Tribological Components Research Articles

Recent Advances in Tribology: A Review

In the last decade, there has been immense growth in research activities related to tribology. Tribology can have a big impact on the needs of industries to reduce losses and waste by developing new tribological components and materials. Hence, there is a strong connection between tribology and the fourth industrial revolution, i.e., industry 4.0. Tribology is a multidisciplinary field, and the results of research in the field of tribology are widely spread among various disciplines. This review paper briefs the recent advances in various research areas in tribology covering surface engineering, wear and lubrication. The main objective of this review is to summarize the new aspects in the field of tribology, like the numerical techniques of lubrication to model new lubrication schemes, solid superlubricity, superlubricity at the microscopic scale, superlubricity with coating and new 2D materials. The direction for future research in the field has been highlighted. The paper will be beneficial for researchers working in the field of tribology.

Advancing Surface Engineering for Tribology: From Functionality to Connectivity

Surface functionality plays a pivotal role in Tribology, a discipline dedicated to examining the interactions of surfaces in relative motion. The approach, known as Tribotronics, combines Tribology and electronics, enabling active tribological components to be embedded in larger systems and networks constituting the Industrial Internet of Things. Leveraging novel technologies such as advanced sensing coatings and triboelectric nanogenerators, the sensing capability of Tribotronic systems undergoes a transformative shift from a device‐centric to a surface‐centric paradigm. This critical advancement unlocks the potential for direct interface probing and in‐situ measurement of tribological processes, marking a significant milestone in the field. This emerging trend introduces the concept of the Internet of Surfaces, a novel perspective within surface engineering. It entails the amalgamation of sensing capabilities, embedded power generation, and external analytics, creating dynamic materials in the context of Industry 4.0.

Effect of Hydrogen Pressure on the Fretting Behavior of Rubber Materials

Safety and reliability are the major challenges to face for the development and acceptance of hydrogen technology. It is therefore crucial to deeply study material compatibility, in particular for tribological components that are directly in contact with hydrogen. Some of the most critical parts are sealing materials that need increased safety requirements. In this study, the fretting behavior of several elastomer materials were evaluated against 316L stainless steel in an air and hydrogen environment up to 10 MPa. Several grades of cross-linked hydrogenated acrylonitrile butadiene (HNBR), acrylonitrile butadiene (NBR) and ethylene propylene diene monomer rubbers (EPDM) were investigated. Furthermore, aging experiments were conducted for 7 days under static conditions in 100 MPa of hydrogen followed by rapid gas decompression. Fretting tests revealed that the wear of these compounds is significantly affected by the hydrogen environment compared to air, especially with NBR grades. After the aging experiment, the friction response of the HNBR grades is characterized by increased adhesion due to elastic deformation, leading to partial slip.

Emergence of Coated Piston Ring Scuffing Behavior on an Application-Oriented Tribological Model Test System

A major problem in lubricated piston ring/cylinder liner contact sliding systems is the tribological failure mechanisms known as scuffing. In order to evaluate and better understand this damage phenomenon in these tribological systems, a tilted linear tribometer (TE77) for application-oriented reciprocating model tests was developed and validated with scuffed field engine parts. With precise oil lubrication, original engine parts, such as CKS-coated piston rings (chromium-based coating with included aluminum oxides), original liners and fully formulated lubrications, were tested under conditions similar to the most critical part of the internal combustion engines (ICEs), known as fired top dead center (FTDC). Various in situ measurements during the tests allowed for a detailed investigation of the damage processes (crack transformation) on the tribological components. For the coated piston ring, vertical cracks were attributed to residual stresses, while horizontal cracks resulted from shear stresses. The crack transformation and wear results from other studies were confirmed for the liner. The results from FIB (Focused Ion Beam) cuts, along with EDS and SEM analyses, revealed that Fe (deriving from material transfer) acts as a catalyst on the CKS layer for the tribopads and that zinc sulfides are not present everywhere.

Polymer composite coatings subjected to sliding wear under simulated lunar temperature and dust conditions

Due to the detrimental effect of lunar dust on tribological components, it is imperative to develop bearing materials and surfaces which can survive and mitigate dust at the interface while operating under lunar environmental conditions. This issue is poised to become more significant in the near future, with lunar exploration evolving beyond the short probing missions of the Apollo era. Therefore, this study aims to investigate the combined effect of temperature and lunar dust on the tribological performance of aromatic thermosetting copolyester (ATSP) and polyether ether ketone (PEEK) -based polymer composite coatings from −150 to 110 °C. The experiments were conducted using a flat pin-on-disk configuration under dry sliding conditions, sliding speed of 0.25 m/s, 17.5 MPa contact pressure, and nitrogen gas environment. It was found that metal-on-polymer coating sliding results in dust embedment and accumulation on the softer material, which yields high friction and two-body abrasive wear. The chemical analysis of transfer film on the metal pin surface indicated a mixture of dust and polymer phases, which increased with increasing temperature, and thus resulted in deteriorated tribological performance. Self-mating polymer coatings yielded lower friction coefficient and wear due to a better dust mitigation resulting in three-body wear at the interface. The ATSP-based coatings showed higher wear resistance at all temperatures, particularly under self-mating sliding condition.

The influence from PTFE on surface and sub-surface damages of glass fiber reinforced PPS

Polymer composites are common materials for tribological components, even at relatively high operating temperatures. One advantage is the possibility to add low friction additives, such as PTFE, to the base material. In this paper the influence of such additives was studied, with focus on surface and sub-surface damages. The polymer composites were PPS with glass fibers (PPS-F), PPS with glass fibers and PTFE (PPS-L) and PEEK with carbon fibers, graphite and PTFE (PEEK-L). A reciprocating ball-on-disc test set-up, with ball bearing steel balls as counter material, was used with 5 N and 15 N normal load. The tests were run for 2,000 and 10,000 cycles in room temperature, 80 °C and 120 °C. PPS-F showed high friction (µ ≈ 0.4–0.5) and severe surface damage of both the polymer and the counter surface. Sub-surface cracks, detachment of fibers from the polymer and a deformed surface layer was revealed, when studied in cross section. The load and temperature had negligible effect on the friction, however a higher temperature resulted in more surface damage of the PPS-F. PPS-L and PEEK-L showed relatively low friction (µ ≈ 0.1) and superficial surface damage. XPS analysis revealed a thin tribofilm of PTFE in the wear track for PPS-L.

Development of a Space Grease Lubricant with Long-Term-Storage Properties

Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained increasing attention recently. The term addresses the time-dependent stability of a lubricant under static conditions, which can mean chemical degradation processes such as oxidation on the one hand, but also the physical separation of oil and thickener in heterogeneous lubricants like greases. Due to the extended storage periods of lubricated components on-ground but also during a space mission for several years, it has to be ensured that a lubricant is still functional after LTS. This article depicts the development of a space lubricant grease with LTS properties. Firstly, LTS requirements and methods for their assessment are discussed. In the following, a systematic approach towards the design of a grease formulation compatible with LTS is described. Finally, the manufacturing of prototype formulations and their broad characterization by means of LTS behaviour, outgassing, and tribological performance is presented.

The Influence of Non-Gaussian Roughness and Spectral Properties on Mixed Lubrication for Heavily Loaded Counterformal Contacts

The impact of non-Gaussian height distribution and spectral properties on the lubrication performance of counterformal (point) contacts is quantitatively studied (film parameter, Λ, and asperity load ratio, La) by developing a mixed lubrication model. The Weibull height distribution function and power spectral density (PSD) are used to generate artificial surface topographies (non-Gaussian and Gaussian, isotropic), as these surface topographies are found in many tribological components. The set of variables needed to parametrize and their effect on mixed lubrication is discussed, including the shape parameter, the autocorrelation length, the wavelength ratio, and the Hurst coefficient. It is revealed that a rough surface with a lower shape parameter exhibits higher hydrodynamic lift. The spectral properties (the autocorrelation length and the wavelength ratio) of rough surfaces significantly affect the film parameter and the hydrodynamic and asperity pressures. The film parameter is slightly influenced by the Hurst coefficient.

Long-Term Stable Superlubricity Coatings Enabled by the Interaction between the Polydimethylsiloxane Brush and Silicone Oil.

Recently, materials with superlubricity captured widespread attention on account of their great potential in energy savings and environmental protection. However, certain issues still remain to be solved for the traditional materials, such as the dependence on strict conditions and an unstable superlubricity state. Herein, a long-term stable superlubricity coating was prepared using a low-cost and simple method via an epoxy-based coating with polydimethylsiloxane (PDMS) brushes under silicone oil (SO) lubrication conditions. Compared with the pure epoxy resin matrix, the friction coefficient and wear track width of the superlubricity coating with the optimal amount of 6 wt % PDMS are reduced to 0.006 and 50.9 μm (reduced by 10-fold and 5.6-fold decrease, respectively). In addition, the coating can maintain a stable superlubricity state during a 5 h tribological test. The superlubricity of the coating results from the synergistic lubrication effect of the PDMS brush and SO. First, PDMS brushes with high-stretched conformation due to the swelling effect of the SO can significantly reduce friction. Second, a stable oil film is generated between the contact surfaces, which significantly improves the frictional performance. Moreover, the PDMS incorporated into the coating matrix, along with oil-swelling PDMS brushes on the surface, is highly beneficial for enhancing corrosion resistance of the epoxy resin matrix. Such an epoxy-based coating with long-term stable superlubricity is considered as a potential lubricating and protective surface for tribological components for long-term service.

Tribological properties of CNT-filled epoxy-carbon fabric composites: Optimization and modelling by machine learning

Polymer matrix composites reinforced with fibers/fillers are extensively used in several tribological components of automotive and boating applications. The mechanical performance of polymer composites improves by incorporating nanofillers as secondary reinforcement. The present research work fabricated carbon fabric-reinforced epoxy composites using the hand layup. The carbon fabric-reinforced polymer composites were fabricated with 0.1 wt%, 0.2 wt%, and 0.5 wt% of carbon nanotubes (CNT) fillers as secondary reinforcement. Tribological properties of carbon fabric-reinforced epoxy composites filled with CNT have been carried out using a pin‐on‐disc method. Adding fillers significantly improves the tribological behaviour of the carbon fabric-reinforced epoxy composites by reducing wear rate and coefficient of friction. The large surface area of interaction due to the higher aspect ratio of CNT shows improved adhesion between epoxy matrix and carbon fabrics. It improves the various mechanical and tribological characteristics of composites—also, an analysis of worn surfaces is carried out to analyze the wear mechanisms using scanning electronic microscopy. The research employs a combination of experimental analyses and machine learning (ML) techniques to explore the wear resistance, hardness, and predictive modeling of volume loss in the composites. The hyperparameter fine-tuning of ML algorithms, including Random Forest (RF), k-Nearest Neighbors (KNN), and XGBoost, demonstrates superior predictive capabilities, particularly with RF. The study bridges material science, ML, and practical applications, contributing valuable insights for developing advanced composite materials.

Surface Life Modelling of Tribological Components – From Surface Roughness to Bearings and Gear Life

Surface Life Modelling of Tribological Components – From Surface Roughness to Bearings and Gear Life

Investigation on wear behaviour of TiC/Co/Y2O3 metal matrix composite coating developed on AZ91D Mg alloy by plasma transferred arc cladding process

A high wear resistant TiC/Co/Y2O3 composite coating was synthesized on the surface of AZ91D Mg alloy by plasma transferred arc (PTA) coating process. The results showed that the major phases present in the coating were TiC, Al2O3, Y2C3, Y2Al, TiCo3 and Co2Ti. The coatings had a sound metallurgical bonding to AZ91 Mg alloy substrate. The maximum average surface hardness of TiC/Co/Y2O3 composite coated layer was found to be around 3374 HV0.05, which is about 49 times higher than that of AZ91D Mg alloy (68 HV0.05). The wear rate of the coatings was 8.48 × 10-8 g/N-m, which was reduced about seven times as compared to AZ91D Mg (58 × 10-8 g/N-m). It was concluded that the wear resistance of TiC/Co/Y2O3 composite coating was enhanced as compare to the AZ91D Mg alloy. This type of TiC/Co/Y2O3 coating may increase the application of AZ91D Mg alloy in the automotive industries for manufacturing of tribological components.

Fundamental relationship between rolling contact fatigue driven surface damage and torsional fatigue

This paper presents fundamental findings on equivalence of rolling contact fatigue (RCF) driven surface damage and torsional fatigue modes of failure. Fatigue experiments were conducted for both modes of failure using AISI 4130 case carburized steel specimens. A Thrust Bearing Surface Pitting Rig (TBSPR) was designed and developed to perform RCF tests on flat test specimens using thrust ball bearings. The experiments were conducted in boundary lubrication regime, simulating the contact conditions in tribological machine components. The current investigation presents a novel approach where the effect of contact pressure and number of fatigue cycles on the initiation of surface damage was characterized by surface profilometry of the wear track after each test to generate a stress-life (S-N) map. The S-N map provides unique insights to early detection of RCF driven fatigue damage. The S-N map was utilized to generate the surface damage S-N curve. Torsional fatigue experiments were conducted on the same material, and the S-N curves of both failure modes were compared. The comparison shows key similarities between the two S-N curves, as they differ by a simple scaling factor. This investigation demonstrates that RCF driven surface damage characteristics can be predicted by conducting much simpler, and faster, torsion fatigue tests. This paper also presents a novel methodology to determine contact pressures to avoid incipient micropitting/microdenting damage.

An investigation into various failure criteria on rolling contact fatigue through an improved probabilistic model

This work presents an improved probabilistic continuum damage mechanics (CDM) finite element (FE) model to simulate the degradation of material as a function of cycle in order to estimate rolling contact fatigue (RCF) life of critical tribological components. Traditionally, CDM-FE models consider the shear reversal to be the damage causing stress in RCF; however, in this investigation, the CDM-FE model also considers the octahedral shear stress, the maximum shear stress, the Fatemi-Socie criteria, and the Dang Van multi-axial fatigue parameter as failure criteria. The critical damage material parameters (σr and m) were obtained from open literature torsion fatigue results. Further, to enable a probabilistic CDM-FE model, the critical damage material parameters (σr and m) were described via a distribution as opposed to fixed values. This allows for the variation of a material’s resistance to fatigue that is present in both torsion and rolling contact fatigue to be captured. Forty unique material microstructure models were created using Voronoi tessellations to capture the random pathways for crack growth. RCF simulations were conducted at five contact pressures between 1.0 GPa and 3.4 GPa. Regression analysis between contact pressure and cycles to failure for each of the failure criteria yielded five unique predictive fatigue life equations, one for each failure criteria investigated. These fatigue life equations were then compared to Lundberg-Palmgren theory considering appropriate material and lubrication factors. The results demonstrated that the Fatemi-Socie and shear stress reversal failure criteria compared favorably to Lundberg-Palmgren theory. Notably, the Fatemi-Socie criteria exhibited closer agreement with Lundberg and Palmgren theory at higher contact pressures, in contrast to the shear reversal criteria.

High-performance tribo-components through combination of materials on the macroscale

The tribological performance of four different tribocomposite assemblies was comparatively investigated by sliding against a steel ring on a block-on-ring tribometer in a wide range of surface pressure (p) and sliding velocity (v), and the experimental results were described by a model. The results show that the friction coefficient in the stationary friction phase and the specific wear rate of the composite assemblies tend to follow the superior partner. Surprisingly, it is also found that the pv-load limit can be shifted to the higher pv-limit of the better partner. The results of the present work clearly show that the macroscopic combination of tribocomposites can be an excellent approach for the fabrication of tribological components, e.g. bearings, with long lifetime, high energy and eco-efficiency.

Tribological considerations for failure restoration and maintenance of radial plunger pump against friction and abrasive wear behavior by microwave cladding of Ni-Graphene

Clean and efficient manufacturing techniques are in great demand in modern industrial facilities. New methods are being developed which are cleaner, environment-friendly, economical, and have better mechanical properties, among others. Due to hot corrosion, Tribological components are often subjected to wear and tear. Graphene (Gr) is a promising material with microwave absorption performance due to its self-lubricating properties, low density, and cementite (Fe3C) formation capabilities with iron. This work examined the effect of self-lubricating behavior and surface hardening of plungers of Austenite alloy by Ni-Gr cladding and glazing. Using silicon carbide abrasive media, a pin-on-disc wear tester was utilized for abrasion testing. Scanning Electron Microscopy (SEM), and X-ray diffraction (XRD) analysis supplemented with a microhardness test were performed to measure the improvement in the properties of clad samples. The results showed that temperature variation influences phase change and mechanical properties. The Ni-Gr cladding showed dense eutectic microstructure at 750° C. XRD’s results revealed that the disintegration of the cladding layer is reduced due to heat treatment along with the generation of the Fe3C phase. In addition, the deposited specimen confirmations maximum wear resistance and hardness characteristics with a minimum wear rate at 750 °C, just above the steel's first critical temperature.

Study of mixed-EHL traction coefficient between cam-roller follower interface under different operating conditions

In heavy duty vehicles, high power density (power throughput/weight) is desired to achieve the high fuel efficiency. The increasing demand of high power output results in harsh operating conditions (high load, high surface temperature) in which tribological components such as cam/roller follower are enforced to operate. The traction between cam-roller interface highly depends on the contact conditions between roller-pin interface, and the slippage between roller-pin interface may leads to high friction coefficient between cam/roller follower. In this work, a simplified mixed-EHL model is developed to study the traction between the cam/roller follower interface by considering coupling between roller-pin and cam-roller contacts. The develop mixed-EHL model is validated with published results in order to verify the correctness of the model. It is found that slide-to-roll ratio (SRR) increases with an increase in load torque. The effect of surface roughness on performance parameters is presented. Surface maps of SRR, lambda ratio and asperity load ratio for feasible range of maximum contact load and camspeed are also discussed.

Lubricated sliding wear of gear material under electrification – A new approach to understanding of the influence of shaft currents in the wear of EV transmissions

Electrification of drivelines of electric vehicles (EVs) can give rise to damaging shaft voltages/currents that can potentially impair the tribological performance of sliding and rolling elements in these driveline systems. In fact, previous research has shown that the existence of shaft voltages/currents in electric machines is indeed highly detrimental for the service life of tribological components of EVs. Such currents/voltages originate from magnetic flux asymmetry, inverter-induced voltage and triboelectrification and may also interfere with the normal sliding condition of other electrically conductive tribological components connected to the electric motors in addition to those that are comprised in the driveline, e.g., gears. In the past, the influence of shaft voltages/currents in gear systems has been explored scarcely. Accordingly, this work aims to investigate specifically the lubricated sliding friction and wear behavior of gear materials under the influence of DC electrification. For this, many tests were conducted on a gear material in a two-electrode-cell-based pin-on-disc tribometer representing the sliding contact of a gear interface. The tests were run under different currents (0, 1.5 and 3 A) and using different lubricants (pure mineral base oil, gear oil and transformer oil). The differences in sliding contact temperature, coefficient of friction (CoF), wear volumes and underlying mechanisms, as well as the chemical changes occurred in the lubricating oils by electrification are analyzed and discussed. Overall, the results confirmed that electrification can indeed have a strong influence on friction and wear of gear materials besides increasing contact temperature and thus accelerating the oxidation at the sliding interfaces for all the lubricants. The increase in wear is most likely due to three-body abrasion caused by increased oxidation and/or oxide-based debris formation under electrification. CoF was found to decrease by electrification, which was ascribed to the formation of a larger wear scar (that reduced contact pressure) and continuous replenishment of an oxide layer affording Lower Friction To Sliding Surfaces.

Synthesis and experimental evaluation of tribological behavior of fly ash filled E- glass fiber reinforcement epoxy composites using Taguchi method

The expanding field of composite materials requires the adoption of inexpensive, readily accessible waste byproducts as reinforcement. The tribological components of modern industrial uses for PMCs are what make them so well-liked. In this study, an epoxy matrix was used. Composites are made by hand lay-up and use fly ash as reinforcement. This research is based on an analysis of the wear behaviour of a fly ash epoxy composite under different conditions, including filler loadings of 4 wt%, 8 wt%, 12 wt%, and 16 wt%, normal loads of 10 N, 15 N, 20 N, and 25 N, sliding velocities of 1.0 m/s, 1.5 m/s, 2.0 m/s, and 2.5 m/s, and sliding distances of 300 m, 600 m, 900 m, and 1200 m. The wear behaviour of a pin-on-disc wear testing machine was investigated using a Taguchi L16 orthogonal array under dry conditions at room temperature. The sliding distance was discovered to have the highest influence on composite wear at 36.0815 %.

Design, fabrication and characterization of MoS2self-lubricating pure MoS2Coatings for space applications using PVD magnetron sputtering

Tribological components cost just a fraction of the whole spacecraft, but they often lead to failures that partially or completely disrupt the spacecraft. Mechanical components used in space applications have to withstand extreme and severe environmental conditions such as very high or very low cryogenic temperatures, high vacuum, corrosive elements and radiation. MoS2 is the most widely used lubricating material in space applications. It possesses a lamellar structure with strong covalent bonds within layers and simultaneously weak van der Wall’s interlayer bonds, resulting in easy shearing of the crystals in the direction parallel to the basal planes, hence acting as a good solid lubricant.In this research, a thin film nano scale coating of MoS2 was deposited on steel using Physical Vapour Deposition (PVD). The PVD technique used was the RF magnetron sputtering process. Material characterization was performed using X-Ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy. According to the results, the developed MoS2 nano coatings have a polycrystalline structure with basal planes that are oriented perpendicular to the substrate surface.