Search Results (628)

Slide burnishing (SB) is a cheap and effective method for improving the surface integrity (SI) and operational behaviour (wear, fatigue, corrosion) of metal components. As its name suggests, SB is implemented through tangential sliding friction and is based on severe plastic deformation of the surface. The review presented here is dedicated to SB implemented using a non-diamond-based deforming element and aims to systematise the achievements from recent decades regarding SB’s effects on the SI, fatigue, wear and corrosion behaviour of metal components. Depending on the burnishing conditions (lubrication, cooling, assisting and their main effects on the treated surface), and based on the difference between the concepts of method and process, a classification of the types of SB processes was made based on the SB method—that is, conventional, sustainable, minimum quantity lubrication-assisted, special, hybrid and combined processes involving SB. Based on this classification, a critical analysis was conducted, viewed through the prism of correlations between the SB, SI and operating behaviour. With sustainability issues becoming increasingly relevant across all industries, more attention is being paid to sustainable SB processes. Because the finite-element method is a powerful and inexpensive tool that can be applied to the analysis of burnishing processes, we used it to build adequate finite-element models of SB processes. At the end of the paper, we outline avenues for future research on SB. Full article

In this study, the tribological compatibility of ZrO₂-nanofiber-strengthened Al-matrix composites with graphene nanoplatelets (GNPs)-derived surface film acting as a solid lubricant was investigated. The substrate materials prepared by Spark Plasma Sintering (SPS) included the pure aluminum monolith (reference material) and two Al–ZrO₂ nanocomposites with either 1 or 3 wt.% of ZrO₂ nanofibers. The GNPs-derived solid lubricant films were dry mechanically burnished into the metallographically polished surfaces. The durability of these burnished films was evaluated by performing tribological friction experiments using a ball-on-disk method. Thus, a friction load capacity of GNP-derived tribofilms on the substrate materials and its effect on the coefficient of friction (COF) were evaluated. The results showed that the films burnished on the surfaces of Al–ZrO₂ nanofiber composites were more resistant to much higher loads than films burnished on monolithic aluminum. The obtained findings indicated that ZrO₂ nanofiber protrusions likely stabilize a GNP-derived carbon tribolayer on the polished composite surfaces. As a result, the reinforcement of aluminum with ceramic nanofibers led also to a significant reduction in COF. The highest improvement of tribological performance was observed for the Al–ZrO₂ nanofiber composite with 1 wt.% ZrO₂ nanofibers. The increase of ZrO₂ nanofibers up to 3 wt.% was no more efficient due to nanofiber clustering leading to lower stability of the carbon friction film. Our objective was to isolate the role of the aluminum substrate, specifically, ZrO₂ nanofiber protrusions in the formation and retention of a GNP-derived carbon tribofilm under room-temperature, ambient-air dry sliding. Full article

With the increasing demand for energy conservation and emission reduction in the automotive industry, optimizing the performance of cylinder liner and piston ring pairs in engines has become crucial. Aluminum–silicon alloy cylinder liners, known for their lightweight and excellent thermal conductivity, have emerged as a new trend in cylinder liner materials. Given the relatively moderate hardness of Al-Si alloys, judicious selection of piston rings is imperative to ensure optimal performance. This study investigates the tribological properties of aluminum–silicon alloy cylinder liners paired with CKS and DLC piston rings. The surface morphology and hardness of the test materials were characterized, and reciprocating friction and wear tests were conducted, using a tribometer to simulate operating conditions. The friction coefficient and wear volume were used as indicators to evaluate the tribological properties of the piston rings. The results show that, when the aluminum–silicon alloy cylinder liner was paired with a DLC piston ring, the friction coefficient was 27.82% lower, and the wear volume of the cylinder liner was 83.52% lower, compared to pairing with a CKS piston ring. When paired with a CKS piston ring, wear was exacerbated because silicon particles were easily dislodged to form abrasive particles. This particle detachment is mainly caused by the collision between the fine ceramic particles embedded in the CKS coating and the silicon particles (≤5 μm) uniformly distributed in the Al-Si alloy cylinder liner during the sliding process. The DLC piston ring, containing both sp² and sp³ hybridized carbon–carbon bonds, combined excellent lubrication properties with high hardness, resulting in minimal wear on both the cylinder liner and piston ring. Specifically, the DLC coating has a hardness of 2300 HV_0.3, which is 2.42 times that of the CKS piston ring (950 HV_0.3); the sp³-hybridized carbon in the DLC coating enhances its wear resistance to resist scratching from silicon particles in the cylinder liner, while the sp²-hybridized carbon forms a graphite-like transfer layer at the friction interface to reduce frictional resistance. In conclusion, the aluminum–silicon alloy cylinder liner paired with a DLC piston ring exhibits superior tribological properties. Selecting an appropriate piston ring can significantly enhance the tribological properties of the cylinder liner–piston ring pair, thereby extending the engine’s service life. Full article

Oils with low-friction performance are essential to meet the evolving requirements of the modern industry. Except for the viscosity, there is still a lack of a high-pressure rheological parameter that can quantitatively compare the friction performance of base oils. This study investigated the frictional behavior of six types of base oils with identical viscosity at 40 °C—paraffinic mineral oil 500N, naphthenic mineral oil, polyalphaolefin (PAO), oil-soluble polyether, ester oil, and alkyl naphthalene. Stribeck and traction curves were measured. The limiting shear stress (LSS) has been proposed and modeled for the quantitative comparison of the friction behavior of the base oils at high pressures (1.2–1.7 GPa). Results indicate that the PAO exhibits the lowest friction coefficient. Additionally, the LSS of all tested oils has a linear relation with the average contact pressure (R² > 99%), suggesting that the LSS at different mean contact pressures can be predicted using a linear LSS-pressure fitting model. This work contributes to providing fluid rheological models for the quantitative EHL friction prediction and provides guidance for choosing low-friction base oils for EHL-lubricated rolling/sliding contacts. Full article

This article comprehensively reviews the tribological behavior of a Ti-6Al-4V alloy manufactured via electron beam powder bed fusion (EB-PBF), an additive manufacturing process for aerospace and biomedical applications. EB-PBF Ti-6Al-4V demonstrates wear resistance that is superior or comparable to conventional Ti-6Al-4V. The reported average friction coefficient ranges between ~0.22 and ~0.75 during sliding wear in dry and lubricated conditions against metallic and ceramic counterparts when loading 1–50 N under varied surface and heat treatment conditions, and between 1.29 and 2.2 during fretting wear against EB-PBF Ti-6Al-4V itself. The corresponding average specific wear rates show a broad range between ~8.20 × 10⁻⁵ mm³/Nm and ~1.30 × 10⁻³ mm³/Nm during sliding wear. Lubrication reduces the wear rates and/or the friction coefficient. Wear resistance can be improved via machining and heat treatment. Wear anisotropy is reported and primarily attributed to microhardness variations, which can be mitigated through lubrication and post-processing. The effects of applied load and frequency on EB-PBF Ti-6Al-4V are also discussed. The wear resistance at elevated temperatures shows a mixed trend that depends on the counterpart material and the testing methods. Wear mechanisms involve oxide tribo-layer formation, abrasive wear, and adhesive wear. Current limitations, future research directions, and a standardization framework are also discussed. Full article

During drilling in complex formations, the sliding bearings of roller cone bits are continuously subjected to low-speed, heavy-load, and boundary lubrication conditions, under which adhesive failure readily occurs, severely limiting drilling efficiency. To enhance their wear resistance, a bionic texture inspired by shark denticles was designed and compared with conventional rectangular and circular textures. An equivalent pin–disk contact model was established based on Hertzian contact theory, and tribological experiments were conducted under typical formation conditions using a friction and wear testing machine. The friction coefficient, friction torque, and wear volume of different textures were measured under both lubricated and dry contact conditions, and the underlying mechanisms were elucidated through three-dimensional surface morphology analysis. The results show that the shark denticle-inspired texture reduced the friction coefficient and wear volume by 33.3% and 35%, respectively, under lubrication, while suppressing debris intrusion at the frictional interface under dry contact, thereby providing a degree of surface protection. This study offers theoretical guidance and experimental evidence for advancing the engineering application of bionic tribology in the petroleum industry. Full article

MoSe₂ is considered one of the most promising low-friction coatings for tribological applications due to its exceptionally low sensitivity to air humidity. However, knowledge of its tribological performance, especially in combination with oil lubrication, is still very limited. In this study, the tribological properties of MoSe₂ coatings deposited by magnetron sputtering were investigated using a reciprocating pin-on-flat tribometer against steel balls under both dry and PAO4-lubricated sliding conditions. The worn surfaces of the coatings and their counterparts were analyzed by profilometry, Raman spectroscopy, and scanning and transmission electron microscopy. Under dry lubrication, the coatings exhibited low friction (0.054), which was attributed to the combined effects of a lubricious transfer layer forming on the steel ball and a crystalline MoSe₂ tribolayer in the coating wear track, with MoSe₂ basal planes aligned parallel to the sliding direction. In contrast, under oil lubrication, the absence of a transfer layer on the ball and a crystalline tribolayer in the coating wear track resulted in higher friction (0.101). This high friction was accompanied by a 27% reduction in the wear rate due to the presence of PAO4 at the sliding contact, which served as a sealant and protected the coating from oxidation. Full article

The range of lubricant applications has broadened to include multiple sectors, aiming to optimize the operational efficiency of mechanical systems. Given their adaptable friction-reducing properties, lubricants have recently been incorporated into energy harvesting technologies such as triboelectric nanogenerators (TENGs). In such devices, lubricants are essential for mitigating wear, facilitating heat dissipation, eliminating contaminants, and prolonging the service life of mechanically actuated energy harvesters. Notably, emerging developments in sliding and rotational-mode TENGs leverage lubricants to improve electrical output while reducing interface degradation. However, despite significant potential, TENGs still face inherent challenges, including interface friction and energy losses from air breakdown. Recent research indicates that these drawbacks can be effectively addressed by the intentional use of polymer-based lubricants, which contribute to maintaining micro/nanostructured surfaces and minimizing air breakdown, thereby enhancing charge storage capability and increasing device robustness. This review systematically examines the categories, physicochemical attributes, and operational roles of polymeric lubricants used in TENG technology. It underscores their combined function is both primary and support materials to augment triboelectric efficiency. In addition, the article assesses how different lubricants impact device performance and durability, providing a critical analysis of their suitability based on the operational benchmarks of lubricant-embedded TENG configurations. Full article

Self-lubricating polymer composites based on polydicyclopentadiene (PDCPD) were reinforced with carbon nanomaterials to evaluate the effect of filler type and loading on their mechanical and tribological performance. Four carbon forms were introduced: carbon nanotubes (0.3 and 0.5 wt.%), carbon fibers (5 and 10 wt.%), flake graphite (5 and 10 wt.%) and dusty graphite (5 and 10 wt.%). Tensile tests showed that carbon fibers—and graphite-filled matrices reached ~50 MPa tensile strength, while the addition of carbon nanotubes resulted in a reduction in strength by half compared to the pure resin, indicating poor compatibility of carbon nanotubes with the matrix. The highest compressive strength, ~90 MPa, was obtained for PDCPD containing 5 wt.% carbon fibers. Tribological behavior was evaluated in a pin-on-disk configuration under dry sliding. All fillers lowered the coefficient of friction; the most pronounced, three-fold reduction was achieved with both graphite variants. The combined high load-bearing capacity and greatly reduced friction of the graphite and carbon fibers modified systems highlight their potential as self-lubricating bearing materials capable of replacing conventional metal or oil-lubricated components. Full article

In this study, we investigated the tribological properties of various additives (lubricity, friction modifiers, anti-wear and extreme pressure) in a highly volatile paraffinic base oil formulated for stamping applications, using a newly developed methodology for tribological testing. The investigation focused on the short-term (10 cycles) and long-term (10,000 cycles) effects of the different additive mixtures on friction and wear behaviour. It was found that the performance of the additive mixtures evolves with sliding time, which is due to changes in contact conditions: the transfer of the Fe film from the steel sheet to the WC-Co surface increases the contact area, which in turn leads to a significant reduction in contact pressure and changes the activation of tribofilm formation. The presence of tribofilms influences the amount and size of the contact area and reduces the adhesion between the contact surfaces. Among the conventional additives, sulphurised additive mixtures show stable performance under both short and long-term conditions, while more aggressive chlorinated additive mixtures perform well in the short term, but their performance decreases with prolonged sliding. Importantly, the additives with a decreasing environmental impact outperformed the conventional additives under long-term conditions: the less harmful phosphorus-based mixture outperformed the sulphurised mixtures in terms of wear properties, while the performance of environmentally acceptable polyol ester was particularly encouraging, exhibiting the lowest friction coefficient (~0.11, compared with ~0.12 for S-oil and 0.14 for S-ester) and the second lowest wear coefficient (~1.1 × 10⁻¹ mm³/Nm compared with ~1.5 × 10⁻¹ mm³/Nm for S-ester). Overall, the polyol ester reduced the coefficient of friction by approximately 8 to 21% compared to sulphurised additive mixtures, and its wear coefficient was also about 27% lower. Full article

Magnesium alloys are widely used in automotive and aerospace applications due to their light weight but suffer from poor tribological performance. This study investigates the effects of base oil (SAE 5W-30) with 100% hBN, 100% ZnO, and various ratios of hBN/ZnO hybrid nanoparticles on the tribological performance of AZ91D magnesium alloy. Pin-on-disk tribometer tests were conducted on AZ91D magnesium alloy under loads of 10–60 N and a sliding distance of 1000 m. Dry sliding produced the highest coefficient of friction (COF, ~0.30) and the greatest wear. Base oil lubrication reduced COF to ~0.14 and improved wear resistance by more than 50%. The 100% hBN nanolubricant provided the lowest wear and a COF of ~0.114, while the 75hBN/25ZnO hybrid achieved the lowest COF (~0.110) with wear values close to hBN. Surface analyses confirmed that hBN formed a lamellar tribofilm that minimized metal-to-metal contact, and ZnO contributed to the formation of load-bearing oxide layers that enhanced surface stability. Overall, the results demonstrate that hBN and ZnO, in single or hybrid form, can significantly reduce friction and wear, showing strong potential for applications in automotive, aerospace, defense, and industrial systems. Full article

When exposed to high contact pressure and shear conditions, the sliding and/or rolling contact interfaces of moving mechanical systems can experience significant friction and wear losses, thereby impairing their efficiency, reliability, and environmental sustainability. Traditionally, these losses have been minimized using high-performance solid and liquid lubricants or surface engineering techniques like physical and chemical vapor deposition. However, increasingly harsh operating conditions of more advanced mechanical systems (including wind turbines, space mechanisms, electric vehicle drivetrains, etc.) render such traditional methods less effective or impractical over the long term. Looking ahead, an emerging and complementary solution could be tribocatalysis, a process that spontaneously triggers the formation of nanocarbon-based tribofilms in situ and on demand at lubricated interfaces, significantly reducing friction and wear even without the use of high-performance additives. These films often comprise a wide range of amorphous or disordered carbons, crystalline graphite, graphene, nano-onions, nanotubes, and other carbon nanostructures known for their outstanding friction and wear properties under the most demanding tribological conditions. This review highlights recent advances in understanding the underlying mechanisms involved in forming these carbon-based tribofilms, along with their potential applications in real-world mechanical systems. These examples underscore the scientific significance and industrial potential of tribocatalysis in further enhancing the efficiency, reliability, and environmental sustainability of future mechanical systems. Full article

This study investigates the tribological performance and wear mechanisms of graphite and polydopamine/graphite (PDA/graphite) coatings on stainless steel under dry sliding conditions. While graphite is widely used as a solid lubricant, its poor adhesion to metal substrates limits long-term durability. Incorporating an adhesion-promoting PDA underlayer significantly improved coating lifetime and wear resistance. Tribological testing revealed that PDA/graphite coatings maintained a coefficient of friction (COF) below 0.15 for over seven times longer than graphite-only coatings. High-resolution scanning electron microscopy, SEM, and profilometry showed that PDA improved coating adhesion and suppressed lateral debris transport, confining wear to a narrow zone. Surface and counterface analyses confirmed enhanced graphite retention and formation of cohesive transfer films. Raman spectroscopy indicated only modest changes in the D and G bands. X-ray Photoelectron Spectroscopy, XPS analysis, confirmed that coating failure correlated with the detection of Fe and Cr peaks and oxide formation. Together, these results demonstrate that PDA enhances interfacial adhesion and structural stability without compromising lubrication performance, offering a strategy to extend the durability of carbon-based solid lubricant systems for high-contact-pressure applications. Full article

Due to their excellent mechanical stability, chemical stability, and environmentally friendly properties, ceramic materials have received extensive attention for years. Meanwhile, ionic liquids (ILs) have been found to effectively enhance tribological properties when applied as lubricants, which has become a distinctive example of their wide exploration. Here, three novel proton-type ionic liquids containing different polar groups were designed and synthesized as pure lubricants for use on different ceramic friction couples (silicon nitride–silicon nitride, silicon nitride–silicon carbide, and silicon nitride–zirconium oxide contacts), and their lubrication effect was evident. The results indicate that the adsorption behavior and frictional characteristics of different polar groups on a ceramic friction interface differ, largely depending on tribochemical reactions and the formation of a double electric layer on the interface between the ILs and ceramic substrates, without obvious corrosion during sliding. The friction coefficient is reduced by more than 80%, and this excellent anti-friction effect demonstrates that the constructed ionic liquid–ceramic interface tribological system shows good application potential. Based on the analyses of SEM, EDS, and XPS, the tribochemical reaction on the sliding asperity and the film-forming effect were identified as the dominant lubrication mechanisms. Here, the high lubricity and anti-wear performance of ILs containing phosphorus elements on different ceramic contacts is emphasized, enriching the promising application of high-performance ILs for macroscale, high-efficiency lubrication and low wear, which is of significance for engineering and practical applications. Full article

The present study aims to examine the tribological and mechanical integrity of AISI 316/420 stainless steel tribosystem under boundary lubrication with artificial seawater for application in a marine environment. The tribological performance was evaluated through sliding friction tests using a ball-on-disc configuration, at contact pressures ranging from 520 MPa to 1400 MPa. The influence of working contact pressure on the kinetic friction coefficient (µ_k), wear rate (K), and worn surface damage was studied. Their interaction with the corrosive medium was evaluated using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses to investigate the wear mechanisms. Microhardness testing was also employed to assess the effect of friction and wear on the mechanical properties of the tribosystem. The results showed that friction and microhardness increased with contact pressure, while the wear rate decreased due to strain hardening. The wear mechanisms included abrasion, adhesion, delamination, and localized oxidation. This study offers new perspectives on the tribological response of stainless steel materials in marine engineering systems, providing valuable insights for material selection and design in corrosive and high-load applications. Full article