Sławomir Kaptacz

This study explores the influence of significant manufacturing parameters, i.e., peak current density and frequency, on the oxide coatings’ micromechanical and sclerometric properties. The parameter levels were determined using a full experimental design with two variables at three levels. Plasma electrolytic oxidation (PEO) was conducted on an ultralight LA141 magnesium alloy in an alkaline ternary electrolyte. Coating performance was characterized by measuring hardness (HIT) and Young’s modulus (EIT), as well as three loads significant to coating failure: L_c1, the initiation of Hertzian tensile cracks; L_c2, the initiation of cohesive coating failure; and L_c3, full delamination of the coating. Scratch testing was complemented by profilographic analysis to provide isometric surface images. Statistical analysis was then employed to ascertain correlations of process parameters with the developed mechanical and sclerometric properties.

The article discusses the effect of Plasma Electrolytic Oxidation (PEO) on the tribological properties of oxidelayers produced on the AZ31B magnesium alloy. The layers were formed using PEO (AC+DC) in an alkalineelectrolyte with a current density of 10 A/dm. The oxidation parameters (process time, cathodic voltage) wereselected based on a research plan. The tribological properties of the samples were tested on a T-17 tester in apin-on-plate test under technically dry friction conditions, using a pin made of PEEK-HPV polymer. The testsallowed the determination of the coefficient of friction, linear wear, and changes in the mass of the sampleand pin. Profilometric measurements were also made before and after the friction process. An increase in theoxidation time and cathodic voltage led to an increase in the thickness and roughness of the oxide layer. Thesample oxidized under the highest parameters exhibited the greatest thickness, as well as the highest amplitudeand Abbott–Firestone bearing ratio parameters. It was found that with increasing process time and cathodicvoltage, the coefficient of friction (μ) and polymer pin wear increased. Sample C, which had the highestprocessing parameters, showed the best tribological properties, with a coefficient of friction of 0.253 and a linearwear of 0.057 mm. Due to friction, a significant amount of opaque tribofilm was deposited on sample C, resultingin the highest mass wear of the pin (5.33 mg) and an increase in the mass of the sample by 0.74 mg.

The purpose of this work is to determine the possibility of modifying oxide coating with nickel in the catalyticprocess and to verify the tribological properties of the coatings as a result of such modification. The coatingswere made on the EN AW-5251 aluminum alloy by electrochemical method. Nickel dispersions were obtainedthrough thermochemical treatment of the coatings. Tribological tests were carried out in a combination ofcoatings with polymer, cast iron, and steel, in a reciprocating motion on the T-17 tester. The paper presentsthe results of tribological tests and roughness of AAO coatings modified with nickel, before and after thetribological test. The results of tribological tests were supplemented with SEM tests and statistical analysis.The tests showed the possibility of modifying the AAO coatings with nickel compounds, which, in the case ofa sliding combination of the modified coating with steel, causes a significant reduction of friction forces bothin the case of technically dry friction and friction with lubrication.

This manuscript presents the influence of manufacturing process parameters (peak current density, frequency, process time) on the micromechanical and sclerometric properties of oxide coatings. These parameters were selected based on Hartley’s experimental design, considering three variables at three levels. The coatings were produced on the AZ31B magnesium alloy using the plasma electrolytic oxidation (PEO) method. A trapezoidal voltage waveform and an alkaline, two-component electrolyte were used during the process. The micromechanical and sclerometric properties were assessed by measuring the hardness (H_IT) and Young’s modulus (E_IT) and determining three critical loads: Lc1 (the critical load at which the first coating damage occurred—Hertz tensile cracks within the scratch), Lc2 (the critical load causing the first cohesive damage to the coating), and Lc3 (the load at which the coating was completely destroyed). Scratch tests were supplemented with profilographometric measurements, which were used to generate isometric images. To identify the relationship between micromechanical and sclerometric properties and the manufacturing parameters, statistical analysis was performed. Research has demonstrated that the plasma electrolytic oxidation (PEO) process improves the micromechanical and adhesive properties of oxide coatings on the AZ31B magnesium alloy. The key process parameters, including peak current density, frequency, and duration, are crucial in determining these enhanced properties.

This paper presents the influence of plasma electrolytic oxidation parameters (peak current density, process time, pulse frequency) on the tribological properties and surface wettability of the produced coatings. The process parameters were selected in accordance with Hartley’s research plan for three input variables with three variable values. Oxide coatings were made on the AZ31B magnesium alloy using a trapezoidal voltage waveform and a two-component alkaline electrolyte. The tribological properties of the coatings were determined as a result of tribological tests carried out on the T-17 tester in reciprocating motion. The tribological partner for the coatings was a PEEK/HPV pin. As a result of tribological tests, the friction coefficient µ, the mass wear of the pin and the average change in sample mass were determined. The tests showed changes in both the friction coefficient and pin wear. Before and after tribological tests, profilographometric measurements of the coatings were performed. The tests allowed for the determination of roughness parameters and the load–bearing curve of the sample surfaces. Surface wettability tests were carried out by determining the contact angles.

This paper presents the results of tribological tests on WE43 and WE54 magnesium alloys with rare earth metals performed in linear reciprocating motion for four different material couples (AISI 316-L steel, silicon nitride—Si₃N₄, WC tungsten carbide, and zirconium dioxide—ZrO₂). Additionally, magnesium alloys were subjected to a complex heat treatment consisting of precipitation hardening combined with a deep cryogenic treatment. The study presents the effect of deep cryogenic treatment combined with precipitation hardening on the tribological properties of WE43 and WE54 alloys. Tribological tests revealed the most advantageous results for the magnesium alloy—AISI 316-L steel friction node. For both alloys tested after heat treatment, a nearly 2-fold reduction in specific wear rate has been achieved. Furthermore, microscopic examinations of the wear track areas and wear products were performed, and the wear mechanisms and types of wear products occurring in linear reciprocating friction were determined. Wear measurements were taken using the 3D profilometric method and compared with the results obtained from calculations performed in accordance with ASTM G133 and ASTM D7755, which were modified to improve the accuracy of the calculation results (the number of measured profiles was increased from four to eight). Appropriately selected calculation methods allow for obtaining reliable tribological test results and enabling the verification of both the most advantageous heat treatment variant and material couple, which results in an increase in the durability of the tested alloys.

The article presents the effect of anodizing parameters of the EN AW-5251 aluminum alloy on the thickness and roughness of Al₂O₃ layers as well as their wettability and tribological properties in a sliding combination with the T7W material. The input variables were the current density of 1, 2, 3 A/dm² and the electrolyte temperature of 283, 293, 303 K. The tribological tests were performed on the T-17 tester in reciprocating motion, in conditions of technically dry friction. The tests were carried out on a 15 km road with a constant average slip speed of 0.2 m/s and a constant unit pressure of 1 MPa. The measurement of the wettability of the layers was performed using the sitting drop method, determining the contact angles on the basis of which the surface free energy was calculated. The profilographometric measurements were made. The analysis of the test results showed that the anodizing parameters significantly affect the thickness of the Al₂O₃ layers. The performed correlation analysis also showed a significant relationship between the roughness parameters and the wettability of the surface of the layers, which affects the ability to create and maintain a sliding film, which in turn translates into sliding resistance and wear of the T7W material. The analysis of friction and wear tests showed that the layer with hydrophobic properties produced at a current density of 1 A/dm² in an electrolyte at a temperature of 283 K is the most favorable for sliding associations with T7W material.

The mechanical and tribological characteristics of the Ti-6Al-7Nb alloy were investigated within a wide range of temperature and time parameters of thermal oxidation. The hardness, H_IT, and indentation modulus, E_IT, of the alloy in question, with and without an anti-wear oxide layer, were determined. The tribological properties of sliding couples were studied under technically dry friction conditions, using a ball-on-disc tribometer. The test pieces were non-oxidized and oxidized Ti-6Al-7Nb alloy discs, and Al₂O₃, ZrO_2, and 100Cr6 balls were used as counter specimens. After thermal oxidation, the surface of the titanium alloy was characterized by a significantly higher hardness, H_IT (8–10 GPa), compared to the surface not covered with oxide layers (3.6 GPa). The study showed that the curvature of the loading segments increased with an increasing oxidation temperature, indicating a strong positive dependence of hardness on the thermal oxidation temperature. The value of the indentation modulus, E_IT, was also found to increase with the increasing oxidation temperature. The intensity of the tribological processes was strictly dependent on the oxidation parameters and the couple’s material (Al₂O₃, ZrO₂, 100Cr6). It has been shown that the thermal oxidation process makes it possible to control, within a wide range, the friction-wear characteristics of the Ti-6Al-7Nb alloy.

The article presents the results of an aluminum oxide layer doped with monolayer 2H tungsten disulphide (Al₂O₃/WS₂) for applications in oil-free kinematic systems. The results concern the test carried out on the pneumatic actuator operational test stand, which is the actual pneumatic system with electromagnetic control. The cylinders of actuators are made of Ø 40 mm aluminum tube of EN-AW-6063 aluminum alloy which is used in the manufacture of commercial air cylinder actuators. The inner surfaces of the cylinder surfaces were covered with an Al₂O₃/WS₂ oxide layer obtained by anodic oxidation in a three-component electrolyte and in the same electrolyte with the addition of tungsten disulfide 2H-WS₂. The layers of Al₂O₃ and Al₂O₃/WS₂ obtained on the inner surface of the pneumatic actuators were combined with a piston ring made of polytetrafluoroethylene with carbon (T5W) material and piston seals made of polyurethane (PU). The cooperation occurred in the conditions of technically dry friction. After the test was carried out, the scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis of the surface of the cylinder bearing surfaces and piston seals of the pneumatic cylinders was performed. The analysis revealed the formation of a sliding film on the cylinder surface modified with tungsten disulfide, as well as on the surface of wiper seals. Based on the SEM/EDSM tests, it was also found that the modification of the Al₂O₃ layer with tungsten disulfide contributed to the formation of a sliding film with the presence of WS₂ lubricant, which translated into smooth cylinder operation during 180 h of actuator operation. The cylinder with the unmodified layer showed irregular operation after approximately 70 h thereof.