Tribology Letters最新文献

Aminoguanidine-based ionic liquid which can reduce the friction coefficient and wear depth has been developed as lubricant additives for the piston ring and cylinder liner within 80–240 °C. The friction coefficient and wear depth reduction become more significant as the temperature increases. At 240 °C, the coefficient of friction decreases by 23.1% compared to fully formulated mineral based engine oil (FFO). The wear depth of the piston ring and cylinder liner decreases by 9.1% and 16.0%, respectively. Addition of aminoguanidine-based ionic liquid (AO-IL) promotes the tribo-chemical reaction of zinc dialkylphosphorodithiloate (ZDDP), distributing S, P and Zn on the cylinder liner honing platform rather than in the honing groove. The plastic deformation causes a significant reduction of flakes on the edges of the cylinder liner honing platforms and less furrow damage along the sliding direction. The worn surface of the diamond-like carbon (DLC) piston ring shows a denser distribution of white bright spots and a higher sp²C=C/sp³C–C ratio.

Modeling mild wear damage mechanisms, such as oxidative wear, is highly complex due to the many mechanical and chemical actors involved. To clarify these mechanisms, the temperature-activated diffusion of oxides through exposed surfaces is used. Results indicate that diffusion kinematics are higher than those determined for the same temperatures without fretting phenomena, an effect that is especially visible when the slip speed is low (< 1 m/s). To understand the mechanism of this damage, the present study examined the evolution of the contact temperature and the dissipated heat, considering temporal non-linearities and roughness effects. This is accomplished by analyzing a case study of an axial bearing in which radial fretting is experimentally induced after applying a variable normal load and by comparing the experimental results to the theoretical calculations in the thermal-activated diffusion model.

This paper describes how research over the last 20 years has advanced our understanding of the mechanisms of action of ZDDP, especially with respect to tribofilm formation. We now know that ZDDP tribofilm formation is promoted by applied shear stress and this explains many of the features of these films. We also now recognise that ZDDP tribofilms evolve during rubbing from relatively soft, long chain polyphosphate films to much more wear-resistant, short chain phosphates. Several disadvantages of ZDDPs as lubricant additives have emerged in recent years, in particular their tendency to increase friction in thin film rubbing conditions, their promotion of micropitting wear, and accelerated wear when present together with soot contaminants in engine oils. Research has revealed the origins of all these effects. Over the last 20 years there have been growing efforts to model ZDDP tribofilm formation, both at a macro- and molecular-scale, so far with limited success. Finally, this paper outlines some aspects of ZDDP behaviour that we still do not fully understand and where further research is needed.

Graphical Abstract

Scuffing, a type of wear found in highly stressed or poorly lubricated contacts, is characterized by a rapid increase in friction and severe plastic deformation of the near-surface material. Scuffing has proven difficult to study because it initiates unpredictably, progresses rapidly, and typically develops within an inaccessible contact interface. Although there have been successful in-situ studies of scuffing in real-time, the transparent counter body needed for these studies changes the interactions between the surfaces and the lubricant, which affects the scuffing process in unknown ways. This paper describes the development of X-ray-compatible tribometry to study the scuffing of self-mated steels in-situ and in real-time. The method uses a crossed cylinders configuration with a thin (500 μm thick) stationary component and a small (≈200 μm) contact width to maximize X-ray interactions with atoms within the stress field generated by the contact. The resulting instrument and method are used to benchmark the scuffing response of self-mated 52,100 steel under tribologically challenging ‘oil-off’ lubrication conditions. The results demonstrate reliable scuffing in this configuration despite the relatively small contact areas and loads used. Following scuffing, gross plastic deformation was observed on both surfaces along with significant subsurface grain refinement and flow only on the stationary surface, which experienced constant contact. Interestingly, high friction initiated at specific locations of the migratory surface, which experienced intermittent contact, and then propagated across the track over time, suggesting that local conditions of the migratory surface dominated friction leading into the failure event.

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This study investigates the influence of the crystallinity of MoS₂ nanoparticles on their tribological performance, when used as lubricant additives in presence of a succinimide-based dispersant. Friction tests were conducted at room temperature and 100 °C. Characterization techniques, such as TEM, XPS, TGA, and DLS were used to analyze the structural and chemical properties of the nanoparticles and the tribofilms formed during the friction tests. At room temperature, low crystallinity nanoparticles show superior friction reduction due to their structural defects which facilitate their exfoliation and make easier dispersant adsorption and effective nanoparticle interaction with surfaces. Higher friction coefficients are obtained with the high crystallinity nanoparticles. This is attributed to a less easy exfoliation of the nanoparticles together with greater difficulty for the dispersant to interact with closed-structure nanoparticles. The tribofilm is thicker with high crystallinity particles and made of exfoliated MoS₂ sheets together with intact nanoparticles. At 100 °C, the friction performance of both nanoparticles are similar and very good as the dispersant looks to desorb from the rubbing surfaces, highlighting the significant impact of temperature on dispersant behavior and friction reduction. These findings underline the importance of tailoring lubricant formulations to both the crystallinity of MoS₂ nanoparticles and the operating conditions in order to optimize tribological performance.

A self-developed tube-to-tube contact fretting wear tester was used to conduct fretting wear tests on Zr-4 fuel rods in pressurized water reactors of nuclear power plants under three fretting wear modes (tangential, radial, and dual-motion fretting) with different normal loads [F_n = 15–25 (20), 30–50 (40), and 45–75 (60) N]. The test results show that the normal load and fretting wear mode have a significant effect on the fretting wear behaviors of Zr-4 alloy tube. Comparing the different fretting wear modes, the contact surface is almost coordinated by elastic deformation under the radial fretting wear mode, with the slightest damage; for tangential fretting wear mode, the damage mechanism is mainly fatigue wear and delamination; the most severe damage was observed under the dual-motion fretting wear mode, where the wear mechanism consisted of a combination of delamination, abrasive wear, adhesive wear, and oxidative wear.

For the abrasive wear of hard/soft dynamic seals, simplified uniform hardness research have been difficult to support the technology development at this stage. Therefore, the tribological behavior of non-uniform hardness particles was investigated. The results showed that the particles breakage and non-uniform effect combined to influence wear level. This caused the damage to the interfaces by the particles not to be the result of an average of both the hardness. For a clearer explanation, the influence of non-uniform hardness effect was discussed through a combination of the model and the phenomenon. The significance of this work was to enrich the existing understanding of the hardness effect and thus to provide suggestions for improving the wear resistance of hard/soft dynamic seals.

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Friction-induced stick–slip vibrations (FISSV) commonly occur in mechanical systems, posing risks to equipment like high-speed train brakes, causing instability, and threatening safety. To address this, we propose using textured surfaces of friction pairs to suppress FISSV. Through simulations on a friction testing machine, we explored the impact of surface texturing on FISSV. The results indicate that surface texturing significantly influences interfacial wear debris flow and contact characteristics, thereby regulating FISSV behavior. Textured surfaces better collect and store debris, reducing its involvement in friction and forming larger contact platform of metal substrate. This increases interface contact stiffness, preventing FISSV. A combination of macro-grooves and microtextures was particularly effective. Thus, appropriate surface texturing design can enhance system stability and reliability by effectively suppressing FISSV.

Macrotextured silicone breast implants are associated with several complications, ranging from seromas and hematomas to the formation of a rare type of lymphoma, known as breast implant-associated anaplastic large cell lymphoma (BIA-ALCL). The presence of silicone wear debris has been detected within the peri-implant region and fibrotic capsule and histological analyses reveal inflammatory cells surrounding debris particles. However, it is unclear how these debris particles are generated and released from macrotextured implant surfaces, and whether wear debris generation is related to implant stiffness. In this study, we created an accelerated implant aging model to investigate the formation of silicone wear debris produced from self-mated (“shell-shell”) tribological interactions. We created implant-like silicone elastomers from polydimethylsiloxane (PDMS) using Sylgard 184 base:curing agent (10:1, 12:1, and 16:1) and quantified their mechanical properties (E* = 1141 ± 472, 336 ± 20, and 167 ± 53 kPa, respectively). We created macrotextured PDMS samples using the lost-salt technique and compared their self-mated friction coefficient (< µ > = 4.8 ± 3.2, 4.9 ± 1.8, and 6.0 ± 2.3, respectively) and frictional shear stress (τ = 3.1 ± 1.3, 3.2 ± 1.7, and 2.4 ± 1.4 MPa, respectively) to those of the recalled Allergan Biocell macrotextured implant shell (E* = 299 ± 8 kPa, < µ > = 2.2, and τ = 0.8 ± 0.1). Friction coefficient and frictional shear stress were largely insensitive to variations in elastic modulus for macrotextured PDMS samples and recalled implant shells. The stiffest 10:1 PDMS macrotextured sample and the recalled implant shell both generated similar area fractions of silicone wear debris. However, the recalled implant shell released far more particles (> 10×), mainly within the range of 5 to 20 µm² in area. Bone marrow-derived macrophages (BMDMs) were treated with several concentrations of tribologically generated silicone wear debris. We observed widespread phagocytosis of wear debris particles and increasing secretion of inflammatory cytokines with increasing concentration of wear debris particles. Our investigation highlights the importance of avoiding macrotextured surfaces and mitigating wear debris generation from silicone implants to reduce chronic inflammation.

Investigating the relationship between the frictional performance and dynamic behavior of fullerenes under extreme conditions is crucial for the better development of fullerene-based lubricating materials. In this study, molecular dynamics simulations were used to investigate the boundary lubrication behavior of fullerenes confined between two carburized iron surfaces. Our findings demonstrate that the interlayer friction coefficient decreases exponentially with increasing applied load, increases with higher shear rates, and decreases with rising temperatures. The exponential decrease allows fullerenes to achieve ultra-low friction under high pressure, primarily due to their strong resistance to compressive deformation and the “ball-bearing effect”. Furthermore, as the applied pressure increases, the confinement becomes more pronounced, further accelerating the transition from sliding to rolling friction, thereby enhancing lubrication performance. This study deepens the understanding of the boundary lubrication mechanisms of fullerenes at carburized iron interfaces, offering valuable guidance for their application in advanced lubrication systems under extreme working conditions.

Graphical Abstract