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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]

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]

Determination of wear rate in spur gears requires treatment of the mixed elastohydrodynamic lubrication problem along the gear's line of action (LoA). For this purpose, a procedure is developed to predict the film thickness, traction coefficient and the wear rate with provision for the interactions between the surface asperities of the gear's teeth at each point on LoA. The results reveal that the surface finish has a more pronounced influence on the wear rate compared to the traction coefficient. The wear results are also compared to those obtained by an engineering approach that utilizes an estimate of the contact flash temperature with reasonable accuracy. Also investigated is the effect of starvation on the wear rate for applications where the inlet is not fully flooded. The results show that wear rate can be enormously large depending on the degree of starvation. [ABSTRACT FROM AUTHOR]

Friction, wear and plastic deformation of copper (Cu) and α/β brass were studied under lubrication conditions. Hardness and microstructure of surface layers were evaluated. The friction properties were presented by Stribeck curves. The friction coefficient and wear of brass were significantly larger in comparison to Cu. The critical load of transition from the elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) was two times lower for brass. Superplastic deformation of α-phase grains in brass is appeared under friction in BL, whereas plastic deformation localized at thin surface layers is observed for Cu. Intragranular sliding in α-phase is accompanied with the formation of shear bands and many pores coalesced to cracks. Thickness of the wear particles of brass is close to the width of shear bands. The deformation hardness of brass is significantly higher in comparison to Cu rubbed in the BL region. [ABSTRACT FROM AUTHOR]

Abstract: The continuum damage mechanics (CDM) approach in conjunction with the load sharing concept is applied to predict steady state lubricated line-contact wear. Empirical formula for the maximum contact pressure in dry rough contact is employed together with the lubricant film thickness equation to estimate the portions of the load carried by the asperities and the lubricant. Effect of contact temperature on wear is also included using a simplified thermo-elastohydrodynamic analysis in conjunction with fractional film defect concept. While most wear models require experimental calibration, current study attempts to predict wear purely based on numerical simulation. The proposed methodology is quite fast and easy to implement for practical engineering applications. Comparison of numerical calculations with available experimental wear data show very good agreement. [Copyright &y& Elsevier]

Abstract: This paper proposes an experimental methodology for the analysis of the lubrication regime and wear that occur between vanes and pressure ring in variable displacement vane pumps. The knowledge of the lubrication regime is essential for the improvement of the performance of high pressure vane pumps by reducing wear, increasing the volumetric efficiency and decreasing maintenance costs. Tests using pressure rings of different materials were carried out in order to identify the best material in terms of wear and friction. The proposed methodology is based on Archard's law and takes advantage of wear experimental measurements, an empirical model for the estimation of contact pressure forces and hardness standard tests. The results of the analysis state that low wear and reduced friction can be obtained if elasto-hydrodynamic lubrication between vanes and pressure ring is established. Results have been also verified by an analytical elasto-hydrodynamic model. [Copyright &y& Elsevier]

The friction and wear behavior were studied for three materials typically found in industrial bearing applications: a Sn-based Babbitt, polytetrafluoroethylene (PTFE) and a polyether ether ketone (PEEK) composite. Test conditions were unidirectional sliding with a ball-on-disc geometry where the counter surface material was a 440C stainless steel ball (6.35 mm dia.). The tests were also in the presence of a lubricant, ISO46 oil, with the sample and contact submerged throughout the test. The relative effects of load and sliding velocities on the wear rates were assessed by means of regression analysis. Connections between wear and the materials mechanical properties, which were measured by instrumented indentation, were also made. The ranking of wear performance of the materials correlated best to the ratio of H/(E*)0.447, where H is the test material's hardness and E* is the reduced modulus for the contact. The power applied to the reduced modulus is that used in previous studies to estimate the oil film thickness for an isoviscous, elastic lubrication regime. • Friction and wear rates of bearing materials are measured in oil-lubricated sliding against a stainless steel ball. • The mechanical properties were assessed by instrumented indentation at different loads and loading rates. • Good correlation between the wear rates and the ratio between the materials' hardness H and reduced moduli E*0.447. • The H/E*0.447 ratio is proposed as a new means to rank the wear resistance of materials in boundary lubricated contacts. [ABSTRACT FROM AUTHOR]