Tribological Potential Research Articles

Zwitterionic Poly-Carboxybetaine Polymers Restore Lubrication of Inflamed Articular Cartilage.

Osteoarthritis is a degenerative joint disease that is associated with decreased synovial fluid viscosity and increased cartilage friction. Though viscosupplements are available for decades, their clinical efficacy is limited and there is ample need for more effective joint lubricants. This study first evaluates the tribological and biochemical properties of bovine articular cartilage explants after stimulation with the inflammatory cytokine interleukin-1β. This model is then used to investigate the tribological potential of carboxybetaine (CBAA)-based zwitterionic polymers of linear and bottlebrush architecture. Due to their affinity for cartilage tissue, these polymers form a highly hydrated surface layer that decreases friction under high load in the boundary lubrication regime. For linear pCBAA, these benefits are retained over several weeks and the relaxation time of cartilage explants under compression is furthermore decreased, thereby potentially boosting the weeping lubrication mechanism. Bottlebrush bb-pCBAA shows smaller benefits under boundary lubrication but is more viscous than linear pCBAA, therefore providing better lubrication under low load in the fluid-film regime and enabling a longer residence time to bind to the cartilage surface. Showing how CBAA-based polymers restore the lost lubrication mechanisms during inflammation can inspire the next steps toward more effective joint lubricants in the future.

Hydrophobic and Tribological Properties of Biomimetic Interfaces

Bionic interfaces have received much attention owing to their attractive hydrophobic and tribological potential. Although a great deal of research has been carried out on biomimetic nanostructures, the basic theory, experimental application, and related techniques of hydrophobicity of biomimetic nanostructures, as well as the relationship between the state of lubricants and friction in tribology have not been fully explored. In this review, based on a brief discussion of the theory of hydrophobicity, the role of two-dimensional bionic structures in the wet state is introduced, and the wetting mechanism and applications are discussed. Then, the synergistic effects and mechanisms of bionic weaving and lubricants in the dry/wet friction state are investigated. In addition, the contribution of bionic structures to the fields of hydrophobicity and tribology further deepens the knowledge and enriches the practical applications of bionic surface weaving.

Solid lubrication performance of multi-layered V2CTx coatings

MXenes induce excellent wear resistance under solid lubrication due to their distinctive surface chemistry, easy-to-shear ability, and capability to form low-friction and wear-resistant tribofilms. However, beyond the extensively studied Ti3C2Tx, other promising members of the MXene family remain largely underexplored. Therefore, we spray-coated multi-layer vanadium carbide (V2CTx) coatings (thickness ∼10.8 μm) on steel substrates and studied their tribological performance for prolonged times (10,000 cycles) using a reciprocating ball-on-disk tribometer with acting contact pressure of 445 MPa in ambient conditions. Results show that V2CTx-coated substrates demonstrate an 8-fold reduction in friction (COF of 0.11) and a 10-fold wear rate reduction (1.405 × 10−6 mm3 N−1 m−1). High-resolution materials characterization confirmed that the remarkable tribological performance of these coatings can be traced back to the formation of protective films on the substrate (tribofilm) and counterbody (transferfilm) consisting of contact pressure and frictional heat-induced degraded, deformed, exfoliated V2CTx nanosheets, nanocrystalline oxides, and amorphous carbon debris. This work fully elucidates the tribological potential of V2CTx, which is of utmost relevance for designing high-performance lubricating materials. Our work has assessed the performance of multi-layer V2CTx (M2XTx) due to its remarkable thermal stability, low molecular weight, good mechanical properties, and high interlayer spacing, thus serving as an entry point into diverse MXene compositions, including M4X3Tx (V4C3Tx).

The effect of temperature on the transfer layer of an aluminium alloy on tool steel and the effect of CrN coating

It is essential to explore temperature's crucial role while unveiling the intricacies of tribological interplay in CrN-coated steel-alloy systems. In the present study, tribological potential of CrN-coated hot-work tool steel was investigated under unidirectional single-pass sliding wear conditions. The sliding wear tests were performed at different temperatures (i.e., 20 °C, 100 °C, 200 °C, 300 °C, 400 °C and 500 °C) for the different sliding distances between 2 mm and 68 mm to explore the effect of temperature on the initiation and evolution of the transfer of an aluminium alloy (EN AW-6060). The effect was studied in terms of the contact area of the aluminium alloy and the volume transferred to the surface of the CrN. In addition, the structure of the wear trace and the equivalent friction coefficient were monitored with respect to the sliding distance and the temperature. The results show the strong dependency of the tribological potential of the CrN coating and the aluminium alloy on the temperature but show insignificant dependency on the sliding distance. When sliding up to 200 °C, the transfer was found to be dependent on the surface roughness of the coating, while strong adhesion led to the aluminium alloy's transfer during sliding at higher temperatures, that is, above 300 °C. At 500 °C, the CrN coating formed a self-protective Cr2O3 oxide that reduced the adhesive transfer of the alloy to the CrN compared to that at 200 °C–300 °C.

Experimental Wear Analysis of Nano-Sized Titania Particles as Additives in Automotive Lubricants

This study focuses on the wear effects of nano-sized titania as a potential engine lubricant additive. Titanium dioxide nanoparticles have promising wear-reducing properties and significant tribological potential. In this article, titania nanoparticles were homogenized in Group III automotive oil at five different concentrations (0.1; 0.2 … 0.5 wt%). The nanodoped oil samples were tested on a linear oscillating tribometer with oil circulation. Based on the tribological results, titania nanoparticles increased friction by 20–32% but can reduce the wear area by up to 32%. According to the confocal microscopic examination, wear volume can be reduced by up to 57% with titania nanoparticles. Titania nanoparticles improved the repeatability of tribological measurements. A scanning electron microscopy examination of the wear track revealed that the characteristic wear of the tribological system was abrasive, but a significant amount of adhesive wear was also observed. Energy dispersive X-ray spectroscopy analysis found that the nanoparticles fill the deeper trenches of the wear. The worn surface uniformly contains TiO2 particles and the quantified normalized titanium concentration was between 0.56 and 0.62%.

Surface Modification of Silica Nanoparticles with Ethyl Oleate for the Purpose of Stabilizing Nanolubricants Used for Tribological Tests

Long-term sustainability and decreasing amount of fossil oil reserves require a partial or complete transformation of traditional lubricating oils. The use of silica nanoparticles as a lubricant additive has a huge tribological potential, which has already been discussed in numerous articles. Nanosized silica shows excellent results in reducing friction and preventing wear, but they quickly aggregate and settle after homogenization in oils. For long-term stable dispersion of lubricating oils containing nanoceramics, the surface of the particles was modified with ethyl oleate. The surface modification, the ethyl oleate applied to the surface of the nanosilica, was confirmed by Fourier-transform infrared spectroscopy. Group III based lubricating oil was prepared using the surface-modified nanosilica. The particle size of the nanoparticles in the lubricating oil dispersion was examined by dynamic light scattering. Oscillating tribometer measurements were performed with different concentrations (0.1; 0.2; 0.3 wt%) of nanolubricants. Based on the tribological results, the friction coefficient of the surface-modified nanosilica is more stable, its wear is 15% lower compared to the reference. There is no significant change in the magnitude of the friction coefficient. It can be concluded that the ethyl oleate surface modification method may be suitable for tribological investigations of the acting mechanisms of nanoparticles.

In-Situ Formation of MoS2 and WS2 Tribofilms by the Synergy Between Transition Metal Oxide Nanoparticles and Sulphur-Containing Oil Additives

This works investigates the in-situ formation of MoS2 and WS2 tribofilms by the synergy between transition metal oxide nanoparticles and conventional sulphur-containing anti-wear and extreme pressure additives. The formation of these low friction tribofilms can be obtained under reciprocating sliding contact and under extreme pressure conditions, as evidenced using X-ray photoelectron spectroscopy. Under reciprocating sliding conditions, the synergy between transition metal oxide nanoparticles and the ZDDP leads to coefficients of friction around 0.06 before they rise as consequence of oxidation. The synergy is more outstanding in extreme pressure conditions, particularly for MoO3 nanotubes combined with extreme pressure additive. This combination outperforms base oil mixtures containing EP additive or MoS2 nanotubes. While MoS2 nanotubes build superb extreme pressure tribofilms containing iron and molybdenum oxides and sulphides, MoO3 nanotubes are able to build similar tribofilms that can continuously re-sulphurize in the presence of the extreme pressure additive. Despite having a similar chemistry, MoO3 nanotubes are observed to sulphurize more easily when compared to WO3 nanoparticles. The work highlights the tribological potential of these nanoparticles otherwise typically used as precursors for the synthesis of transition metal dichalcogenide nanoparticles.

Investigation on the lubrication potential of graphene oxide aqueous dispersion for self-mated stainless steel tribo-pair

Due to high concerns for environmental protection and resource conservation, water-based lubrication with some additives is gaining the attention of researchers. Hence, the present study has been conducted to explore the tribological potential of lubricant containing graphene oxide (GO) as an additive in water. The friction and wear performance was evaluated for self-mated SS 304 under reciprocating sliding using a ball-on-disc configuration under high contact stress (∼1.42 GPa or higher). The results indicate that 0.1 wt% is the optimum content of graphene oxide under the conditions used in the study and has the capability to reduce friction coefficient from 0.56 (pure water) to 0.12 with an attendant reduction in wear volume by 68%. The enhancement in tribological performance has been attributed to the formation of a low shear strength tribo-layer of graphene on the surface of both the ball and the disc. The effect of normal load and sliding speed for optimized concentration was also investigated. The average coefficient of friction was observed to increase with load whereas, it was observed to decrease with increase in speed till 0.05 m/s beyond which it increased.

The tribological potential of graphene growth from solid waste

This study aimed to identify the tribological potential of graphene growth from solid waste products on copper substrate via the chemical vapour deposition method. The study focused on graphene growth from fruit cover plastic waste (FCPW) and oil palm fibre (OPF), the graphene structure was examined using Raman spectroscopy. Then, the tribological testing was performed using a ball-on-disc tribometer, and the hardness was performed using a nano-indenter on both the worn and unworn surfaces. The results show that graphene was successfully grown from both sources. Meanwhile, the tribological study found that both coatings showed a higher coefficient of friction (μ) compared to pure copper. However, the wear rate (k) was contradicted by the μ where the k was found to be 60% to 75% lower than pure copper. Finally, the hardness analysis revealed that the coating was damaged at 100 m sliding as the surface hardness increased.

The tribological potential of graphene growth from solid waste

This study aimed to identify the tribological potential of graphene growth from solid waste products on copper substrate via the chemical vapour deposition method. The study focused on graphene growth from fruit cover plastic waste (FCPW) and oil palm fibre (OPF), the graphene structure was examined using Raman spectroscopy. Then, the tribological testing was performed using a ball-on-disc tribometer, and the hardness was performed using a nano-indenter on both the worn and unworn surfaces. The results show that graphene was successfully grown from both sources. Meanwhile, the tribological study found that both coatings showed a higher coefficient of friction (μ) compared to pure copper. However, the wear rate (k) was contradicted by the μ where the k was found to be 60% to 75% lower than pure copper. Finally, the hardness analysis revealed that the coating was damaged at 100 m sliding as the surface hardness increased.

Self-lubricating Ti3C2 nanosheets/copper composite coatings

While MXenes have been strongly studied in the possible applications including energy storage, electromagnetic interference shielding, photo-, electro- and chemical catalysis, its tribological potential as a lubricant remains relatively unexplored. Here, few layer Ti3C2 nanosheets/copper composite coatings are designed and synthesized by a facile electrodeposition technique at room temperature. Their tribological behaviors are studied under dry sliding. Post-test observations including morphology and composition analysis on the wear tracks along with counterpart are conducted to understand their friction and wear mechanisms. The results show that Ti3C2 nanosheets/copper composite coatings exhibit lower of friction and wear rate than their Ti3C2-free counterparts. Our results firstly demonstrate the feasibility of using MXenes as lubricating nanofillers to significantly improve tribological properties of metal matrix composites.

Determination of the Mechanism of Tribocorrosion of D16T Alloy According to the Electrode Potential

We study the influence of the contact speed of friction surfaces on the tribocorrosion behavior of D16Т alloy in acid rain. It is shown that the electrode potential, the friction coefficient, and the loss of material in the course of tribocorrosion qualitatively are well correlate and depend on the velocity of mutual displacement of the surfaces of friction couples. It is demonstrated that the activation potential, corrosion potential, and tribological potential enable one to estimate the fracture mechanism of materials passivated in corrosive media.

Wear characteristics of recycled carbon fibre-filled polypropylene composites via acidic surface treatment

Recycling and reuse of waste carbon fibre for making value-added products is a wise disposal management. This research is focusing on the tribological potential of nitric acid treated recycled carbon fibres (rCFs) as reinforcement in polypropylene (PP). The coefficients of friction and wear rate of this composite at different fibre loadings of 0.5, 1, 3, 5 and 7 wt% were determined for the effect of acid treatment. Composites with acid treated rCF showed smaller COF (0.30-0.33) than those with untreated rCF (0.51-0.55). In contrast, wear rate was higher for the composites filled with treated rCF than those with untreated rCF. The increment of fibre loading from 5 wt% to 7 wt% decreased the wear rate for both untreated and acid treated composites owing the formation of stable patch film and transfer film. The films effectively prevented direct contact of the composites with the counterface; hence, wear was greatly inhibited.

Effect of graphene addition and tribological performance of Al 6061/graphene flake composite

Graphene, no wonder has attracted a significant research interest due to its extensive physical properties at its single atomic thickness and 2D morphology. The current studies focus on the role of graphene in reducing the wear and frictional coefficient of Al 6061–graphene-reinforced metal–matrix composites (MMC’s). Reinforcement chosen is 0.3, 0.6 and 0.9 wt% of graphene to investigate the self-lubricating property under dry wear condition and processed through the ultrasonic liquid processor. The dry frictional wear test was carried out using pin-on-disc tribometer to evaluate the effect of graphene content in the composites under various normal load (5, 10, 15 N) and disc sliding speed (0.4, 0.8, 1.2 m/s) conditions. The results show that there is a significant increase in the hardness and wear resistance and a reduction in the coefficient of friction (μ) values compared to pure alloys. Arithmetic mean surface roughness values (Ra), max profile peak (Rp) and max valley depth (Rv) are found to be comparatively lower than the pure alloy. Due to the tribological potential coupled with improved strength and surface roughness values, Al 6061–graphene composite are excellent candidates for all applications where it is subjected to Friction and wear.

Assessment of Mechanical and Tribological Properties of Al 2024- SiC - Graphene Hybrid Composites

In the recent years, enormous research has been carried out and reported on ceramic and carbon based reinforcement. Graphene, no wonder has attracted significant research interest due to its extensive physical properties at its single atomic thickness and 2-D morphology. The current studies focus on the role of Graphene in reducing the wear and frictional coefficient of Al 2024- SiC - Graphene reinforced hybrid composites. Reinforcement chosen is 4, 8 and 12wt. % of SiC with 0.5wt. % of Graphene to investigate the lubricating property under dry wear conditions and processed through the ultrasonication and ball milling. The processed mixtures are hot compacted and microwave sintered. Hardness, density, X-ray diffraction and flexural strength analysis were done on developed composites. The dry frictional wear test were carried out using pin-on-disc tribometer to evaluate the effect of Graphene and SiC content in the composite under various normal load and disc speed conditions. Further, wear resistance and a reduction in the coefficient of friction (μ) values compared to pure alloys were observed. Surface roughness values (Ra) and microscopic studies on wear tracks were carried out. The possible tribological potential coupled with improved mechanical properties and surface roughness of Al 2024- SiC - Graphene hybrid composite processed through powder metallurgy were discussed.

Influence of the heat treatment path on the martensite phase and dry reciprocating wear behavior of dual-phase steels

In order to explore the tribological potential of dual-phase (DP) steel as a wear-resistant material, the wear and friction characteristics of this steel, which consists of soft ferrite and hard martensite phases, was investigated. A low-carbon (0.11% C) steel was subjected to three different annealing heat treatments in order to develop different martensite percentages and morphologies, i.e., island types, a bulky and interconnected network, and fibrous (fine, needle-like), respectively. Dry reciprocating wear tests were performed under atmospheric conditions of 25 °C using a pin-on-disk apparatus at different loading conditions ranging from 18.9 N to 43.6 N and at a constant sliding velocity of 0.22 m/s. The lowest wear rate was obtained for the DP steel with an ~87% volume fraction (V F ) of martensite, reflecting the effect of hardness imparted by the increasing amount of martensite, which is a hard and load-bearing phase, while the highest wear rate was for the DP steel with a ~36% martensite V F . The analysis of the surface, subsurface and wear debris of specimens using a scanning electron microscope (SEM) showed that the wear mechanism was mainly mild oxidative wear. The friction and wear rate of the steels are explained with respect to the microstructure and the wear mechanism.

The Stability of the Coefficient of Friction and Wear Behavior of C/C–SiC

To develop a fundamental understanding of the tribological behavior of carbon fiber-reinforced silicon carbide (C/C–SiC) composites as brake pads and discs for high-speed trains, we have studied the brake friction properties of C/C–SiC composites at initial braking speeds ranging from 30 to 63 m/s. The friction mating pairs were fabricated by two methods to obtain composites of different SiC content. The composite with a SiC content of 40.3 % was used as the friction pad, and that with a SiC content of 85.6 % was used as the friction disc. In our experiments, an interesting turning point of 59 m/s was observed: the coefficient of friction (COF) decreased from 0.43 to 0.32 with increases in the braking speed from 30 to 49 m/s, at which braking speed it reached a plateau; the wear rate displayed a cubic curve against initial braking speed and reached a minimum of 315 mm3/MJ at 59 m/s. The topographical observations by scanning electron microscope combined with the residual stress analysis revealed that the limited number tribochemical layers, as well as the mismatch of thermal expansion coefficient between the carbon fiber and matrix, contribute to the unusual tribological characteristics of C/C–SiC composites. The experimental results suggest the good tribological potential of self-mated C/C–SiC composites in high-speed working conditions in terms of a steady COF and low wear rate.

The Enhanced Tribological Properties of NiAl Intermetallics: Combined Lubrication of Multilayer Graphene and WS2

In recent years, reducing friction and wear-related adverse impacts on efficiency and durability in moving mechanical systems has gained increased attention. Herein, the search continues for novel materials and lubricants that can potentially reduce friction and wear. As one of the emerging self-lubricating materials, the tribological potential of graphene has been researched deeply. This article was dedicated to explore the combined lubrication of multilayer graphene (MLG) and WS2. The as-prepared sample of NiAl–1.5 wt% MLG–5 wt% WS2 (NB) exhibited excellent tribological properties. During the sliding process, a continuous lubricating film was formed to provide the low-strength junctions at the interface, reducing the friction coefficient and wear rate. Moreover, the MLG played the role of reinforcement particles and improved loading carrying ability.

Extraordinary Macroscale Wear Resistance of One Atom Thick Graphene Layer

During the last few years, graphene's unusual friction and wear properties have been demonstrated at nano to micro scales but its industrial tribological potential has not been fully realized. The macroscopic wear resistance of one atom thick graphene coating is reported by subjecting it to pin‐on‐disc type wear testing against most commonly used steel against steel tribo‐pair. It is shown that when tested in hydrogen, a single layer of graphene on steel can last for 6400 sliding cycles, while few‐layer graphene (3–4 layers) lasts for 47 000 cycles. Furthermore, these graphene layers are shown to completely cease wear despite the severe sliding conditions including high contact pressures (≈0.5 GPa) observed typically in macroscale wear tests. The computational simulations show that the extraordinary wear performance originates from hydrogen passivation of the dangling bonds in a ruptured graphene, leading to significant stability and longer lifetime of the graphene protection layer. Also, the electronic properties of these graphene sheets are theoretically evaluated and the improved wear resistance is demonstrated to preserve the electronic properties of graphene and to have significant potential for flexible electronics. The findings demonstrate that tuning the atomistic scale chemical interactions holds the promise of realizing extraordinary tribological properties of monolayer graphene coatings.

ZnAlMg Hot-Dip Galvanised Steel Sheets – Tribology and Tool Wear

For the last few years zinc magnesium alloys on cold rolled steel have been investigated in detail because of their potential to provide better corrosion protection than pure zinc coatings. However, for the introduction into the automotive industry it is also necessary to learn more about their tribological behavior. In this paper the tribological potential of ZnAlMg hot dip galvanized steel sheets (HDG/ZM) was studied in terms of sliding properties, adhesive and abrasive tool wear and compared to hot dip galvanized reference material (HDG/Z). Different tribological tests were performed. The friction coefficient was determined directly by strip draw tests at constant contact pressure. The deep drawing property was tested by forming model cups. Two different oils, a pure corrosion protection oil and a prelube were tested in each of the tribological tests. Abrasive tool wear was studied according to the SEP1160 standard. Adhesive tool wear (galling) was characterized on different tool material and compared to the results for hot dip galvanized reference material. HDG/ZM strips showed improved friction behavior in the strip draw test when compared to classical hot dip galvanized reference material. The abrasive tool wear is comparable to HDG/Z material, however, the galling was found to be less than for pure zinc, and the morphology of the coating material transferred to the tool during deep drawing is also different. This makes HDG//ZM an interesting system not only with respect to corrosion but also in terms of tribology, thus providing clear advantages in formability.