The compound boronizing of H13 steel sample was carried out by adding rare earth CeO₂, and the effects of main parameters of compound boronizing on the properties of the boronizing layer were investigated. The boronizing kinetics were also analyzed. Under the conditions of boronizing temperatures of 850 °C, 900 °C, 950 °C, and 1000 °C, and boronizing times of 2 h, 3 h, 4 h, and 5 h, the boronizing experiment was carried out by adding CeO₂ with mass fraction of 2%, 4% and 6%, Cr₂O₃ with a mass fraction of 1%, 2%, 3%, and 4%. The results show that boronizing H13 steel with rare earth CeO₂ is conducive to the diffusion of boron atoms and can significantly improve the thickness and microhardness of boronizing layer. Boronizing kinetic analysis shows that the diffusion activation energy of boron atom decreases significantly when the rare earth content is 4%, which indicates that the content of rare earth CeO₂ with 4% is an ideal selection for considering improving the utilization rate of rare earth materials, and the boronizing kinetic analysis can provide a quantitative basis for determining the content of rare earth metals. Therefore, experiments and analysis show that for H13 steel, when the boronizing temperature is 950 °C, time is 4 h and rare earth content is 4%, the thickness of the boronizing layer can reach 71 μm and the microhardness at the depth of 70 μm from the surface layer can reach 1546.32 HV. Moreover, on this basis, when Cr₂O₃ with a rare earth content of 2% is added, the microstructure and wear resistance of the boronizing layer are significantly improved.

The spinning cup, a crucial component of textile equipment, relies heavily on 2A12 aluminum alloy as its primary raw material. Commonly, electroplating and chemical nickel–phosphorus (Ni-P) plating are employed to improve the surface characteristics of the object. Nevertheless, due to the growing expectations for the performance of aluminum alloys, the hardness and wear resistance of Ni-P coatings are no longer sufficient to fulfill industry standards. This study primarily focuses on the synthesis of Ni-B-PTFE nanocomposite chemical plating and its effectiveness when applied to the surface of 2A12 aluminum alloy. We examine the impact of the composition of the plating solution, process parameters, and various other factors on the pace at which the coating is deposited, the hardness of the surface, and other indicators of the coating. The research findings indicate that the composite co-deposited coating achieves its optimal surface morphology when the following conditions are met: a nickel chloride concentration of 30 g/L, an ethylenediamine concentration of 70 mL, a sodium borohydride concentration of 0.6 g/L, a sodium hydroxide concentration of 90 g/L, a lead nitrate concentration of 30 mL, a pH value of 12, a temperature of 90 °C, and a PTFE concentration of 10 mL/L. The coating exhibits consistency, density, a smooth surface, and an absence of noticeable pores or fissures. The composite co-deposited coating exhibits a surface hardness of 1109 HV_0.1, which significantly surpasses the substrate’s hardness of 232.38 HV_0.1. The Ni-B-PTFE composite coating exhibits an average friction coefficient of around 0.12. It has a scratch width of 855.18 μm and a wear mass of 0.05 mg. This coating demonstrates superior wear resistance when compared to Ni-B coatings. The Ni-B-PTFE composite coating specimen exhibits a self-corrosion potential of −6.195 V and a corrosion current density of 7.81 × 10⁻⁷ A/cm², which is the lowest recorded. This enhances its corrosion resistance compared to Ni-B coatings.

GCr15 bearing steel is widely used in the textile, aerospace, and other industries due to its excellent mechanical properties. However, traditional electroless Ni-B coatings can no longer meet the growing demand for a long service life under high-speed and heavy load conditions. This study focused on depositing Ni-B-Mo alloy coatings on GCr15 steel. An orthogonal experimental design was adopted to investigate the effects of the NiCl₂ and Na₂MoO₄ concentrations and deposition time on the deposition rate and surface hardness of the coatings. The results show that the Na₂MoO₄ concentration has the most significant impact on the deposition rate. An optimal concentration of 5.6 g/L improved both the deposition rate and hardness (up to 881 HV), while excessive Na₂MoO₄ (>15.6 g/L) reduced the coating adhesion and wear resistance. A deposition time of 1–2 h ensured a high deposition rate, but after 3 h, bath component depletion lowered the rate and caused coating defects. The NiCl₂ concentration (20–30 g/L) had a relatively minor influence on the deposition rate but stabilized the Ni²⁺ ion supply, enhancing the coating compactness. The optimized parameters were 5.6 g/L Na₂MoO₄, 25 g/L NiCl₂, and 2 h of deposition. The coating exhibited high hardness, strong adhesion, and excellent wear resistance. After heat treatment at 400 °C for 1 h, the coating transitioned from being amorphous to nanocrystalline, forming Ni₂B, Ni₃B, and Mo₂C phases, increasing the hardness from 737.49 HV to 916.19 HV and reducing the friction coefficient to 0.38.

Научная статья. Ползуновский вестник, 2020, 3

ВЛИЯНИЕ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ НА СТРУКТУРУ МАЛОУГЛЕРОДИСТОЙ СТАЛИ ПОСЛЕ ПОВЕРХНОСТНОГО УПРОЧНЕНИЯ И ТЕРМИЧЕСКОЙ ОБРАБОТКИ

Chemical-thermal treatment in general and borating in particular are highly effective ways to increase the service life of working bodies and machine parts, as well as tools. At the same time, it is necessary to select possible grades of steels, which are preferably subjected to boriding, depending on the goal. To solve practical problems in order to control the quality of a boride diffusion coating, there is a need to determine the strength and morphological characteristics of the boride layer and its phase composition. Since the high- boride FeB phase has low performance characteristics (high brittleness, creates tensile stresses on the surface, leading to cracking and spalling in the boride layer), in most cases the content of the FeB phase in the coating is limited to an upper limit of no more than 10–15 % of the thickness of the boride layer. Determination of the phase composition of boride layers is preferably carried out by electron microscopy methods, however, under production conditions, this is a laborious task. One of the options for analyzing the structure and morphology of the results obtained is the visualization of the phase composition of boride diffusion layers using "color etching'' with the possibility of assessing the structural-phase state using optical microscopy. It is shown that the electrolytic etching method proposed in this work in a saturated aqueous solution of alkaline sodium picrate makes it possible to obtain high-contrast images of the microstructure of the boride layer, which can subsequently be automatically processed in modern software systems for metallographic analysis in order to qualitative and quantitative assessment of the structural-phase state. Compared to the chemical methods of "color etching", the electrochemical etching method does not require highly skilled personnel and can be used in a production laboratory. Химико-термическая обработка в целом и борирование являются высокоэффективными способами повышения ресурса работы рабочих органов и деталей машин (инструмента). При этом необходимо подбирать марки сталей, которые предпочтительно подвергать борированию в зависимости от поставленной цели. Для решения практических задач в целях контроля качества боридного диффузионного покрытия имеется потребность определения прочностных и морфологических характеристик боридного слоя и его фазового состава. Высокобористая фаза FeB имеет низкие эксплуатационные характеристики (высокая хрупкость, создает на поверхности растягивающие напряжения, приводящие к трещинообразованию и сколам в боридном слое), в большинстве случаев содержание фазы FeB в покрытии ограничивают верхним пределом (не более 10 – 15 % от толщины слоя боридов). Определение фазового состава боридных слоев предпочтительно вести методами электронной микроскопии, однако в условиях производства это является трудоемкой задачей. Одним из вариантов анализа структуры и морфологии полученных результатов является визуализация фазового состава боридных диффузионных слоев с использованием «цветного» травления с возможностью оценки структурно-фазового состояния при помощи оптической микроскопии. Показано, что предложенный метод электролитического травления в насыщенном водном растворе щелочного пикрата натрия позволяет получить высококонтрастные изображения микроструктуры боридного слоя, которые в последующем могут быть автоматически обработаны в современных программных комплексах металлографического анализа с целью качественной и количественной оценки структурно-фазового состояния. По сравнению с химическими методами «цветного» травления, метод электрохимического травления не требует высокой квалификации персонала и может быть использован в условиях производственной лаборатории.