Functional composite electrochemical coating Ni-Co-Al2O3 -an alternative to chromium plating

The physico-mechanical properties of composite electrochemical coatings (CEC) nickel-cobalt-aluminum oxide were investigated depending on the electrolyte parameters and electrolysis conditions. The previously developed low-concentration chloride electrolyte for nickel plating was used as an electrolyte to replace environmentally hazardous chromium plating electrolytes containing hexavalent chromium, which is prohibited by the laws of many countries. The wear resistance of the obtained CEC was determined on a three-ball friction machine. This made it possible to establish that the wear resistance of the CEC exceeds the wear of chrome coatings in dry friction mode by 2-2,5 times and is comparable to chromium in the friction mode with lubrication. In the dry friction mode, the higher wear resistance of the nickel-cobalt-alumina coating is explained only by the higher hardness of the latter. Probably, upon destruction of the coating, the particles of the alloying addition act as a solid lubricant, which causes an increase in the resistance of the CEC during wear. The microhardness of the CEC was determined using a PMT-3 microhardness tester and amounted to 6-25 GPa. The microhardness value was influenced by the concentration and properties of the dispersed phase, as well as the electrolysis conditions - the temperature and pH of the electrolyte, and the cathode current density. “Corrodcote” test was used in the study of corrosion. According to its data, the corrosion resistance of CEC is 2-3 times higher than the corrosion resistance of chromium deposits. The results obtained make it possible to recommend the developed functional CEC of nickel-cobalt-alumina instead of chromium coatings as corrosion- and wear-resistant.

Electrodeposition kinetics and surface morphology of Ni-B-UDD composite coating

The article presents the results of kinetic investigates of electrodeposition of a composite electrochemical coating based on a nickel-boron alloy. Current efficiency, polarization potentiodynamic researches had shown the joint participation in the electrodeposition process of finely dispersed compounds of nickel hydroxides, poorly soluble nickel and boron compounds present in the electrolyte or formed during electrolysis, and ultradispersed diamond introduced into the electrolyte. Comparison of 2D and 3D scans of the surfaces of the formed coatings confirmed the leveling effect of additives, as well as sparingly soluble nickel and boron compounds on the structure of coatings. The proposed composite electrochemical coatings can be used instead of chrome coatings when restoring parts and units of agricultural machinery.

Service properties of composite electrochemical coating

The article considers the ways of solving problems, regarding the rework and durability improvement of elements of industrial equipment. One of the ways to restore and improve the operational properties of machinery parts is the application of galvanic coatings, in particular, composite galvanic coatings. The article shows ways to improve the performance properties of composites, determines the optimal content of the dispersed phase in the composite, in terms of the ratio of the strength of the dispersed phase and matrix. The composite electrochemical coating wear resistance and the roughness of composites under conditions of abrasive wear have been explored. The relationship between the wear resistance and the surface roughness during wear has been determined. In an experimental study of the composite coatings abrasive wear resistance, it was found that their wear largely depends on the size and volume content of dispersed particles in the coating. It has been experimentally proven that the composite coating roughness depends on the matrix mechanical properties, the content and size of disperse particles.

Precipitation of Composite Wear-Resistant Nickel Ectrodeposits with Nanoparticles

The composition of the electrolyte-colloid was optimized by the method of mathematical planning of extreme experiments of Box-Wilson to obtain a composite electrochemical coating of nickel-nanodiamond. Polarization researches have shown a decrease in polarization in electrolytes containing diamond nanoparticles. The effect of the colloidal phase introduced into the electrolyte or formed during the electrolysis process on the electroplating process and the quality of precipitation was discussed. The wear resistance, microhardness, corrosion resistance of these deposits was investigated. These semi-bright and wear-and corrosion-resistant (Corrodcote-test) coatings are recommended as a substitute for electroplated chromium (better ecology). The morphology and surface of electroplating nanoparticles based on nickel were investigated using the «semi-contact» method on a PHYWE atomic force microscope. The leveling effect of diamond nanoparticles is shown.

Создание противокоррозионного композиционного цинкового покрытия стали для эксплуатации в средах, содержащих сульфатредуцирующие бактерии

В статье исследовано создание композиционного электрохимического покрытия (КЭП) цинк-ингибитор со включением в состав органического вещества (ОС), обладающего биоцидным и ингибирующим действиями, которое может быть применено для защиты стали от коррозии в средах, содержащих сульфатредуцирующие бактерии (СРБ). Покрытие наносилось на сталь методом электрохимического осаждения. Включение ОС осуществлялось путём модификации сернокислого электролита цинкования. Оценка защитного действия КЭП против микробиологической коррозии проведена в ходе лабораторного исследования образцов с покрытиями, находящимися в инокулированной СРБ питательно среде Постгейта Б в течение 7 суток. В ходе исследования определены такие параметры, как изменения электродного потенциала образцов в среде, водородного показателя и окислительно-восстановительного потенциала среды, концентраций бактериальных клеток и биогенного сероводорода. По окончании испытаний определены скорость коррозии и защитный эффект покрытия гравиметрическим методом. Оценка ингибирующего действия проведена методами электрохимической импедансной спектроскопии и поляризационных кривых образцов с КЭП, экспонируемых в течение 7 суток в инокулированной СРБ питательной среде Постгейта Б . В ходе исследования обнаружены: улучшение структуры покрытия благодаря введению ОС, биоцидное и ингибирующие действия КЭП, снижение скорости коррозии КЭП приблизительно в 2 раза по отношению к цинковому покрытию.The article investigated the creation of a composite electrochemical coating (CEC) zinc-inhibitor with the inclusion of an organic compound (OC) with biocidal and inhibitory effects, which can be used to protect steel from corrosion in environments containing sulfate-reducing bacteria (SRB). The coating was applied to steel by electrochemical deposition. The OC was turned on by modifying the zinc sulfate electrolyte. The evaluation of the protective effect of CEC against microbiological corrosion was carried out during a laboratory study of samples with coatings placed in a Postgate B inoculated SRB medium for 7 days. In the course of the study, such parameters as changes in the electrode potential of samples in the medium, hydrogen index and redox potential of the medium, concentrations of bacterial cells and biogenic hydrogen sulfide were determined. At the end of the tests, the corrosion rate and the protective effect of the coating by the gravimetric method were determined. Evaluation of the inhibitory effect was carried out by electrochemical impedance spectroscopy and polarization curves of samples with CEC, exposed for 7 days in inoculated SRB nutrient medium Postgate B. The study found: improvement of the coating structure due to the introduction of OC, the biocidal and inhibitory effects of CEC, a decrease in the corrosion rate of CEC by about 2 times with respect to the zinc coating.

Formation features of composite electrochemical nickel and nanostructured zirconium boride coatings

Introduction.The electrodeposition of composite electrochemical coatings from electrolyte-colloid nickel plating containing ultradisperse zirconium boride powder is studied. The work objectives are as follows: to study mechanical-and-physical properties of the composites based on nickel and nanostructured zirconium boride, and to determine optimal conditions for the application of such electrochemical coatings.Materials and Methods.Microhardness of composite electrochemical coatings was measured using PMT-3 microhardness tester on samples with the layer thickness of 30 μm under the indentation load of 100 g. A three-ball machine was used to determine wear resistance of the coatings. Sample tests were carried out under dry friction modes and with the use of 3% RV coolant. WSD values were measured by MIR-3 TU 3-3.1954-86 microscope. To determine the internal stresses in the coating, we used a flexible cathode method up to GOST 9.302-88.Research Results.The electrolyte-colloid composition and modes of electrodeposition of composite nickel - nanostructured zirconium boride coatings are developed. Mechanicaland-physical properties (microhardness, wear resistance and internal stresses) of the obtained composite electrochemical coatings are analyzed. Recommendations for use of the developed electrolyte and the application of a composite coating on machine parts for their surface hardening are formulated.Discussion and Conclusions. Ni–ZrB2 CEC (composite electrochemical coating) has high microhardness (10–11 hPa at the indentation load of 100 g), which exceeds the microhardness of pure nickel by 1.5–2 times. As the microhardness increases, the internal stresses ofNi–ZrB2 CEC decrease. The proposed coatings were compared to chromium ones deposited from the environmentally hazardous electrolytes. The wear resistance ofNi–ZrB2 CEC is 2–5 times higher than that of chromium coatings. Thus, instead of chromic coatings, it is recommended to use the proposed composition for surface hardening of parts of the specialty machinery and industrial equipment