Papers by Keyword: Tribology

Abstract: Cold forging and sheet‑metal bulk forming operations typically involve severe deformation, high contact pressures, and substantial surface enlargement. As highlighted in previous studies, friction behavior under these extreme conditions is governed by temperature, contact pressure, sliding velocity, and changes in the real contact area due to surface expansion. This work presents a newly developed linear sliding tribotester designed to characterize the friction response of metal sheets subjected to sheet‑metal bulk forming conditions. The testing procedure consists of two stages. In the first stage, the sample is compressed to intentionally modify and enlarge the initial contact surface, with the degree of surface expansion controlled by the specimen geometry. In the second stage, once the surface has been altered, frictional contact is generated between the sample and a sliding table, enabling the measurement of normal and tangential forces. These force measurements are subsequently used to determine the mean coefficient of friction. The results obtained constitute the first dataset toward the development of a multi‑scale friction model for sheet‑metal bulk gear forging. This model aims to incorporate the effects of extreme contact pressures, asperity flattening, and lubricant-related hydrostatic and hydrodynamic mechanisms.

Abstract: Experimental determination of the real contact area is essential for the development and validation of advanced friction models in sheet metal forming. However, existing experimental approaches are limited by the need for transparent counterfaces or third agents in the interface, high sensitivity to relocation errors, or unreliable assumptions about the contact shape. This study proposes a novel ex-situ method to determine the real contact area using topographical information from the original and deformed sheet surfaces. The approach identifies a minimum contact area with high confidence and reconstructs from it the full contact area. It provides the real contact area ratio, the contact topography and height distribution. The method is evaluated using results from normal load simulations based on the Pullen and Williamson model as the reference and is compared with other ex-situ methods from literature. Results demonstrate that the proposed method is robust against realistic relocation errors and yields more accurate contact area values than existing approaches. The method offers a reliable experimental tool for tribological analysis and friction modelling in sheet metal forming.

Abstract: Nickel coated steel is used in the industry to produce battery shells. These shells are typically produced in several process steps: drawing, redrawing and several ironing steps at high production rates. The nickel plated steel sheet is subjected to a large range of deformations andpressures. Sometimes scratches in the longitudinal direction of the shell (hairlines) occur, due to the build-up of particles on the tooling (i.e. galling). Cleaning of the tools will be necessary and will bring additional costs. In this paper, analyses are performed on tribological behaviour of nickel plated steel sheet with the focus on tool wear. Adhesive wear has been observed to be the main wear mechanism. The adhesive layer build up consists mainly of compacted particles (often in the shape of flakes) of nickel and iron. The Slider on Sheet Test (SOST) is found to be a relevant set-up to study tribological behaviour of nickel plated steels in battery production.

Abstract: In this study, the mechanical and tribological properties of 3 mol. % yttria-stabilized tetragonal ZrO₂ (3Y-TZP) prepared by spark plasma sintering (SPS) were investigated. Nanoindentation revealed a high hardness of 16.51 ± 0.86 GPa and an elastic modulus of 250 ± 8.8 GPa. The low scatter of these values provides strong evidence for a homogeneous, fine-grained microstructure. Vickers microhardness at a 5 N load was 1382 ± 14 and indentation fracture toughness (K_IC, Niihara) was 5.2 ± 0.03 MPa·m¹ᐟ², confirming the material’s high mechanical resilience. Dry reciprocating sliding against a SiC counterface exhibited a stable coefficient of friction (COF) of 0.37–0.39, with a slight decrease to 0.37 at 25 N load attributed to the formation of a thin protective tribolayer. Wear track depth increased from ~0.8 µm (5 N) to ~2.8 µm (25 N), and width from ~1.400 µm to ~ 1.600 µm, while the specific wear rate rose only marginally from 9.28 × 10⁻⁸ to 5.05 × 10⁻⁷ mm³/N·m, demonstrating excellent wear resistance. SEM/EDX analysis revealed predominant abrasive wear with microcracking, alongside tribochemical oxidation layers rich in SiO₂ and carbon that contribute to surface protection. Stabilization of the tetragonal phase and a fine-grained microstructure are key factors enabling the superior hardness, elasticity, and tribological performance of 3Y-TZP for applications demanding low friction and high wear resistance.

Abstract: Aluminum 7075 alloy has excellent mechanical properties and exhibits good ductility, strength, toughness, and fatigue resistance. The addition of oxide additives to cast Al7075 has also enhanced tribological properties apart from these properties. In this study, the tribological properties of cast Al7075 with the addition of 2.5% zirconium oxide (Zirconia) and titanium oxide (Titania), produced in a resistance melting furnace followed by die casting, were investigated. The wear test is conducted using a pin-on-disc wear testing machine, as specified by ASTM G99. The comparison is based on two independent process variables: a fixed sliding distance of 1000 m for all samples and applied load variations are 10, 20, 30, and 50 N with 500, 700, and 1000 revolution speeds. Using a scanning electron microscope (SEM), the wear surface morphology of the samples was analyzed, and the wear test results were compared. Further, it was found that oxides added samples showed less wear loss compared to as-cast Al7075 samples. The abrasion mechanism for as-cast Al7075 samples is identified as ploughing and deep wear tracks, while for Al7075 samples with Zirconia and Titania addition, it is characterized by delamination and shallow wear marks that show less wear.

Abstract: This study investigates the tribological behavior of composites based on Al₂O₃–ZrO₂ stabilized with 3 mol. % Y₂O₃ (ZTA – zirconia-toughened alumina), prepared using spark plasma sintering (SPS) technology. The composites were characterized in terms of microstructure, mechanical properties, and wear resistance in a dry ball-on-flat configuration. SEM analysis confirmed a homogeneous and fine-grained microstructure without porosity, with Al₂O₃ grain sizes of 200–400 nm and ZrO₂ grain sizes of 100–200 nm. Measurements revealed high Vickers hardness (1566.7 ± 133.6 MPa), fracture toughness (6.4 ± 0.29 MPa·m¹ᐟ²), nanoindentation hardness (25.94 ± 2.35 GPa), and Young’s modulus (365.9 ± 18.2 GPa). The coefficient of friction ranged from 0.40 to 0.53 depending on the load, and the specific wear rate was extremely low (4.81 × 10⁻⁷ to 5.08 × 10⁻⁷ mm³/Nm). Analysis of the wear track revealed predominantly abrasive wear without significant fragmentation or delamination. The results demonstrate that optimized microstructure, proper phase stabilization, and a high degree of densification enable the preparation of composites with an excellent combination of hardness, toughness, and tribological resistance. These materials are suitable for demanding applications in industry, energy, and biomedicine.

Abstract: The paper presents a new concept of a thermally sprayed composite coating obtained by mixing NiCrAl powder with chromium carbide Cr₃C₂ in an amount of approximately 30 wt.%. The aim of the research was to obtain a material combining the advantages of a metallic matrix and a ceramic phase, with increased resistance to wear and erosion. The plasma spraying (APS) process was carried out on a carbon steel substrate with variable technological parameters: arc current intensity (300/500/700 A) and hydrogen flow (4/8/12 NLPM), while maintaining the other conditions constant.The thickness, porosity, microstructure, chemical composition (using the EDS method), hardness, erosion resistance, and tribological wear of the coatings were evaluated. The results showed that the greatest thickness (approx. 150 µm) and lowest porosity (below 3 vol. %) were obtained at the maximum process parameters – 700 A and 12 NLPM. In turn, the thinnest and most irregular coating (approx. 70 µm) was obtained at the lowest hydrogen flow (4 NLPM), which was due to insufficient melting of the powder particles.Increasing the current intensity and hydrogen flow had a beneficial effect on all analyzed coating properties – especially hardness (up to 273.7 HV0.2), erosion resistance (the smallest mass loss of 0.007 g), and tribological wear resistance (the smallest volume loss of 2.925 mm³). A decrease in any of the parameters resulted in a deterioration of the layer properties. The optimal mechanical and structural properties of the NiCrAl + Cr₃C₂ composite coating were achieved at the maximum plasma spraying parameters: a power current of 700 A and a hydrogen flow rate of 12 NLPM.

Abstract: This study evaluates the impact of replacing natural sand (NS) with quarry waste sand (QWS) or recycled concrete sand (RCS) at varying substitution rates (0%, 25%, 50%, 75%, and 100%). The analyzed properties include Abrams cone slump, superplasticizer demand (SP), rheological and tribological parameters, mechanical strength, capillary water absorption, and shrinkage. The results show that QWS-based concrete exhibits better workability and requires less superplasticizer, whereas RCS-based concrete necessitates a higher admixture dosage. Both QWS sand and RCS sand significantly enhance the rheological and tribological properties of concrete Moreover, QWS sand provides higher mechanical strength than NS sand, with a strength gain of up to 16% at full replacement (100% QWS sand) at 90 days. Conversely, RCS sand reduces compressive strength by 28.6% at 28 days. and negatively affects porosity and capillary water absorption. However, these negative effects are mitigated when the RCS sand replacement is limited to 25%. QWS sand-based concrete exhibits slower shrinkage and reduced deformability compared to NS sand-based concrete. Predictive strength models were established based on experimental parameters, displaying a high correlation coefficient and a low root mean square error. Replacing NS sand with QWS sand or RCS sand reduced production costs, lowered carbon emissions, minimized waste, and preserved natural resources, offering a sustainable approach for concrete applications.

Abstract: In this work, an experimental methodology is presented for investigating the kinetics of competing oxidation and metal-plating processes that occur on friction surfaces under variable load conditions. The aim of the study was to determine the critical parameters for the transition between the formation of dissipative secondary structures (DSS) and metal-plating films (MPFs), as well as to evaluate the contact electrical resistance (CER) as an indicator of the structural state of the surfaces. A universal tribometer with adjustable load (0.2–40 MPa) was used to test friction pairs of steel 45 and bearing steel Shkh15, employing a vaseline oil as an inert lubricant and CIATIM-201 grease with 7% copper powder as a metal-plating additive. A clear correlation was observed between the CER, the friction coefficient (μ) and the wear intensity (I) across four operating modes. The maximum CER values (up to 40 Ω·cm²) were recorded in the DSS formation regime, whereas the minimum values (below 1 Ω·cm²) corresponded to the metal-plating regime. The results demonstrate that the structural-energetic approach enables effective diagnosis of the tribological state and that the CER parameter serves as an informative criterion for distinguishing between friction regimes.

Abstract: Lubricants are substances that minimize wear and friction for optimal performance and lower the likelihood of malfunctions. Over 95% of lubricants used today are made of non-renewable petroleum, which is being depleted and emitting emissions that are bad for the environment and people's health. The greatest substitutes are biolubricants, whose primary sources include edible and inedible oils that are generated from lipids and carbohydrates found in various animals, plants, and microbe sources, with the exception of Algae. An eco-friendly and sustainable resource for green lubricants, microalgae oil is vital to the lubricant business. Microalgae are photoautotrophs, meaning they grow quickly and can be grown multiple times a year with less energy needed. Because microalgae do not require agricultural land or climatic conditions to develop, they may also be produced in wastewater and saltwater. As a result, their production costs are also lower. Microalgae has exceptional chemical compositions, including significant levels of lipids, hydrocarbons, polysaccharides, and gelling properties. Microalgae are suitable for lubrication because they contain high amounts of saturated, mono-unsaturated, and polyunsaturated fatty acids, which give algae their good tribological, physiochemical, and rheological qualities and minimize friction. Molecular weight, viscosity, oxidation stability, thickening behaviors, friction coefficient, antiwear, antiseizure, thermal stability & characteristics, crystallinity, and rheology of polysaccharides as sustainable green lubricant are all covered in this review study about the lubricating properties of microalgae oil.