Search Results (66)

The paper shows the effect of using a lubricant in the form of an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), on the tribological properties of a hydrogenated diamond-like coating (DLC) doped with tungsten a-C:H:W. The coatings were deposited on 100Cr6 steel by plasma-enhanced chemical vapor deposition PECVD. Tribological tests were carried out on a TRB³ tribometer in a rotary motion in a ball–disc combination. 100Cr6 steel balls were used as a counter-sample. Friction and wear tests were carried out for discs made of 100Cr6 steel and 100Cr6 steel discs with a DLC coating. They were performed under friction conditions with and without lubrication under 10 N and 15 N loads. The ionic liquid BMIM-PF₆ was used as a lubricant. Coating thickness was observed on a scanning microscope, and the linear analysis of chemical composition on the cross-section was analyzed using the EDS analyzer. The confocal microscope with an interferometric mode was used for analysis of the geometric structure of the surface before and after the tribological tests. The contact angle of the samples for distilled water, diiodomethane and ionic liquid was tested on an optical tensiometer. The test results showed good cooperation of the DLC coating with the lubricant. It lowered the coefficient of friction in comparison to steel about 20%. This indicates the synergistic nature of the interaction: DLC coating–BMIM-PF₆ lubricant–100Cr6 steel. Full article

This article presents the results of tests on the functional properties of oxide layers (Fe₂O₃, Cr_1.3Fe_0.7O₃) produced on AISI 316L austenitic steel, which is susceptible to friction wear, using a new, simple, inexpensive, and environmentally friendly process conducted in air at three different temperatures (400 °C, 450 °C and 500 °C). Vickers microhardness tests showed that the process slightly increased hardness only at lower indenter loads, indicating a low thickness of the layers. The greatest increase in hardness was observed in the sample oxidized at the lowest temperature. Tests performed using an optical profilometer showed a tendency for surface roughness to increase with oxidation temperature. Low surface roughness, enhanced microhardness and a low coefficient of friction resulted in the steel oxidized at 400 °C exhibiting the lowest wear rate in the “ball-on-disc” test. The contact angle measurements for all tested samples indicated hydrophilic properties. Potentiodynamic tests showed a deterioration in the corrosion resistance of the steel after oxidation at 450 °C and 500 °C. Oxidation at 400 °C did not cause a significant decrease in pitting corrosion resistance, while an increase in polarization resistance and a decrease in corrosion current density were observed. An interesting phenomenon, requiring further research, is the greatest increase in hardness and wear resistance observed in the layer formed at 400 °C. Full article

Perfluorinated tetradecanoic acid was added as an additive to a base oil and tested under full film elastohydrodynamic (EHD) contact conditions between a steel ball and a steel disc. By varying key performance parameters, we aimed to assess the feasibility and limitations of perfluorinated carboxylic acids in reducing friction in lubricated contacts. The results demonstrate that the tested perfluorinated additive is effective in reducing friction when blended with a non-polar synthetic poly-alpha-olefin oil. However, no significant friction reduction was observed when the same additive was used in a slightly polar synthetic ester. The carboxylic acid functional group plays a crucial role in the observed friction-reducing effect. Adjusting the additive concentration further plays an important role in reducing friction. A concentration of at least 0.35 wt.% is required to achieve a notable friction reduction of approximately 10%. Increasing the concentration beyond this threshold continues to improve the friction-reducing effect. Conversely, increasing the contact pressure has a detrimental impact on friction reduction. The greatest reduction in friction—over 20% compared to the base oil—was achieved at the lowest contact pressure tested (0.69 GPa). Full article

PVD hard coatings improve the wear and frictional properties in metal cutting and, therefore, extend the lives of cutting tools. Cutting fluids, including the novel use of liquid carbon dioxide (LCO₂), are crucial for reducing tool wear and enhancing machining efficiency. This experimental research is focused on ball-on-disc wear tests of TiAlN hard coatings in environmental, N₂ and CO₂ atmospheres. In the latter case, the experiments were also performed by adding LCO₂ directly into the contact zone. In order to achieve the same temperatures as real cutting conditions, tests were performed at 250 °C, 500 °C and 700 °C, in addition to room temperature. Results show that the TiAlN coating had the highest wear rate in room-temperature tests, regardless of the atmosphere. The wear significantly dropped with the test temperature. It was the lower in the CO₂ atmosphere at all temperatures than in all gas-only atmospheres. When LCO₂ was introduced to the contact, the wear was at its highest at 500 °C, which is the opposite of all other gas-only atmospheres, where it was at its lowest. In all tribological LCO₂ tests, we noticed increased friction coefficient fluctuations. In all gas-only atmospheres, adhered material was observed on the wear tracks, but in LCO₂, wear debris was not detected either on the disk or on the ball. Full article

To avoid wear and tear of the slip ring due to electrical corrosion, the slip ring needs to undergo the running-in process under atmospheric conditions without current after assembly. To address the urgent demand for long-service capability space conductive slip rings in the aerospace field, the running-in behavior and failure mechanism between the AgCuNi alloy and Au-electroplated layer are investigated using a ball-on-disc tribometer in this paper. The results show that the transfer film composed of Au plays an important role in modifying the friction during the sliding process. With the accumulation of wear debris composed of Ag on the disc, the contact material of the friction pair changed from Au and Au to Au, Ag and Au, so the surface roughness of wear tracks increased. Finally, the transfer film broke, which made the layer fail. This paper reveals the key element failure mechanism that causes transfer film failure in the running-in contact area, which is used to reveal the friction behavior and failure mechanism of slip ring friction pair materials, and provides a basis for the selection of running-in parameters during the running-in process of slip rings before power-on operation. Full article

This article compares the rheological and tribological properties of three ionic liquids: Tributyl(methyl)phosphonium dimethyl phosphate 97%—MFCD, 1-Butyl-3-methylimidazolium hexafluorophosphate 97%—BMIMPF6, and 1-Butyl-3-methylimidazolium tetrafluoroborate 98%—BMIMBF4. Their density and kinematic viscosity at 20 °C and 40 °C were investigated, and tribological tests were carried out at the same temperatures with ball-on-disc contact. The test materials were made of 100Cr6 steel. A scanning electron microscope was used to image the wear tracks, while an EDS analyzer was employed to determine the chemical composition at the points of wear on the samples. A confocal microscope was used to analyze the geometric structure of the samples before and after the tribological tests. The results of the tests indicated that an increase in temperature reduced the dynamic viscosity of all the ionic liquids tested. At the same time, an increase in the MFCD and BMIMBF4 ionic liquid density and a decrease in the density of the BMIMPF6 ionic liquid were observed. The BMIMPF6 ionic liquid used for this study provided the lowest value of linear wear at both temperatures, ambient and 40 °C. However, for the BMIMBF4 ionic liquid, significant wear was observed for the tested discs and balls, with corrosive pitting on their surfaces. Full article

The aim of the study was to compare the hardness, coefficient of friction, and wear experienced by four different ceramic samples: 3Y-TZP zirconium oxide ceramics—Zi—Ceramill Zi (Amman Girrbach), 5Y-PSZ transparent zirconium oxide ceramics—Zol—Ceramill Zolid (Amman Girrbach), Sak—feldspathic ceramics—Sakura Interaction (Elephant), and Glaze (Amman Girrbach). The Vickers hardness of the samples was measured. Friction tests ball-on-disc were performed between the discs of four ceramics and a zirconia ceramic ball, then a premolar tooth as a counter-sample. The mass loss and the friction coefficients of the ceramic samples were determined. The tooth counter-samples were 3D scanned, and enamel attrition depths and mass were measured. The following hardness values (HV1) were obtained: 1454 ± 46 HV1 for Zi, 1439 ± 62 HV1 for Zol, 491 ± 16 HV1 for Sak, 593 ± 16 HV1 for Glaze, and 372 ± 41 HV1 for enamel. The mass losses of the teeth in contact with ceramics were 0.1 mg for Zi, 0.1 mg for Zol, 5.5 mg for Sak, and 4 mg for Glaze. Conventional and transparent zirconium oxide ceramics are four times harder than enamel and three times harder than veneering ceramics. Zirconia ceramics exhibit lower wear and a more homogenous, smoother surface than the other ceramics. Tooth tissues are subject to greater attrition in contact with veneering ceramics than with polished zirconium oxide ceramics. Full article

The paper presents the influence of the temperature of the sintering process on the microstructure and selected properties of boron carbide/TiB₂/SiC composites obtained in situ by spark plasma sintering (SPS). The homogeneous mixture of boron carbide and 5% vol. Ti₅Si₃ micropowders were used as the initial material. Spark plasma sintering was conducted at 1700 °C, 1800 °C, and 1900 °C for 10 min after the initial pressing at 35 MPa. The heating and cooling rate was 200 °C/min. The obtained boron carbide composites were subjected to density measurement, an analysis of the chemical and phase composition, microstructure examination, and dry friction-wear tests in ball-on-disc geometry using WC as a counterpart material. The phase compositions of the produced composites differed from the composition of the initial powder mixture. Instead of titanium silicide, two new phases appeared: TiB₂ and SiC. The complete disappearance of Ti₅Si₃ was accompanied by a decrease in the boron carbide content of the stoichiometry formula B₁₃C₂ and an increase in the content of TiB₂, while the SiC content was almost constant. The relative density of the obtained boron carbide composites, as well as their hardness and resistance to wear, increased with the sintering temperature and TiB₂ content. Unfortunately, the reactions occurring during sintering did not allow us to obtain composites with high density and hardness. The relative density was 76–85.2% of the theoretical one, while the Vickers hardness was in the range of 4–12 GPa. The mechanism wear of boron carbide composites tested in friction contact with WC was abrasive. The volumetric wear rate (Wv) of composites decreased with increasing sintering temperature and TiB₂ content. The average value of coefficient of friction (CoF) was in the range of 0.54–0.61, i.e., it did not differ significantly from the value for B₄C sinters. Full article

Typical lubricants behave in a non-Newtonian manner under conditions of high shear and high pressure, as is commonly observed in lubricated rolling/sliding contacts. To optimize and predict the friction therein, knowledge of the high-pressure rheological behaviors of lubricants and limiting shear stress (LSS) is essential. This study developed an approach for determining the LSS of lubricants based on friction mapping of rolling/sliding contacts, using a ball-on-disc traction machine. The main contribution lies in the introduction of a practical approach for the selection of a proper entrainment velocity for determining the LSS, with reduced thermal influences and near isothermal conditions. The proposed approach enables full film lubrication, while keeping the film as thin as possible to prevent excessive shear heating and, thus, thermal effects. The LSS of two lubricants, PAO40 and complex ester, has been measured at pressures ranging from 1.2 GPa to 1.7 GPa. A bilinear model has been used to describe the variation of LSS with pressure. The impact of entrainment velocity selection on the measurement of LSS is also discussed. Full article

In this paper, the authors investigated the impact of DLC coatings doped with tungsten (a-C:H:W) coatings obtained using plasma-assisted physical vapor deposition (PVD) on the properties of the 100Cr6 steel. The results of the 100Cr6 steel specimens with and without the coating were compared. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were used to observe the morphology of the coating surfaces and cross-sections and identify the elements in the coating composition. The contact angle of the investigated surfaces was measured with a tensiometer. Additionally, the effect of the coatings on the tribological properties of lubricated friction pairs was evaluated. Friction tests were performed on a ball-on-disc tribometer under lubrication with cutting fluid. The surface texture of the samples before and after the tribological tests was measured using a confocal profilometer. The results obtained from the tests and analysis allow for the conclusion that the use of DLC coatings a-C:H:W increases the hardness of 100Cr6 steel by three times. The values of the contact angles were indicative of surface hydrophilic characteristics. The tungsten-doped diamond-like coating under friction conditions reduced the coefficient of friction and wear. DLC coatings a-C:H:W lubricated with the cutting fluid improve the mechanical and tribological properties of 100Cr6 steel sliding surfaces under friction. Full article

Predicting the tribological behaviour in the secondary shear zone in the metal-cutting processes is considered a significant challenge in contemporary research. This work investigated the frictional performance in the secondary shear zone of a planing process using a modified ball-on-disc open tribometer. The values of the coefficient of friction (COF) were tracked between an AISI4140 + QT disc (chip) and a cemented carbide ball (cutting tool) coated with TiAlN under three contact pressures of 0.5, 1, and 2 GPa at a range of sliding speeds starting from 0.2 m/s to 1.6 m/s. The tests were conducted under both dry and lubricated conditions using three commercial cutting fluids of CSF 35 straight oil, Vasco 6000, and Zubora 67H emulsions. Also, the MWFs were tested for their rheological properties and wettability. The tribometer results validated the same COF trend as that in the actual metal-cutting experiments, particularly at 0.5 and 1 GPa in dry conditions. Moreover, Zubora 67H emulsion is proven to be the optimal choice due to it reducing the COF between the rubbing contacts by up to 78%. Furthermore, it showed the lowest contact angle and viscosity index, revealing its ability to easily penetrate, especially at higher temperatures, within the secondary cutting zone. Full article

30CrNi2MoVA steel demonstrates excellent performance, meeting the requirements of a crucial material for high-load structural parts. However, after experiencing high loads and thermal cycling, the material undergoes wear on its contact surfaces, resulting in a certain wear depth that determines its service life. Therefore, accurately predicting and evaluating the wear performance and wear depth of this material is of paramount importance. This study employs a combined approach of experimental and simulation methods. Initially, friction and wear tests were conducted to investigate the wear behavior of the 30CrNi2MoVA steel. The experimental results reveal a significant influence of thermal cycling temperature on the material’s wear resistance, with wear mechanisms primarily attributed to adhesive wear and abrasive wear. Subsequently, a ball-on-disc wear model was established. Based on experimental data, the modified Archard model was implemented as a user subroutine in finite element software (ABAQUS version 2020) to assess the material’s wear volume. The simulation results demonstrate a close agreement with the experimental wear depths. Furthermore, a fitting formula was developed to correlate the wear depth of the material with the number of wear cycles, enabling accurate wear depth prediction. This study provides theoretical support for enhancing the performance and extending the service life of 30CrNi2MoVA steel. Full article

The study presents the use of spatial imaging of the shape of the deformation formation area occurring at the point of contact between the burnished tool and the processed material surface in the burnishing process. In the analysis of changes in the shape of surfaces processed by ball and disc pressure burnishing, an integrated measurement station was used to measure surface stereometry (New Form Talysurf 2D/3D 120 by Taylor Hobson) and to carry out a series of axially shifted roundness measurements (Talyrond 365 by Taylor Hobson). The geometric parameters of the deformation zone determined in the direction of the circumference of the cylindrical surface (direction of the main movement) and in the axial direction (in the feed plane) are presented. The data obtained as a result of metrological measurements were analysed using specialized computer software. Full article

The present study focuses on investigating the influence of oil and solid body temperatures on elastohydrodynamic lubrication (EHL) film formation. Experimental and numerical simulation methods are employed to examine three heating methods: oil and ball heating, disc heating, and entire system heating. A preliminary comparison between the measured results and numerical simulations confirms the impact of heating methods on film formation while validating the availability of the numerical models. Further numerical analysis reveals that in the case of oil and ball heating, the temperature gradient induced by differences in solid body temperatures plays a more significant role in film formation compared to the conventional thermal-viscosity wedge effect caused by EHL film shear. This effect is further amplified at large sliding–rolling ratios and in steel–steel contacts. The overall film formation is primarily governed by the oil inlet temperature, whereas local film formation characterized by a dimple shape is influenced by both thermal gradient effects and thermal-viscosity wedge effects. This study provides valuable insights for selecting appropriate heating methods in experiments as well as understanding how temperature differences affect film formation in practical engineering. Full article

Experiments with changes in motion geometry can provide valuable data for engineering and development purposes, allowing a better understanding of the influence of tribological factors on the performance and service life of joints. The presented subject article focused on the experimental investigation of the influence of the geometry of the movement of the friction process on the change in the tribological properties of 30CrNiMo8 steel. The friction process was carried out without the use of a lubricant in contact with a steel ball of G40 material with a diameter of 4.76 mm. The steel ball performed two types of movement on the surface of the experimental material. The first method used was ball on disc, in which the ball moved reciprocally in an oval direction at an angle of 180° on a circumferential length of 35 mm at a speed of 5 mm/s. The second method consists of the same input parameters of the measurement, with the difference that the path along which the ball moved had a linear character. The load during the experiment was set at a constant value of 50 N with 1000 repetitions. The results show that with the ball on disc method, there was an increase in wear by 147% compared to the linear test method, which was approximately a coefficient of increase in wear of 2.468. EDS analysis pointed to the occurrence of oxidative wear that affected the resulting COF values, which were lower by 8% when using the ball on disc method due to a more uniform distribution of O and C on the surface of the friction groove where these elements acted as solid microlubricants. With the ball on disc method, defects in the form of microcracks occurred, which affected the reduction in the values of the depth of the affected area of microhardness. Full article