Tribological Applications Research Articles

Characterization of atmospheric pressure plasma deposited (APPD) coatings to improve the friction behavior of thermoplastic surfaces

Achieving a significant friction reduction is crucial for using thermoplastic materials as substrates in tribological applications and presents an eligible alternative to the use of light metals. In this study, previously developed MoS2/graphite/zinc composite coatings, applied by an atmospheric pressure plasma deposition (APPD) process, were investigated to extend the understanding of their characteristics and the influence of the process and environmental parameters on friction behavior. Tribological tests were conducted in ambient conditions and at elevated temperatures (110 °C) to study the friction behavior under application-oriented conditions. The presence of atmospheric oxygen during the deposition process was shown to influence the durability of the coatings, which motivated the application of an inert gas atmosphere for the coating deposition. A novel shrouding plasma nozzle was introduced, which further lowered the friction coefficients. The oxidizing effect of the plasma spray deposition was studied with X-ray photoelectron spectroscopy to investigate the strong impact of the deposition current on the friction behavior and durability of the deposited coatings. Coating composition, morphology, and the effects of the tribological testing were evaluated using optical microscopy, 3D surface measurements, scanning electron microscopy, X-ray diffraction, and nanoindentation. The fabricated coatings with thicknesses in the 10 μm range and good adhesion on the polyamide substrate were stable under extended testing durations and at elevated temperatures and accomplished a significant friction reduction compared to the uncoated polyamide. Thus, APPD-fabricated MoS2/graphite/zinc coatings represent an excellent candidate for low-friction applications of thermoplastic substrates.

Tribological Properties of Composites Based on Single-Component Powdered Epoxy Matrix Filled with Graphite.

Composites based on powdered single-component epoxy matrix are an alternative technological solution for composites produced using liquid epoxy resins. This article describes in detail the process of producing graphite-reinforced composites for tribological applications. The advantages and disadvantages of technological processes where the matrix is a single-component epoxy powder were demonstrated, and the properties of the obtained materials were examined. A series of composite materials with the graphite filler with sizes below 10 μm and below 45 μm and weight additions of 5, 10, 20, 30% were produced. Mechanical tests and tribological tests conducted with the pin-on-block method were performed, and the mechanism of tribological wear was described. The conducted research allowed us to conclude that the incorporation of graphite, regardless of particle size, above 10% by weight results in a significant reduction in the friction coefficient (approximately 40-50% lower than in unfilled epoxy resin), which is beneficial in the production of cheap self-lubricating materials.

X-ray peak broadening analysis of Bougainvillea glabra assisted ultrasonic exfoliation of h-BN sheets

In this study, h-Boron Nitride (h-BN) nanosheets have been successfully exfoliated using Bougainvillea flower extract and ultrasonication process. The microstructural parameters such as microstrain, stress, and energy density were calculated using Williamson–Hall analysis. The time of ultrasonication and post-annealing temperature significantly alter the microstructure parameters such as crystal size, microstrain, stress, and energy density upon sonication. The lattice constants such as a-axis and c-axis, cell volume, and bond length did not alter significantly which confirms that there is no crystal structure deformation upon sonication and annealing processes. FESEM result revealed that exfoliation of h-BN and ultrasonication duration greatly influenced the exfoliation. Raman and FTIR studies confirm the pure phase of h-BN without secondary impurities. A simple ultrasonication process would effectively exfoliate h-BN layers and this could be used for tribological applications to reduce the friction between rubbing surfaces.

Facilitating macroscopic superlubricity through graphene oxide nanosheet additives in phosphoric acid

The field of superlubricity is garnering significant global interest amid the ongoing energy crisis. Various liquids can achieve superlubricity under ambient conditions; however, this limits their applications, such as in acidic environments. Consequently, enhancing anti-wear properties and reducing the coefficient of friction (COF) have become pressing challenges. Graphene-based materials are being extensively studied for tribological applications, attributed to their unique molecular structures and lubricating properties, often serving as lubricating additives to significantly reduce COF. In this study, graphene oxide (GO) nanosheets were utilized as lubricating additives in phosphoric acid (H3PO4; pH = 1.5) to explore lubrication enhancement in acidic environments. An ultralow COF of 0.001 was achieved, accompanied by reduced surface roughness and increased contact pressure (by 96.42 %), following the lubrication with GO-H3PO4. The reduction in COF post-lubrication with GO-H3PO4 is ascribed to three primary factors: the formation of a tribofilm via chemical reactions (comprising silica and phosphorus oxide layers), the hydrogen bond effect leading to a hydrated water layer with low shear strength, and the adsorption of GO nanosheets on the friction surface, facilitating friction transfer from Si3N4/Si3N4 to GO/GO.

Nano lubricants in machining and tribology applications: A state of the art review on challenges and future trend

Nanofluids are a unique class of fluids generally prepared by adding nanosized particles to different types of base fluids, such as water, oil, etc. When nanoparticles are added to the base fluids, their thermophysical parameters like viscosity, heat transfer characteristics, and thermal conductivity are improved and provide good results. For this reason, the demand for fluids enriched with nanoparticles has considerably increased in the manufacturing sector. This comprehensive state-of-the-art review covers nanolubricants' role in friction reduction, wear resistance, and machining efficiency applications. Initially, the lubricants and their properties are revealed in the introduction section. Then, the different types of nanoparticles, their basic structure, and their different applications in machining and tribology are portrayed in different sections. In addition, it provides a comprehensive analysis of the difficulties related to nanofluids and their utilization in machining and tribology. Ultimately, this evaluation provides final comments on the latest advancements in both the academic and industrial sectors, as well as a strategy for future expansion. The results indicated that the fluids loaded with nanoparticles had a beneficial effect in lowering friction and temperature at the primary contact zone.

Exploring the Impact of Spray Process Parameters on Graphite Coatings: Morphology, Thickness, and Tribological Properties

This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow rates, followed by analysis of their morphological characteristics, roughness, thickness, coefficient of friction (COF), and wear behavior. The results revealed distinct differences in the coating morphology based on flow rate, with low-flow-rate coatings exhibiting a porous structure and higher roughness, while high-flow-rate coatings displayed denser structures with lower roughness. A COF as low as 0.09 was achieved, which represented an 86% reduction compared to uncoated steel. COF and wear track measurements showed that thickness was influential in determining friction and the extent of wear. Flow rate dictated the coating structure, quantity of transfer film on the ball, and the extent of graphite compaction in the wear track to provide a protective layer. SEM and elemental analysis further revealed that graphite coatings provided effective protection against wear, with graphite remaining embedded in the innermost crevices of the wear track. Low flow rates may be preferable for applications requiring higher roughness and porosity, while high flow rates offer advantages in achieving denser coatings and better wear resistance. Overall, this study highlights the importance of optimizing graphite concentration and spray flow rate to tailor coating morphology, thickness, and tribological performance for practical applications.

Molecular Dynamics Simulation on Polymer Tribology: A Review

A profound comprehension of friction and wear mechanisms is essential for the design and development of high-performance polymeric materials for tribological application. However, it is difficult to deeply investigate the polymer friction process in situ at the micro/mesoscopic scale by traditional research methods. In recent years, molecular dynamics (MD) simulation, as an emerging research method, has attracted more and more attention in the field of polymer tribology due to its ability to show the physicochemical evolution between the contact interfaces at the atomic scale. Herein, we review the applications of MD in recent studies of polymer tribology and their research focuses (e.g., tribological properties, distribution and conformation of polymer chains, interfacial interaction, frictional heat, and tribochemical reactions) across three perspectives: all-atom MD, reactive MD, and coarse-grained MD. Additionally, we summarize the current challenges encountered by MD simulation in polymer tribology research and present recommendations accordingly, aiming to provide several insights for researchers in related fields.

Self-dispersed molybdenum disulfide quantum dot/graphene crumpled ball as efficient high temperature lubricant additive

Inorganic nanoparticles have been proved as powerful lubricant additives at elevated temperature. However, the tribological properties are inevitably impaired due to poor dispersion and insufficient high temperature resistance of organic matter modified nanoparticles. Here, we prepare a self-dispersed molybdenum disulfide quantum dot/graphene crumpled ball (MGCB) comprising molybdenum disulfide quantum dot uniformly interspersed on the wrinkled graphene ball. The crumpled ball composite possesses excellent dispersity in polyalkylene glycol base oil without depending on surface modifiers. Compared with the conventional phosphate esters lubricant, our results indicate MGCB could vastly improve the lubrication performance of polyalkylene glycol with an extremely low concentration (0.05 wt%) at elevated temperature (150 °C), showing a friction reduction of 47% and a wear reduction of 30% compared with the conventional phosphate esters lubricant (tricresyl phosphate, TCP). This is because crumpled ball potentiates synergistic lubrication effect within the boundary lubrication. Overall, we envision our designed self-dispersed MGCB has significant potential in tribological application at elevated temperature.

Surface optimization of trapezoidal thread spindles—tribological analysis and application

Trapezoidal threaded spindles are ideal for supporting heavy loads and are therefore frequently used in heavy-duty lifting systems. Both the forming thread rolling process and the machining thread whirling process can be used to manufacture these lead screws. In order to improve the low efficiency of trapezoidal screw drives, it is crucial to understand and minimize friction losses. As part of a cooperation project between the Institute of Production Engineering and Machine Tools (IFW) and Bornemann Gewindetechnik, research was carried out into adapting the whirling process to optimize the tribological properties of threaded spindles. The process developed makes it possible to reduce the coefficient of friction in trapezoidal screw drives and thus also the required torque. By using whirled microtextures, the friction loss can be reduced by 25.5% and adhesive wear can be significantly reduced.

The Impact of Volume Fraction and Nanoparticles in the Flow of Nanofluids along the Boundary Layer Over a Flat Plate

Introduction: The forced convective, steady, viscous, nonlinear boundary layer flow of a two-dimensional problem over a flat plate with heat transfer nanofluids. The flow is laminar. Two different types of nanoparticles, namely, Titanium dioxide () and Silver are used to prepare nanofluids with base fluid is chosen as water. Nanofluids has a large number of applications in the area of biomedical, cooling and tribological applications. Objectives: To study about the effect different nanoparticles and their volume fraction in the flow of nanofluids along the boundary layer over a flat plate. Analyse the changes in the viscosity, density, specific heat capacity, thermal conductivity, Prandtl number, skin friction coefficient and Nusselt number. Methods: The flow of the fluid that are governed by the PDEs that are nonlinear are transformed into the ODEs that are nonlinear by employing similarity transformations, which then solved by the use of MATLAB bvp5c solution procedure. Results: Both thermal conductivity and heat transfer coefficient increases with the increase in the volume fraction of the corresponding nanoparticle. Also, Silver-water nanofluid has the high thermal conductivity and heat transfer rate when compared with Titanium dioxide-water nanofluid. Conclusions: Silver water nanofluid surpasses titanium dioxide water nanofluid in terms of thermal conductivity and heat transfer rate. Moreover, the physical attributes like viscosity, density, and thermal conductivity of nanofluids escalate proportionally with the volume fraction of nanoparticles. Conversely, specific heat capacity and Prandtl number exhibit an inverse relationship with the volume fraction of nanoparticles, decreasing as it increases.

Microstructural and mechanical properties of microwave sintered bulk titanium nitride nanoceramics

In the present work nano-sized TiN powders were consolidated and sintered in nitrogen, argon and air using microwave power of 900 W at frequency 2.45 GHz. Green compacts were exposed to microwave energy, and heated at an in-situ temperature of 1500 °C without holding time. The relative density achieved was ∼92 %. X-ray diffraction analysis showed presence of TiN as the dominant major phase. The microstructures indicate that the sintered samples retained their nanocrystallinty, though aggregates comprising clusters of nanoparticle was noticed with size in the range of 80–400 nm due to high heating rate. Micro indentation assessment indicates average Vickers hardness of 15.2 ± 0.5 GPa. The lengths of cracks originating from the indentation edges were measured; the indentation fracture toughness were obtained between 4.0 and 4.5 MPa.m1/2. The observed properties indicate the suitability of the sintered material in tribological applications.

Wear-resistant and adherent nanodiamond composite thin film for durable and sustainable silicon carbide mechanical seals

In response to environmental concerns, there is a growing demand for durable and sustainable mechanical seals, particularly in high-risk industries like chemical, petroleum, and nuclear sectors. This work proposes augmenting the durability and sustainability of silicon carbide (SiC) ceramic seals with the application of a nanodiamond composite (NDC) film through coaxial arc plasma deposition (CAPD) in a vacuum atmosphere. The NDC coating, with a smooth surface roughness of Ra = 60 nm as substrate, demonstrated a thickness of 1.1 μm at a deposition rate of 2.6 μm/h. NDC film has demonstrated exceptional mechanical and tribological characteristics, such as a hardness (H) of 48.5 GPa, Young's modulus (E) of 496.7 GPa, plasticity index (H/E) of 0.098, and fracture toughness of H3/E2 = 0.46 GPa, respectively. These NDC films showcased commendable adhesion strength (>60 N), negligible wear, and low friction (≤0.18) during dry sliding against a SiC counter material. Raman analysis has confirmed the nanocomposite structure of NDC film, emphasizing the role of highly energetic carbon ions in enhancing film adhesion by forming SiC intermetallic compounds at the interface through the diffusion of silicon atoms from the substrate into the films. The abundance of grain boundaries and rehybridization of carbon sp3 to sp2 bonding is perceived to improve tribological performance. CAPD excels in synthesizing long-life eco-friendly NDC coatings for durable and sustainable mechanical seals, featuring smooth surfaces, superior adhesion, outstanding hardness, and wear resistance, making them high potential candidates for various tribological applications.

Tunable amorphous carbon films formed on ultralow wear, Pt–Au alloys

The mechanocatalytic formation of carbonaceous films at the interface between sliding metallic contacts is simultaneously advantageous for reducing friction and adhesion in several tribological applications and detrimental for electrical contacts as they can induce device failure by increasing the contact resistance. Yet, remarkably little is still known about the chemistry, structural and mechanical properties, and tunability of these interfacial layers. In this study, we performed contact pressure-dependent tribological experiments in dry nitrogen containing trace organics on four, nanocrystalline Pt–Au alloys ([Au] from 0 at.% to 10 at.%) – a promising class of alloys for ultralow wear and electrical contact applications. The ex-situ, multi-technique characterization results did not only provide insights into the chemical nature and mechanical behavior of the mechanocatalytic, carbon-rich films formed on Pt–Au surfaces, but also revealed the interplay between catalytic and mechanochemical tribofilm formation controlled by the composition-dependent electronic structure of the Pt–Au substrate and the applied contact pressure. The results of this work provide guidelines for tailoring nanocrystalline alloys to control their mechanocatalytic activity on the basis of variations of the alloy mechanical properties and element's electronic structure with the alloy stoichiometry.

Exploring the Friction and Wear Mechanisms of Nickel Titanium Alloy Fabricated by Laser Powder and Wire-Based Directed Energy Deposition

The NiTi alloy has attracted significant interest owing to its notable wear and corrosion resistance, suggesting the significant promise of utilizing additively manufactured NiTi alloys in tribological applications. In this study, dry sliding wear tests with sliding velocity of 0.1 m/s for total distance of 250 m at room temperature, 50 °C, 100 °C, and 200 °C were carried out on samples of NiTi alloy samples fabricated using laser powder and laser wire directed energy deposition (LP-DED and LW-DED) processes. Enhanced friction and wear behavior of LP-DED samples were captured at lower temperatures due to higher hardness and the stable dominating NiTi B2 austenite phase in the sample microstructure as confirmed from x-ray diffraction (XRD) analysis. Accumulated transferred material at lower temperatures played a crucial role in modifying the wear mechanisms. However, at higher temperatures both LP-DED and LW-DED samples presented similar wear mechanisms.

Investigation on preparation and tribology of poly ether ether ketone nanocomposite with transition metal doped zirconium dioxide

Composite materials are currently one of the most active study fields in modern technology. Their promising properties make them appropriate for a wide range of industrial applications including aerospace, automotive, construction, sports, bio-medical, and many more. These materials have amazing structural and mechanical features such as high strength-to-weight ratio, resistance to chemicals, fire, corrosion, and wear, as well as being cost-effective to produce. Poly-ether-ether-ketone (PEEK), a high performance polymeric materials, is increasingly being employed to replace metal elements in car engines and transmissions. Zirconium oxide (ZrO2), often known as zirconia, is a high-tech ceramic substance that is widely employed in the manufacture of various hard ceramics. The various physical and chemical properties of ZrO2 have been properly tailored for a given use by inserting transition metals (dopants) into the ZrO2 crystalline structure. In this work, the nano-composite of PEEK and transition metal doped Zirconium Dioxide is prepared. The composite was subsequently subjected to vital characterizations and tribological testing. The characterization validated the amalgam of modified ZrO2 with PEEK. The investigation has shown that PEEK reinforcement with modified ZrO2 has desired qualities for use in tribological applications

Experimental studies on mechanical properties of Al-7075/TiO2 metal matrix composite and its tribological behaviour

This study explores the fabrication and characterization of an Al-7075/TiO2 metal matrix composites (MMCs) through stir casting, varying TiO2 contents from 2% to 10%. Various tests, including tensile, hardness, and elastic indentation modulus testing, dynamic mechanical analysis, microstructural evaluation, and XRD, were conducted. Tribological analysis involved tribo-pairs of an EN31 disc and a smooth MMCs pin, using a high-temperature Pin-on-disc setup. Microstructural analysis of Al-7075/TiO2 MMCs revealed uniform TiO2 distribution, grain refinement, and enhanced mechanical properties, with XRD confirming structural changes. Tensile tests showed improved ultimate force and stress with increasing TiO2 content, indicating potential for high-strength applications. Hardness assessments demonstrated progressive improvements in Martens, Elastic Indentation, and Vickers Hardness, highlighting the material's suitability for critical wear and tribology applications. The composites exhibited enhanced damping flexural characteristics, especially with 8% TiO2. Maximum and minimum modulus values are reported as 98.9 GPa at 25 °C and 77.3 GPa at 350 °C for 8% TiO2 mix MMC. Tribological performance was improved with lower COF values and wear rates. At elevated temperatures, the wear behavior varied with TiO2 content, influenced by factors such as heat generation and localized welding.

Al3+ diffusion-directed assembly of GO-CNTs multi-layered composite coatings: Preparation and tribological performance

To resolve graphene coating's typical problems in tribological applications, including poor interfacial bonding, agglomeration, and low wear resistance, a dimensionally composited coating based on graphene oxide (GO) and carbon nanotubes (CNTs) was successfully prepared by a feasible metal-ion diffusion-directed assembly method. Experiments showed that the Al3+ diffusion-directed assembly method could significantly increase the coating interfacial binding strength, elasticity modulus, and hardness. In addition, the synergistic lubrication of GO and CNTs during friction enabled the Al3+-GO-CNTs5.0 coating to sustain a longer operation duration of 12,900 cycles. This study refers to inducing coordination with metal ions in various valence states and compositing carbon-based nanomaterials in different dimensions, which provides a feasible way to improve the lubricating coating's mechanical and tribological performances.

Dynamics of centipede locomotion revealed by large-scale traction force microscopy.

We present a novel approach to traction force microscopy (TFM) for studying the locomotion of 10 cm long walking centipedes on soft substrates. Leveraging the remarkable elasticity and ductility of kudzu starch gels, we use them as a deformable gel substrate, providing resilience against the centipedes' sharp leg tips. By optimizing fiducial marker size and density and fine-tuning imaging conditions, we enhance measurement accuracy. Our TFM investigation reveals traction forces along the centipede's longitudinal axis that effectively counterbalance inertial forces within the 0-10 mN range, providing the first report of non-vanishing inertia forces in TFM studies. Interestingly, we observe waves of forces propagating from the head to the tail of the centipede, corresponding to its locomotion speed. Furthermore, we discover a characteristic cycle of leg clusters engaging with the substrate: forward force (friction) upon leg tip contact, backward force (traction) as the leg pulls the substrate while stationary, and subsequent forward force as the leg tip detaches to reposition itself in the anterior direction. This work opens perspectives for TFM applications in ethology, tribology and robotics.

High-temperature tribological properties of a novel AlFeCoNiCr–Cr3C2 cermet coatings

Microstructural instability of NiCr–Cr3C2 coating greatly limits its high-temperature tribological applications. In this work, we present a design concept for NiCr alloys based on an enthalpy-guided approach. A novel AlFeCoNiCr–Cr3C2 coating was fabricated using a supersonic plasma spraying followed by annealing. The high-temperature tribological results suggested that, due to the precipitation strengthening of Cr23C6 nano-grains in the interfacial transitions and the high plasticity of the disordered BCC (A2) and FCC (A1) phases in the AlFeCoNiCr alloy, the wear rate of the coating after annealing at 600 °C decreased by 47.6 % compared to the NiCr–Cr3C2 coating. The high density of mesoscopic defects further contributed to the strengthening and plasticity of the coating. After annealing at 900 °C, a net-shaped agglomeration of Cr23C6 and A2 phases accelerated oxidation diffusion and abrasive wear, leading to an increase of wear rate of coating. The produced wear debris mainly came from NiCr2O4, Cr2O3, NiO, Al2O3 and Fe2O3, where the NiCr2O4 was the product from the reaction between the Cr2O3 and NiO phases.

Comparative analysis of the solid lubrication performance - Ti3AlC2 versus Ti3C2Tx coatings

Due to the long-standing use of MAX phase materials since the 1960s and the emergence of MXenes in 2011, both are celebrated for their extraordinary mechano-tribological properties, including layered structures, high mechanical strength, and thermal conductivity. Nevertheless, there remains a crucial research gap in comprehensively comparing their tribological performance under solid lubrication, underscoring the need for an in-depth investigation. To close this research gap, we deposited MAX phase and MXene coatings by spray-coating on stainless-steel substrates. Subsequently, we evaluated their tribological properties, deciphered the underlying mechanisms using linear-reciprocating tribometry and high-resolution material characterizations. Our results demonstrated that the MXene coatings surpass the MAX phase coating in friction reduction by 81.82 %. In terms of wear depth, MXene coating has shown a notably reduced depth compared to both the reference steel sample and the MAX phase coating. Advanced tribochemical analysis indicates that MXenes' superior tribological performance is endorsed by their ability to form a thick, patchy-like transferlayer on the counterbody, which results from their ability to shear and delaminate under acting contact stress. Our study offers a framework for future investigations into utilizing MXene-based materials in tribological applications.