Tribology Letters最新文献

As hydrogen reduces the fatigue life of 100Cr6 bearing steel significantly, extensive research on the interaction of hydrogen with 100Cr6 is necessary. This study investigated the influence of rolling/sliding tribotesting performed on a micro-pitting-rig on the hydrogen absorption and trapping behaviour of 100Cr6 bearing steel. Thermal desorption mass spectrometry was used to compare the hydrogen desorption spectra of 100Cr6 samples after tribological tests and static heated oil-immersion tests to untested reference samples. The approach was chosen to further understand the influence of both microstructural deformation as well as steel-oil contact on the hydrogen absorption and trapping behaviour of 100Cr6. The tribological test showed a stable friction behaviour and mild wear which was dominated by local plastic deformation of surface asperities. Despite the mild wear, a change in de-trapping temperatures was found for tribotested samples compared to oil-immersed and untested reference samples. This finding indicates that even mild tribotesting conditions alter the hydrogen trapping behaviour of 100Cr6 bearing steel.

According to the comparative experiments on friction and wear of Al–TiC, Al–Bi (RC) and Al–Bi–TiC alloys, the friction-reduction and wear-resistance mechanisms of TiC/Bi were systematically investigated. The alloys were examined via the scanning electron microscope equipped with an energy dispersive spectrometer and a shape-measuring laser microscope (VK-X100). Basing the achievements, the Bi-phase accumulates on the friction surface with gradual enrichment, possessing anti-friction and self-lubrication on the friction surface. The stable TiC/Bi self-lubricating layer of Al–Bi–TiC alloy make the values of the wear measurements reduce from 82.2 mg to 26.7 mg in 2 h. Meanwhile, TiC particles have uniform load capacity and interfacial pinning properties, which solve the peeling off from the worn surface of Bi-phase.

This work indicates that the core–shell structure is expected to meet the requirements of high friction and low wear for clutches. In the article, two types of core–shell particles are added to Cu-based friction materials for tribological testing. The results showed that as the concentration increased, the coefficient of friction showed a trend of first increasing (from 0.13 to 0.67) and then decreasing (from 0.67 to 0.57). At the same concentration, the COF of carbon coated copper (Cu@C) friction material is 0.4 higher than that of copper coated carbon (C@Cu) friction material, but the wear rate is 43.1% lower. Both materials exhibit high COF but their wear behavior are different due to the distinct components of the friction film.

Bolted joints are widely used in various engineering structures. The bolted joint may become loosening under long-term oscillating load, and cause reciprocating friction between the contact interfaces. Acoustic emission (AE) is a phenomenon of rapid release of transient elastic waves, which will be generated continuously during the reciprocating friction. The friction conditions will affect the characteristics of the contact interface and the related AE signals. Therefore, analyzing the quantitative relationship between friction conditions and AE signal is significant for applying AE technique in bolt loosening monitoring. However, researches on the relationship between AE Vrms and friction operating parameters are mostly focused on rotating machineries currently, whether the obtained conclusions are suitable for bolted joints is not clear. This paper finds that the commonly used quantitative relationship between the AE Vrms and friction operating parameters is not suitable for bolted joint structures by comparing the theoretical and experimental AE Vrms. The relationship is then modified through exponential parameter fitting and verified using the same experiments in this paper. The results show that the modified equation can accurately describe the quantitative relationship between the AE Vrms and the friction operating parameters, thus revealing the mechanism of acoustic emission signals generated during the gross-slip.

In this paper, a Cu–C coating was prepared on a copper substrate through a magnetron sputtering coating process, and the effect of a composite grease containing WS₂ and MoS₂ on its tribological behavior and electrical conductivity was studied. Experimental results revealed that the Cu–C coating exhibited certain friction-reducing effects under dry sliding conditions with a 5 N load. In the lubricated state with polyurea-based grease, the Cu–C coating demonstrated lower friction coefficients and contact resistances at 2 N and 5 N loads, accompanied by reduced wear rates, indicating a synergistic effect between the lubricant and the coating, enhancing the friction-reducing performance. Furthermore, the incorporation of additives such as WS₂ and MoS₂ can effectively decrease both friction and contact resistance. Notably, 1% WS₂ grease, in combination with Cu–C coating, exhibits superior compatibility, resulting in optimized tribological properties and electrical conductivity. Therefore, the results of this study suggest that the combination of Cu–C coatings with WS₂ grease can effectively improve the electrical conductivity and friction-reducing and anti-wear capabilities of Cu–Cu sliding pairs, providing an effective solution for enhancing the electrical conductivity of electric vehicle connectors and improving the overall efficiency of the battery system.

The environmental temperature alters the frictional behaviour by changing the state of the current-carrying contact interface, which makes the electrical contact invalid. In this work, the effects of three different temperatures (− 20, 0, 20 °C) on the current-carrying tribological behaviour of C–Cu tribo-pairs in high humidity environment (85%) were discussed. The evolution laws of friction coefficient, wear volume, contact surface properties, and contact resistance of tribo-pairs were studied, and the current-carrying wear mechanism of C–Cu at low temperature was analyzed in depth. The variation of friction coefficient with temperature shows a similar rule before and after current-carrying, that is, regardless of the current, the friction coefficient increases as temperature falls. However, the average friction coefficient at each temperature is lower than that without current. Although it will hasten the material surface's oxidation, a drop in temperature will effectively lessen the transfer behaviour of copper to carbon surface and reduce the wear volume of carbon materials. The amount of copper transferred increases as current rises. Compared with current, the change of temperature has a greater impact on the damage of tribo-pairs. At room temperature, the contact resistance under high current is greater than that of low current. However, the rule is just the opposite under low temperature (0 and − 20 °C). In addition, at 0 °C, although the contact resistance of low current (5 A) decreases significantly in the early stage of friction, its average resistance and fluctuation amplitude are the largest. As the temperature decreases, the current-carrying wear mechanism of C–Cu contact pairs gradually changes from adhesive wear to fatigue wear.

Reduction of friction and wear by lubrication is necessary to improve the efficiency and prolong the lifespan of industrial machinery. However, several aspects regarding the lubrication effects in additive-combined oil are still unresolved. This study focuses on the effects of combining zinc dialkyldithiophosphate (ZnDTP), molybdenum dithiocarbamate (MoDTC), and Ca sulfonate on the frictional behavior of poly-α-olefin 4 (PAO4) lubricant oils. Ball-on-disk friction tests demonstrated that the exclusive addition of high-base Ca sulfonate solution reduced friction and wear of the lubricating oil. When combined with ZnDTP and MoDTC, the friction coefficients of PAO with high-base and low-base Ca sulfonate are affected by competitive reactions on the sliding surface. Quartz crystal microbalance with dissipation monitoring measurements suggests that high-base Ca sulfonate forms a stronger adsorption film than low-base Ca sulfonate. Atomic force microscope observations confirmed that the addition of low-base Ca sulfonate reduced friction and wear, whereas high-base Ca sulfonate induced competitive reactions with ZnDTP and MoDTC. This study provides valuable insights into the effects of the combination of additives on the lubricity of PAO and their impact on friction and wear characteristics, which are valuable for the design of suitable lubricants for industrial machinery.

Reducing friction using lubricant is of great significance to reducing energy consumption and extending the life of machinery. Surface texturing is effective to enhance the lubrication condition, and it is crucial to properly design the texture’s morphology. In this study, a sector-shaped surface texture is designed and demonstrated using both numerical and experimental methods. A computational fluid dynamic method based on Navier–Stokes equations and a two-phase cavitation model is performed to evaluate the effect of the texture in the hydrodynamic lift and to optimize the geometrical parameters of the texture. The mechanism associated with the additional hydrodynamic pressure generation is also revealed according to the results of the simulation. Then, pin-on-disk rotary friction experiments are performed on steel disks textured by a femtosecond laser to verify the lubricant effect of the proposed texture. The results of the experiment suggest that the sector-shaped textures reduce friction more than conventional circle-shaped textures, which coincides well with the results of the simulation.

The current investigation delved into the friction and wear characteristics of abrasive-finished Inconel 718 alloys fabricated by additive manufacturing and casting methods. Silicon carbide balls were used as counter-body materials for all tribology tests. Variable loads of 10 N, 20 N, and 30 N were applied, along with frequencies of 5 Hz and 15 Hz, while maintaining a 1 mm stroke length for 30 min. Cast samples showed an increase in coefficient of friction (COF) when the load increased from 10 to 20 N at 5 Hz. COF value was decreased from 0.28 to 0.25 when the load was increased from 20 to 30 N while the frequency was maintained at 5 Hz. At the same frequency of 5 Hz, additively manufactured samples displayed a constant increase in COF from 0.19 to 0.35 as the load increased from 10 to 30 N. Consistent COF values were determined at 15 Hz for cast and additively manufactured samples. The COF for cast samples at a frequency of 15 Hz was 0.26, 0.25, and 0.25 for loads of 10 N, 20 N, and 30 N, respectively. For the same loads and frequencies, COF values of 0.23, 0.24, and 0.24 were reported in additively manufactured samples. At 15 Hz, both cast (7.25 × 10^–6 mm³/N.m to 9.91 × 10^–6 mm³/N.m) and additively manufactured (5.80 × 10^–6 mm³/N.m to 6.18 × 10^–6 mm³/N.m) samples exhibited constant increasing trends of specific wear rates when the loads increased from 10 to 30 N.

Graphical Abstract