At the same time it was found that, in most cases, catalyst materials based on mixed two or three component oxide systems exhibit high activity and selectivity not only in heterogeneous red-ox reactions [3-5] but also in photo-catalytic ones [6][7][8]. Synthesis of nano-composite catalytic disperse systems based on titania is carried out by various methods, including sol-gel processes [6,9,10].The formation different kind of oxide layers has been achieved by the anodic oxidation and plasma surface treatment in the sparking regime (plasma electrolytic oxidizing PEO) seems to be the very promising since it does not need the sophisticated facilities, allows to form various types of titania and to incorporate different species into the layer by modification of electrochemical parameters and of electrolyte chemistry [11][12][13][14].Titania layers containing manganese oxides obtained by PEO in acetate-borate electrolyte was noted to be catalytic active in CO conversion to CO 2 [15]. Cobalt-containing oxide coatings on titanium are obtained from a silicate electrolyte with cobalt acetate addition [16]. However, the increase in the catalytic activity of above materials in CO oxidation reaction was achieved by additional impregnation followed by annealing. In [17] catalytic materials on titanium and aluminum doped with transition metal oxides (Mn, Fe, Co, Ni) were obtained in one stage by the PEO method,

Electrochemical method providing the possibility to check the penetrating porosity, corrosion resistance and phase composition of nitrided surface has been developed and applied for high-speed SW18 steel nitrided from plasma excited H 2 +N 2 gas mixture and for structural 10A and 45A steels nitrided from NH 3 gas dissociated at different parameters. By selection the appropriate electrolytes, the phase composition of nitrided layer in SW18 steel, and the corrosion resistance of  or γ' compact nitride layer on 10A and 45A steels have been evaluated and confirmed by material science and corrosion tests. Electrochemical methods may be applied to control the quality of obtained nitrided layer, and to correct or modify the program of technological process. Electrochemical method provided the possibility to check the penetrating porosity, corrosion resistance and phase composition of nitrided surface By selection the appropriate electrolytes, the phase composition and the corrosion resistance of nitride layers formed on SW18, 10A and 45A steels were established in accordance with the material investigation and corrosion tests data.

No abstract