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A Ni–Cr–MoS 2 coating with trivalent Cr was prepared on the surface of the cylinder liner by the composite co-deposition method to modify its tribology performance. The effects of MoS 2 concentration on the properties of the coatings and tribological properties of cylinder liners were studied by surface detection methods and reciprocating wear tests. The results show that Ni–Cr–MoS 2 coating has a smaller grain size, higher micro-hardness, and greater coating thickness, compared with Ni–Cr coating. Doping by MoS 2 effectively reduces the friction coefficient of Ni–Cr coating from 0.142 to 0.107, the wear amount of coating decreases from 7.9 mg to 7.1 mg, and the scuffing time increases from 19 min to 56 min. It is found that the doping of MoS 2 provided more nucleation sites and promoted the deposition of ions, which resulted in the refined grain and thicker coating. The formation of solid lubrication film by MoS 2 during the wear process and more coating thickness are mainly responsible for the modification of the tribology performance of cylinder liners. This research provides a practical approach to prolong the service life of friction pairs. • The inclusion of MoS 2 significantly increased the Ni–Cr coating thickness. • The doping of MoS 2 increased nucleation sites and changed the coating structure. • The friction and scuffing properties of cylinder liner were significantly improved. • A solid lubrication film produced on the surface of composite coating by MoS 2. [ABSTRACT FROM AUTHOR]

Cashew Nut Shell Liquid (CNSL) has been explored in several applications within the sustainability principles and circular economy of agro-industrial product waste. To understand the anticorrosive and lubricant properties of CNSL solutions, a multi-faceted approach, incorporating electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for mild steel AISI 1012, stainless steel AISI 420 and Aluminium Alloy 6061. Electrochemical analyses reveal a positive impact of CNSL, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current, indicating effective corrosion inhibition for stainless steel and aluminium alloy. In mild steel, CNSL exhibits a mixed-type inhibition with efficiency increasing in correlation with oil concentration. The lubricating properties of CNSL are evident according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests. Tribochemical tests demonstrate a reduction in wear and an improvement in tribocorrosion behavior under sliding conditions. CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits. The concentration-dependent effects highlight the need for optimization in specific applications, particularly for passive materials. CNSL not only inhibits corrosion through film formation but also provides effective lubrication, reducing friction, wear, and chemical-mechanical degradation. This research contributes valuable insights to corrosion science. It proposes practical applications for CNSL in diverse industrial contexts, showcasing its potential as an environmentally friendly and sustainable solution for tribocorrosion challenges. • The influence of Cashew Nut Shell Liquid (CNSL) on the tribocorrosion behavior across three metallic alloys (mild steel, stainless steel, and aluminium) is explored. • Electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for AISI 1012, AISI 420 and AA6061. • CNSL exhibited a positive impact on corrosion inhibition for stainless steel and aluminium alloy, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current. • CNSL demonstrated lubricating properties according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests. • CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits. [ABSTRACT FROM AUTHOR]

The effect of surface roughness, contact pressure and lubrication on the onset of galling of aluminum 6082-T6 is studied with a pin-on-plate tribometer. The design of experiments involves pins with mean arithmetic roughness Ra equaled to 0.2, 0.35 and 0.6 μm, normal loads ranging from 5 to 600 N, and 4 different lubrications: without lubricant, with MoS2 dry lubricant, with pure mineral oil and with a highly chlorinated paraffin oil. Tests are performed at room temperature and are repeated three times. Experimental results show the great sensitivity of the onset of galling to the roughness and the beneficial effect of dry and liquid lubricants. The occurrence of galling is study by optical micrographs, by the analyses of the coefficient of friction, and by the use of finite element simulations. It comes that the variation of the coefficient of friction is not self-sufficient to detect the onset of galling. The finite element computations involves Wilson's lubrication model and Xue's damage model. Galling is assumed when finite elements near the contact area reach the critical damage Dc. This numerical approach leads to a good prediction of the onset of galling for the tests performed under constant normal load. For tests performed with increasing normal loads and various lubricants, the numerical prediction overestimate the sliding length before galling occurs. • Galling of the aluminium alloy 6082 is predicted by means of finite element computations. • Pin-on-plate tests are performed to study the effect of roughness, contact pressure and lubricant on galling. • Wilson's lubrication model is used to compute the friction stresses, and a damage criteria to detect the onset of galling. • Good agreements are obtained between the numerical predictions of galling and experiments. [ABSTRACT FROM AUTHOR]

This study presents a novel and non-destructive method for quantitatively analysing grease lubricated bearing wear by using X-ray microcomputed tomography (μCT). The efficacy of μCT to measure rolling contact wear via wear debris analysis was demonstrated, as was quantifying grease contamination and wear debris identification. Test rig experiments of grease lubricated spherical roller bearings, were performed to simulate rolling contact wear. Six grease samples were collected from two bearings at three different intervals to investigate wear progression. Results showed μCT measured wear volume increased exponentially with increasing bearing operation times. Grease cleanliness (particle counts per ml) worsened nonlinearly due to the exponential growth of wear debris over longer bearing operational times. Comparing the conventional ISO281 bearing assembly and operating condition assessment, a particle-count based method via μCT analysis provided a less subjective and dynamic assessment for quantifying grease contamination. Grease contamination was found to increase with longer operational timeframes due to the combination of wear debris growth and decreased lubrication film thickness. Finally, laminar, chunk and spherical wear particles, associated with rolling contact wear, were identified by the morphometric parameters measured by μCT. This study highlights the potential of μCT as a wear monitoring and grease quality assessment technique for railway bearing applications. • Microcomputed tomography is pioneered to measure wear in test rig bearings. • The proposed method is nondestructive and requires no sample manipulation. • The efficacy in wear measurement is proven through debris analysis in grease. • Quantitative analysis of 3D wear debris images provides wear mechanism assessment. • Grease contamination worsens with wear debris growth exponentially and lubricant film thinning. [ABSTRACT FROM AUTHOR]

The paper proposes a novel numerical framework for modelling of the pitting damage mechanism, based on the application of the three-layered residual control staggered phase-field algorithm. Proposed numerical framework can be applied to all contacting mechanical elements subjected to rolling contact fatigue, but in this paper, it is applied on gears. More precisely, gear teeth flanks subjected to the rolling-contact fatigue conditions are investigated, which consequently results in governing pitting mechanisms. Loading of the teeth flanks is imposed via moving load, with assumption of the full-film lubrication and pressure distribution according to the elastohydrodynamic lubrication theory, as well as Hertzian theory. The Coulomb's law is used to compute the friction force distribution. The numerical framework is embedded into finite element software ABAQUS via user subroutines. The validity of the proposed numerical scheme is tested by comparison to the examples from the literature. The main mechanisms of the pitting formation have been verified, i.e., surface- and subsurface-initiated pitting formation. Furthermore, an influence of the microstructure has been considered in the modelling of pitting phenomena. It has been demonstrated that the proposed numerical framework provides satisfactory results, and it is able to capture governing pitting mechanisms. • A new procedure for modelling of rolling contact fatigue problems based on phase field method is proposed. • New methodology is verified on problems of pitting formation on gear tooth flanks. • Loading is imposed via moving load, with a pressure distribution according to the elastohydrodynamic lubrication theory. • The material utilized is the nodular cast iron EN-GJS-400-18-LT exhibiting nonlinear elastoplastic behaviour. [ABSTRACT FROM AUTHOR]

Surface roughness is significant to friction and wear. However, the influence remains elusive, especially at the nanoscale. This study aimed to explore the effect of the nanoscale surface roughness on sliding friction and wear. For bearing steel tribo-pairs, the surface roughness can affect the lubrication state transition. The lower the surface roughness is, the easier it is to enter mixed lubrication and full film lubrication. Moreover, reducing the surface roughness can decrease friction and wear in mixed lubrication. At 94 mm/s sliding speed, as the surface roughness S q decreases from 769.7 nm to 21.1 nm, the average friction coefficient first remains unchanged and then decreases by 20%, while the wear rate decreases by 85%. However, further reducing the surface roughness may result in friction failure, raising friction and wear. At 10 mm sliding radius, about 20∼40 nm S q can lead to the minimal friction and wear. For the mechanism, as the surface roughness decreases, the asperity contact diminishes. Therefore, friction and wear decrease. However, when the surface roughness passes the critical point, asperities cannot fully accommodate the interfacial wear debris. Consequently, friction failure occurs. The findings may provide an enhanced understanding of the role of surface roughness in tribology. [Display omitted] • The surface roughness can affect the lubrication state transition. • Reducing the surface roughness can decrease friction and wear in mixed lubrication. • Too low surface roughness may result in friction failure, raising friction and wear. [ABSTRACT FROM AUTHOR]

Undeniably, advances in water-based nano-additives play a considerable role in energy conservation and pollution reduction accompanied by the resurgence of water-based lubricants. Graphitic carbon nitride quantum dots (g-CNQDs) have attracted remarkable attention in water-based lubricant additives owing to their strong designability, favorable mechanical property, and unique self-lubricating effect. Therefore, a series of different-sized g-CNQDs with good water dispersibility were expediently synthesized via a hydrothermal strategy and directly used as water-based lubricant additives. Tribological tests indicated that the tribological behaviors of the g-CNQDs-based additives displayed an obvious phenomenon of performance-dependent physical dimensions. With the introduction of g-CNQDs-based additives (1.0 wt%) into the water-based lubrication system, which friction-reduction, anti-wear, and load-supporting performances can be maximally increased by 45.5%, 94.0%, and 233.3%, respectively. Meanwhile, the long-term operating performance of the lubrication system can be promoted under high-load conditions. The formed tribo-film caused by tribo-chemical reaction integrated with the nano-lubrication effect of g-CNQDs collectively contributed to their good tribological performances. • Various g-CNQDs-based additives of water lubrication were synthesized. • g-CNQDs as additives have excellent anti-friction and anti-wear functions. • g-CNQDs-based additives displayed great performance-dependent physical dimensions. • g-CNQDs showed outstanding film-forming and nano-lubrication effects. [ABSTRACT FROM AUTHOR]

Floating ring bearing has the advantages of simple structure and high operating speed and is widely used in turbocharger and aero-engine. However, many harsh working conditions cause the floating ring bearing to produce starved lubrication and failures. Here, we investigated the starved lubrication characteristics of floating ring bearing via theoretical modeling and numerical simulation. We first established a theoretical model of starved-boundary lubrication based on the Reynolds equation for floating ring bearing. And meanwhile, an oil-film ratio coefficient is introduced into the theoretical model to reflect the degree of starved lubrication. We then analyzed the influence of inlet-boundary conditions (flow rate, oil-film thickness) on the starved-lubrication performance of floating ring bearings. The results showed that the flow rate obviously affects the bearing area of inside and outside oil film, and the oil-film ratio coefficient inside the bearing. When the oil supply is lower than 10 mL/min, the floating ring bearing is in a serious starved-lubrication state, and the oil-film area of bearing is reduced by 30%. The favorable oil supply flow rate can obviously improve the lubrication conditions, and also can predict the starved state of inner oil-film. Our study provides a theoretical basis for the fault detection of floating ring bearing. • Studied the mechanism of oil-starved lubrication on floating ring bearing. • Established model of oil-starved lubrication to calculate lubrication characteristics for floating ring bearing. • Calculated lubrication characteristics under different lubrication conditions. • Analyzed the influence of oil supply on bearing lubrication characteristics. [ABSTRACT FROM AUTHOR]

A 3D time-domain modelling approach is developed with the explicit finite element method to simulate transient meshing contact of gear pairs and the resulting wear. Taking a helical gear pair used in a locomotive as an example, the dynamic contact states of gear teeth are predicted for different speeds in consideration of actual geometries (including those of damaged teeth), time dependent torques, and structural and continuum vibrations of the gear system. The friction between mating teeth is taken into account by a non-Newtonian EHL friction model. A tiny time step of 4.5 × 10−8 s determined by conditional stability of the explicit time integration ensures the capture of transient effects. Based on detailed contact solutions during meshing, the dynamic wear on teeth is further calculated using an Archard wear model to predict tooth profile evolvement. Taking initial involute profiles and a speed of 120 km/h, the model is first validated for dynamic contact solutions. More results show that structural vibrations and worn profiles influence the dynamic meshing contact significantly, tooth wear increases as lubrication fails, and tooth pitting's influence is localized. This approach provides key load boundaries for detailed studies on mating gears, and may be employed for studies on tooth damages and as a reference for lumped parameter dynamic models of gear pairs. • A 3D time-domain approach developed for transient meshing contact of worn gears. • Normal and tangent contact solutions obtained in dynamics for teeth at any instant. • Tooth wear is calculated from transient contact solutions during gear meshing. • Influence of vibrations, worn profiles, pitting and lubrication failures identified. [ABSTRACT FROM AUTHOR]

Stern shaft deformation caused by ship maneuvering will lead to stern bearing lubrication failure and wear. Based on the displacement superposition method, the deflection equation of the stern shaft under the action of the interface force and the propeller load was established. The fluid-solid coupling model of the stern bearing was established by using the averaged Reynolds equation, the Greenwood-Tripp model, and the influence coefficient method. The model was experimentally validated. The influence of the shaft bending deformation caused by the propeller load change on the lubrication characteristics is discussed. The results show that the shaft bending deformation leads to the changes in lubrication characteristics along the axial and circumferential directions. Compared with the vertical load alone, the existence of horizontal propeller load will significantly reduce the minimum nominal oil film thickness and friction coefficient. Under hydrodynamic lubrication, the direction of horizontal load has little effect on friction coefficient. • The displacement superposition method is used to calculate the bending deformation of the propeller shaft. • A fluid-solid coupling model of marine stern bearing is established. • The friction coefficient of the oil-lubricated bearing were tested to verify the model. • The lubrication performance of stern bearing during the ship severe turning maneuver is discussed. [ABSTRACT FROM AUTHOR]

The fretting behaviour of AISI 52100 steel and low alloy steel under grease lubricated conditions is investigated. The friction behaviour is characterized by a high friction regime for the smallest displacement amplitudes below and next to the partial-slip transition whereas a low friction regime is stabilized above a threshold sliding amplitude when a lubricating tribofilm is generated in the interface. In order to quantify the influence of different contact parameters like surface roughness, contact size and contact geometry, a new fast simplified fretting methodology is introduced. This method allows scanning the entire fretting regime through a single experiment. An experimental comparison of smooth and rough surfaces shows that the effect of surface roughness influences the stability and the performance of the lubricating tribofilm. Experimental results obtained through changing the contact size of the cylinder-on-flat configuration permit identifying two contact size regimes. For small interfaces, the effective fretting sliding amplitude triggering the tribofilm activation is proportional to the contact size, whereas for large contacts this amplitude appears to be constant. The comparison with a punch-on-flat interface suggests that the lubrication activation is better captured by considering the peak pressure width rather than the nominal contact size. • Experimental study of surface roughness, contact size and geometry effects in a grease-lubricated fretting contact. • Introducing simplified variable displacement method to assess grease effects. • Lubrication activation is better described considering peak pressure width rather than nominal contact size. [ABSTRACT FROM AUTHOR]

Friction modifiers (FMs) are widely used in wheel-rail applications. This paper presents a method to analyze the starved elastohydrodynamic lubrication (EHL) of the wheel-rail surface coated with FMs. Combined with rough surface simulation techniques, starved EHL analysis and film thickness analysis, the pressure distribution and adhesion coefficient under different film thickness states are obtained. The effect of film thickness of the FM supply layers and surface roughness on the adhesion coefficient is studied. The adhesion coefficient increases with the decrease in the effective FM film thickness and increase in the surface roughness. Based on the subsurface stress model, the subsurface stress distribution is studied. Then the influence of FMs on the fatigue of wheel and rail is analyzed on the basis of the shakedown map. Finally, the fatigue index of rail is explored in starved EHL state. • A friction modifier (FM) starved EHL numerical model considering the effective film thickness was established. • Roughness and the effective film thickness could remarkably affect the lubrication state of contact zone. • The adhesion coefficient gradually increases as decreasing the effective film thickness. • With the increasing roughness, the lubrication of wheel/rail surface gradually fails. • The fatigue index will be increased as increasing the roughness and decreasing the effective film thickness. [ABSTRACT FROM AUTHOR]

The textured surface is one of the hotspots in the field of tribology research on reducing friction and wear. By calculating and optimizing the micro-texture structure, researchers designed and prepared textures with excellent tribological properties on the mechanical part surfaces. In this work, the tribological performance of 42CrMo matrix composite textured surfaces (CTSs) with different textured densities under grease lubrication was studied. The CTS was composed of 42CrMo alloys and SnAgCu-MXenes-Ti 3 C 2 (SACM). The results showed that when the textured density ρ of CTS was 36%, the friction coefficient (0.090) and wear rate (5.4 × 10−9 mm3N−1m−1) of counterpart ball could be respectively reduced by 75.7% and 38.6% compared with those of counterpart ball against the untextured sample. CTS could enhance the stability of friction system. Mxenes-Ti 3 C 2 wrapped by SnAgCu could form the lubricating layer containing sub-micron rollers on the worn surface, effectively reducing the friction and wear of samples under grease conditions. [Display omitted] • The composite textured surfaces (CTSs) were designed and prepared. • MXenes wrapped by SnAgCu could form sub-micrometer rollers in wear scar. • CTS exerted tribological enhancement function under starvation. • CTS could produce excellent synergistic effect with grease. [ABSTRACT FROM AUTHOR]

Nitrile butadiene rubber (NBR) is a water-lubricated bearing material that demonstrates excellent vibrational absorption and impact resistance; however, rapid wear under abnormal conditions is still a serious problem. Graphene (Gra) and carbon nanotubes (CNTs) are two types of carbon nanomaterials with different dimensions and excellent mechanical and friction properties. In this work, Gra and CNTs were used to fill the NBR, and a multifunctional friction and wear testing machine was used to study their impacts on the friction between NBR and ZCuSn10Zn2 under water lubrication conditions. The results indicate that both Gra and CNTs can effectively reduce the adhesion and the friction coefficient of NBR during the friction process. The two-dimensional lamellar structure of Gra is more likely to precipitate from the NBR matrix to generate a surface lubrication film, which can effectively reduce the friction coefficient. Both Gra and CNTs can prevent crack initiation and propagation in NBR during the wear process, thereby effectively reducing the wear of NBR. Compared with the two-dimensional structure of Gra, the one-dimensional linear structure of carbon nanotubes can "trap" the NBR molecular chains more effectively during the friction process, thus reducing the initiation and propagation of wear cracks and further improving the wear performance of NBR. • Effect of different dimensions of carbon nanomaterials on friction behavior of NBR. • Effect mechanism of two-dimensional graphene and one-dimensional carbon nanotubes on friction behavior of NBR. • NBR wear mechanism enhanced by two-dimensional graphene and one-dimensional carbon nanotubes. [ABSTRACT FROM AUTHOR]

The combination of texturing pretreatments and lubricant films was researched to improve the dry friction and wear performance of aluminium alloys. Three linear microtextures with different spacings were fabricated on the aluminum alloy substrates by ultrasonic surface rolling processing (USRP). The surface characteristics of different microtextures, such as micromorphologies, hardnesses, and wettability, were tested. PTFE/PPS lubricant films were prepared onto the textured surfaces by electrohydrodynamic atomization (EHDA), and micromorphologies of the films were observed. The friction and wear performance of aluminum alloy substrate and the films with texturing pretreatments were tested by ball-on disk reciprocating sliding dry friction experiments, and the countball material was 316L steel. The test data indicated that all films effectively reduced the friction coefficient of the substrate surface, and among them, the film sample URTC100 with a combination of 100 μm spacing texture and PTFE/PPS film exhibited the best effect of anti-wear while dry reciprocating sliding. Compared to the unpretreated film sample, URTC100 increased the wear life by 10% and reduced the wear track width and adhesion width by 35% and 25%, respectively. • Ultrasonic surface rolling processing was used to prepare surface textures. • Electrohydraulic atomization was used to fabricate PTFE/PPS lubricant films. • The above two methods were synergistic on dry tribological property improvement. [ABSTRACT FROM AUTHOR]

Double helical gears are widely applied in the aviation, marine and energy equipment, and generally required to be modified as the crowned since the machining error and assembling error of the gear drive are inevitable. The crowned gears usually operate in point contact mixed elastohydrodynamic lubrication (EHL), and adhesive wear has been one of the most prominent problems, but few previous researches were focused on this problem. In this work, a wear life prediction model of crowned double helical gears in point contact mixed EHL is proposed. The tooth profiles of the crowned gears are obtained according to the generating principle, and the load is attained in consideration of multi-tooth pairs contact. The contact pressure is derived from Hertzian elastic contact theory and load sharing concept, and the sliding distance is determined by a generalized model. Then, the wear rate in point contact mixed EHL is evaluated by extending the Archard theory to lubricated case, and the extended Archard's wear model is used to formulate the gear tooth wear. Moreover, the wear life prediction model which takes account of rotation speed and input torque is established, and the influences of surface roughness and crowned amount on the wear life of the crowned gears are further studied. Results show that surface roughness has a great influence on the wear life at different rotational speeds, while input torque has a great influence on the wear life at different crowned amount. It indicates that the wear life of the crowned double helical gears can be improved by reasonable matching lubrication, modification and working parameters. • A wear life model is developed for crowned double helical gears in point contact mixed EHL. • Surface roughness has a great influence on the wear life at different rotational speeds. • Input torque has a great influence on the wear life at different crowned amount. • Lubrication, modification and working parameters optimization is beneficial for wear life. [ABSTRACT FROM AUTHOR]