Tribological Behavior of Reinforced PTFE Composites and Un-Reinforced Polyketone-Based Materials against Coated Steel

In this study, two polymeric materials were tested in a dry rotating “pin-on-disc” configuration against differently coated surfaces, to evaluate their tribological response under conditions, such as those of rotary lip seals, and to identify the wear mechanism of each coupling. A PTFE based material, reinforced with glass fibers and a solid lubricant, and unreinforced polyketone were tested against a chromium oxide coating deposited by plasma thermal spraying, a CrN/NbN superlattice coating deposited by Physical Vapor Deposition (PVD), and a Diamond-Like Carbon (DLC) coating obtained through a hybrid PVD/PECVD (Plasma-Enhanced Chemical Vapor Deposition) process. The PTFE matrix composite offers better overall performance, in terms of specific wear rates and friction coefficients than polyketone. Although the tribological behavior of this material is generally worse than that of the PTFE matrix composite, it can be used without reinforcing fillers. Our analysis demonstrates the importance of transfer-film formation on the counter-surfaces, which can prevent further wear of the polymer if it adheres well to the counterpart. However, the tribofilm has opposing effects on the friction coefficient for the two materials: its formation leads to lower friction for PTFE and higher friction for polyketone.

Study on the Effect of Deposited Graphene Oxide on the Fatigue Life of Austenitic Steel 1.4541 in Different Temperature Ranges

This paper presents the effect of deposited graphene oxide coating on fatigue life of austenitic steel 1.4541 at 20 °C, 100 °C, and 200 °C. The study showed a decrease in the fatigue life of samples with a deposited graphene oxide layer in comparison with reference samples at 20 °C and 100 °C. However, an increase in fatigue life of samples with a deposited graphene oxide layer in comparison with reference samples occurred at 200 °C. This relationship was observed for the nominal stress amplitude of 370 and 420 MPa. Measurements of temperature during the tensile failure of the sample and microfractographic analysis of fatigue fractures were performed. Tests have shown that graphene oxide deposited on the steel surface provides an insulating layer. A higher temperature of the samples with a deposited graphene oxide layer was observed during fracture compared to the reference samples.

Comparative Study of Structures and Properties of Detonation Coatings with α-Al2O3 and γ-Al2O3 Main Phases

This study is aimed at obtaining a coating of aluminum oxide containing α-Al2O3 as the main phase by detonation spraying, as well as a comparative study of the structural, tribological and mechanical properties of coatings with the main phases of α-Al2O3 and γ-Al2O3. It was experimentally revealed for the first time that the use of propane as a combustible gas and the optimization of the technological regime of detonation spraying leads to the formation of an aluminum oxide coating containing α-Al2O3 as the main phase. Tribological tests have shown that the coating with the main phase of α-Al2O3 has a low value of wear volume and coefficient of friction in comparison with the coating with the main phase of γ-Al2O3. It was also determined that the microhardness of the coating with the main phase of α-Al2O3 is 25% higher than that of the coatings with the main phase of γ-Al2O3. Erosion resistance tests have shown (evaluated by weight loss) that the coating with α-Al2O3 phase is erosion-resistant compared to the coating with γ-Al2O3 (seen by erosion craters). However, the coating with the main phase of γ-Al2O3 has a high value of adhesion strength, which is 2 times higher than that of the coating with the main phase of α-Al2O3. As the destruction of coatings by the primary phase, α-Al2O3 began at low loads than the coating with the main phase γ-Al2O3. The results obtained provide the prerequisites for the creation of wear-resistant, hard and durable layered coatings, in which the lower layer has the main phase of γ-Al2O3, and the upper layer has the main phase of α-Al2O3.

Study of the current waveform effect on the formation of cathode deposits during direct electrolysis. Part 2. Electrolysis of sea water

Поваренная соль является сырьем для получения гипохлорита натрия, при этом затраты на ее приобретение и доставку составляют до 25–30% от общей стоимости произведенного дезинфектанта. Альтернативным сырьем для получения гипохлорита натрия могут быть хлориды, содержащиеся в природной минеральной воде, например подземной, морской и океанической. Минеральная вода будет сырьем для получения раствора гипохлорита натрия достаточно высокой концентрации, который можно затем добавлять в обрабатываемую воду. Опыт эксплуатации установок «ХЛОРЭФС» производства ООО НПП «ЭКОФЕС» показал, что основная проблема надежности работы электролизеров связана с образованием отложений солей жесткости: карбоната кальция на поверхности катодного электрода и гидроксида магния на поверхности катодов электролизера. Это приводит к негативному режиму электролиза, росту напряжения, перегреву и короблению электродной системы, разрушению оксидного покрытия анодов и т. д. Приведены результаты исследований прямого электролиза постоянным и реверсным током соленой воды Южно-Вьетнамского моря. В испытаниях оценивали влияние реверсного тока в сравнении с постоянным током на снижение образования нерастворимых веществ на катодах электролизера, а также определяли технологические параметры электролиза. Выход хлора по току для морской воды был выше 100% в реверсном режиме с плотностью тока 100 А/м2. Sodium chloride is a raw material for the production of sodium hypochlorite; however, the cost of its purchase and delivery is up to 25–30% of the total cost of the disinfectant produced. An alternative raw material for the production of sodium hypochlorite can be chlorides present in natural mineral water, e. g., underground, sea and oceanic water. Mineral water will be the raw material for obtaining sodium hypochlorite solution of a sufficiently high concentration that can then be added to the treated water. The experience of operating CHLOREFS units manufactured by EKOFES SPE LLC showed that the main problem related to the electrolyzer operation reliability is associated with the formation of deposits of hardness salts – calcium carbonate on the surface of the cathodic electrode, and magnesium hydroxide on the surface of the electrolyzer cathodes. This results in a negative electrolysis regime, an increase in voltage, overheating and warping of the electrode system, destruction of the oxide coating of the anodes, etc. The results of studies of direct electrolysis by direct and reverse current of salt water of the South Vietnam Sea are presented. During the tests the effect of reverse current in comparison with direct current on the reduction of the formation of insoluble substances on the cathodes of the electrolyzer was estimated, and besides, the electrolysis process parameters were determined. The current chlorine yield for seawater was above 100% in the reverse mode with a current density of 100 A/m2.

Influence of the thickness and porosity of the oxide coating on the piston heads depending on the parameters of the microarc oxidation mode

This paper discusses the process of formation of an oxide coating (hardening and heat-insulating coating) on the working surfaces of the head (top and piston grooves) of the piston by the method of microarc oxidation (MAO). In the process of oxidation of the piston head, the operating parameters of MAO will have a significant effect on the thickness and porosity of a formed oxide coating. The paper presents the theoretical relationships between the electrical parameters of the microarc oxidation mode and the thickness and porosity of the oxide coating. The thickness of the formed oxide coating on the piston heads will depend on the applied voltage and the composition of the electrolyte used. The porosity of the formed oxide coating will depend on the parameters of the current strength and the applied voltage. It is theoretically established that the formation of an oxide coating of a certain thickness and porosity occurs due to changes in the current strength, voltage and time of microarc oxidation.

Influence of the parameters of the process conditions for microarc oxidation on the formation of the thickness and porosity of the oxide coating

The process of formation of an oxide coating (strengthening and heat-insulating one) on the working surfaces of the piston head (piston bottom and grooves) using the method of micro-arc oxidation (MAO) is discussed. It is noted that during the oxidation of the piston head, the MAO process conditions will have a significant effect on the thickness and porosity of the oxide coating formed. The theoretical dependences of the influence of the electrical parameters of the microarc oxidation process conditions on the thickness and porosity of the oxide coating are presented. It has been found that the thickness of the oxidized layer will be directly proportional to the voltage and composition of the electrolyte, and the porosity is inversely proportional to the voltage and directly proportional to the current strength. It is shown that by varying the parameters of the oxidation conditions (current strength, voltage and process time), oxidized layers of the required thickness and porosity can be obtained.

The Effect of Anodization on the Mechanical Properties of AA6061 Produced by Additive Friction Stir-Deposition

This paper examines the impact of oxide coatings on the surfaces of feedstock material used for Additive Friction Stir-Deposition (AFS-D). The AFS-D is a solid-state additive manufacturing process that uses severe plastic deformation and frictional heating to build bulk depositions from either metallic rod or powder feedstock. Since aluminum alloys naturally form an oxide layer, it is important to determine the influence of the feedstock surface oxide layer on the resultant as-deposited microstructure and mechanical properties. In this study, three AA6061 square-rod feedstock materials were used, each with a different thickness of aluminum oxide coating: non-anodized, 10-micron thick, and 68-micron thick. Macroscale depositions were produced with these feedstock rods using the AFS-D process. Optical and electron microscopy showed that the two oxide coatings applied through anodization were efficiently dispersed during the AFS-D process, with oxide particles distributed throughout the microstructure. These oxide particles had median sizes of 1.8 and 3 μm2, respectively. The yield and tensile strengths of these materials were not measurably impacted by the thickness of the starting oxide coating. While all three feedstock material variations failed by ductile rupture, the elongation-to-failure did decrease from 68% to 55% in the longitudinal direction and from 60% to 43% in the build direction for the thickest initial oxide coating, 68 microns.