Surface Friction Research Articles

Preparation of HTV silicone rubber with hydrophobic–uvioresistant composite coating and the aging research

Abstract A series of high temperature vulcanization (HTV) silicone rubbers with TiO2 ultraviolet (UV) shielding layer and polytetrafluoroethylene (PTFE) hydrophobic layer were prepared via stepwise spray method. It was found that the hydrophobic PTFE liquid emulsion (PTFEL) could steadily and tightly adhere to the HTV silicone rubber surface by spray method after pre-mixing with permanent room temperature vulcanized (PRTV) silicone rubber during the first step spray. And the subsequent introduction of TiO2 and PTEF solid powder (PTFES) could improve the UV shielding ability and further increase the hydrophobicity of HTV silicone rubber during the second step spray after pre-blending. The accelerated hygrothermal aging process and UV aging process were used to analyze the effect of coating structure and composition on anti-aging performance. And the results indicated that the HTV silicone rubber with PRTV-PTFEL/TiO2-PTFES composite coating showed a favorable UV shielding ability and also possessed an excellent hydrophobicity due to the introduction of low surface energy matter and the building of coarse micro-nano hydrophobic structure. After the aging process, the cracked micro-surface, increased water absorption and decreased mechanical property were displayed for the neat HTV silicone rubber, and these aging phenomena got dramatically improved for PRTV-PTFEL/TiO2-PTFES coating HTV silicone rubber.

Covalently Bonded Heterostructures with Mixed-Dimensional Carbons for Suppressing Mechanochemical Wear of Diamond under Heavy Loads.

Diamond is widely acknowledged as the hardest naturally occurring material. Nevertheless, when exposed to friction against ferrous metals, it is prone to graphitization or amorphization, which limits the utilization of its extremely high hardness and wear resistance. These issues have persisted for decades without an effective solution. Here, we report that a covalently bonded heterostructure with mixed-dimensional carbons as a high-performance solid lubricant could effectively reduce diamond surface friction and mechanochemical wear with excellent load capacity and durability. When subjected to dry friction and heavy loads (20-150 N), the heterostructure exhibited a notable improvement over pristine diamond with reduced friction coefficients and relative wear rates by 22-45 and 67-91%, respectively. Especially under a 20 N load, the relative wear rate was an order of magnitude lower than that of pristine diamond. Additionally, experiments and molecular dynamics simulations revealed that the heterostructure integrated the outstanding properties of diamond (three-dimensional (3D)), nanographite (3D), and graphene (two-dimensional (2D)), resulting in improved lubrication and antiwear performance that could not be achieved by the individual carbon materials. The findings in this work will be beneficial to overcome the ferrous metal forbidden zone of diamond and are expected to expand the applications of engineered diamond surfaces and graphite/graphene in tribology, mechanics, and electronic fields.

Exploring the relevance between load-bearing capacity and surface friction behavior based on a layered hydrogel cartilage prototype

Cartilage is well lubricated over a lifetime and this phenomenon is attributed to both of the surface hydration lubrication and the matrix load-bearing capacity. Lubricious hydrogels with a layered structure are designed to mimic cartilage as potential replacements. While many studies have concentrated on improving surface hydration to reduce friction, few have experimentally detected the relationship between load-bearing capacity of hydrogels and their interface friction behavior. In this work, a bilayer hydrogel, serving as a cartilage prototype consisted of a top thick hydrated polymer brush layer and a bottom hydrogel matrix with tunable modulus was designed to investigate this relationship. The coefficient of friction (COF, μ) is defined as the sum of interfacial component (μInt) and deformation/hysteresis component (μHyst). The presence of the top hydration layer effectively dissipates contact stress and reduces the interface interaction (μInt), leading to a stable and low COF. The contribution of mechanical deformation (μHyst) during the sliding shearing process to COF can be significantly reduced by increasing the local mechanical modulus, thereby enhancing the load-bearing capacity. These results show that the strategy of coupling surface hydration layer with a high load-bearing matrix can indeed enhance the lubrication performance of hydrogel cartilage prototypes, and implies a promising routine for designing robust soft matter lubrication system and friction-control devices.

A Novel Al-Al<sub>2</sub>O<sub>3</sub> Non-Skid Composite Coating with Improved Wear Resistance Fabricated by Twin Wire Arc Spraying

In this study, novel non-skid Al-Al<sub>2</sub>O<sub>3</sub> coatings with improved wear resistance were fabricated using twin wire arc spray (TWAS). TWAS Al coating was prepared as a reference sample and representative TWAS parameters (working distance, process gas pressure, arc current) were controlled to fabricate different Al-Al<sub>2</sub>O<sub>3</sub> coatings. The Al-Al<sub>2</sub>O<sub>3</sub> coatings showed a superior static coefficient of friction and higher surface roughness than the Al coating. The microstructural analysis of the Al-Al<sub>2</sub>O<sub>3</sub> coatings revealed that the coatings contained Al splats, partially-melted Al<sub>2</sub>O<sub>3</sub> particles, fully-melted Al<sub>2</sub>O<sub>3</sub> splats and pores. The porosity and Al<sub>2</sub>O<sub>3</sub> content of the Al-Al<sub>2</sub>O<sub>3</sub> coatings varied with different process parameters. The Vickers hardness of the Al matrix showed a similar value in all samples, which means the deposition phenomena was the same. Ball-on-disc wear test with a Si3N4 ball was used to evaluate the wear resistance of the TWAS coatings. The weight loss of the Al-Al<sub>2</sub>O<sub>3</sub> coatings were only 4.8 ~ 17.0 % of the Al coating, indicating that the wear resistance of the TWAS Al-Al<sub>2</sub>O<sub>3</sub> coatings was superior. The TWAS coatings showed a complex wear mechanism, such as splat wear and abrasive wear. The distributed Al<sub>2</sub>O<sub>3</sub> particles in Al-Al<sub>2</sub>O<sub>3</sub> coating successfully suppressed the abrasive wear of the Al matrix, which contributed to the enhanced wear resistance. The results in this study indicated that the Al-Al<sub>2</sub>O<sub>3</sub> composite coating has potential use as a novel non-skid coating.

Prevalence of Skin Injuries in Beach Volleyball Athletes in Greece.

Background: Skin injuries often affect the sports community. Almost every type of athletic activity is associated with traumatic skin injuries, such as surface wounds, bruising, abrasions, subcutaneous hematomas, blunt trauma, nail injuries, friction burns, and blisters. Methods: The aim of this study was to assess the rates, location sites, and seasons of appearance of skin injuries in beach volleyball athletes in Greece. Seven hundred and eighty-five beach volleyball athletes participated in this study. The average age was 28.4 years. Skin injuries included superficial wounds (erosions, incisions, lacerations), deep wounds, hematomas, nail lacerations, friction burns, and friction blisters. The recorded variables encompassed gender, age, the time of year when athletes might be at higher risk of injuries, and the specific body regions affected. Additionally, data regarding training details such as years of practice, weekly training frequency, and daily training duration were also documented. Results: Incidence rates correlated to gender: (a) superficial wounds (p < 0.001), (b) years of training: hematomas (p < 0.001), and (c) average hours of daily training: superficial wounds (p < 0.001), deep wounds (p < 0.001), and friction blisters (p < 0.001). Conclusions: Although early detection, recognition, and treatment are essential, the prevention of skin injuries can also be linked to health and athletic performance.

Effect of oleic acid modified GO‐LaF3 on lubrication characteristics of 10# white oil

AbstractTo study the synergistic lubricating effects of graphene oxide (GO) and lanthanum fluoride (LaF3), and find a new anti‐wear additive, oleic acid surface‐modified graphene oxide‐lanthanum fluoride (OA‐GO‐LaF3, OGL) composite nano‐additive was prepared by hydrothermal method by using oleic acid as the modifier. The morphology, structure, composition, element valence, thermal stability and tribological properties of nano additives were characterised by a series of modern characterisation methods. Results show that OGL has a higher degree of graphitization, smaller particle size, more homogeneous disperse, higher LaF3 load and stronger thermal stability than that of GL. The tribological properties of OGL which is modified by oleic acid are better than unmodified GL. Analysis of the friction mechanism shows that both OGL and GL can generate LaF3 physical adsorption films through adsorption during the friction process and tribochemical reactions film containing lanthanum compounds, carbon oxide compounds, and iron oxide compounds on the friction surface. These physical adsorption films and chemical reaction film can improve lubrication.

Development of Kirigami‐Patterned Stretchable Tactile Sensor Array with Soft Hinges for Highly Sensitive Force Detection

AbstractFlexible and stretchable tactile sensors are attracted in the fields of soft robotics, wearable electronics, and healthcare monitoring. The sensing performance of tactile sensors is commonly affected by external deformations like stretching, bending, and twisting, thus they may fail to function on deformable object surfaces. This paper presents a stretchable tactile sensor array using kirigami‐patterned structural design and soft hinges to reduce the influences of deformation. The kirigami pattern of sensor array is parametrically studied to achieve the required expansion patterns. Laser engraving is employed to modify the micropillars on the force‐sensitive rubber surface to increase the sensitivity. Characterization tests show that the sensor array has high sensitivity (≈1.49 × 10−1 kPa−1) for force sensing, and the stretching and bending deformation have almost negligible effects on sensing performance. Under 40% stretching or 180° bending conditions, the measured resistance changes (ΔR/R0) is ≈0.03 and 0.06, respectively. To demonstrate the capability of developed sensor array, it is mounted on an expandable balloon surface for force detection. The recorded signals changed less than 1.5% during expanding process while rapidly rose under applied force, which indicated that the sensor array has the potential to effectively function on complex and deforming surfaces.

Friction behavior of 3D printed flexible cavity structure at low-speed condition

This study aims to study the changes in surface friction of flexible cavities produced by 3D printing under different internal pressures. An inflatable flexible air cavity fabricated using 3D printing technology and made of Tough-PLA and TPU95A materials was used as the experimental object. This study conducts low-speed friction tests on flexible surfaces under two conditions: different load pressure and different internal pressure. The experimental results show that under the same load conditions, the average sliding friction force between the contact surfaces with a contact area of only 16 cm2 increases by approximately 1 N as the air pressure increases, while the maximum static friction force increases by approximately 2–6 N. The inflatable cavity changes the friction of the contact surfaces under the influence of different internal air pressures. Through roughness measurements and microphotographs of the contact surfaces under different internal air pressures, it was found that the main reason is that the internal air pressure changes the surface roughness of the contact surface, thereby changing the friction between the contact surfaces. This study demonstrates a novel way to control the friction between flexible material contact surfaces. It has broad prospects and great significance for the future application of 3D printing flexible materials in the contact friction control of robot grippers and flexible joints and the lightweight of brakes.

Hierarchical Lateral Planning With Minimum Curvature Peak for Autonomous Vehicles

Abstract This study focuses on the lateral safety of autonomous vehicles. The aim is to provide greater safety margins for the motion controller under hazardous conditions by improving the planning methods. The proposed lateral planning method employs a hierarchical structure. First, a graph search method that considers road curvature is presented. This method benefits from the design of jump nodes and can generate a safe corridor in real-time by backtracking. Next, a concise and effective optimization problem is constructed in the Frenet frame. It is designed to optimize the path by incorporating the peak, integral, and differential of curvature into the objective function. By solving this problem using CasADi, the path within the safe corridor is obtained. Finally, the proposed planning method is combined with a model predictive motion controller and tested through simulation and experimentation on a real vehicle platform. This planning method has good scalability, adaptability, and real-time performance. Simulation and experimental results show that this method can help avoid exceeding lateral limits of road surface friction, improve path-following accuracy, and enhance the safety of autonomous vehicles in dangerous conditions.

Effect of Micro-Texture on Cutting Performance of PCBN Cutter

The research aimed to delve into the intricate relationship between surface microtexture and the cutting performance of a PCBN cutter. In pursuit of this goal, the study implemented three distinct microtextures on the forefront of the turning tool, each of diverse forms. To comprehensively understand the impact, a 3D model was meticulously constructed for simulation purposes. Subsequently, these microtextures were translated into physical form on the tool’s exterior using laser machining, enabling the researchers to conduct real turning experiments. The experimental phase was designed with precision, maintaining consistent environmental conditions across all tests. The primary focus of these experiments was to investigate the forces generated during the turning process. Additionally, the study explored the stress distribution on the tool’s surface and evaluated the texture of the workpiece after machining. The findings revealed valuable insights into the role of microtextures in altering stress dynamics. Specifically, a tool featuring microtexture on its front exhibited a reduction in stress values, strategically shifting the stress focus from the tool’s tip to the microtexture location on the forefront. Moreover, concerning the texture of the workpiece’s surface post-machining, the tool with parallel groove microtexture demonstrated a noteworthy 21% decrease in surface roughness. The study highlighted the pivotal role of surface microtextures in shaping the performance of a lathe tool. These microtextures were identified as agents capable of modifying the immediate friction between the tool and its chip, thereby diminishing surface friction, cutting force, and post-machining surface roughness. The operational stability of lathe machining was also enhanced through these microtextures. Notably, the microtexture characterized by parallel grooves demonstrated a significant improvement in chip-guiding capacity by aligning with the chip flow direction during cutting. The presented research provided a nuanced understanding of how microtextures on a lathe tool’s surface can be strategically employed to optimize cutting performance, offering potential advancements in the field of machining technology.

Effect of laser surface texturing on friction performance and surface damage of silicon nitride ceramic

ABSTRACT Laser surface texturing (LST) with different patterns was performed on silicon nitride (Si3N4) ceramic. Effect of patterns created by LST on coefficient of friction (COF) and surface damage under dry friction was investigated. Results indicated that fluctuation of COF decreased with the increasing loading force for both un-textured and textured samples. Under the same loading force, COF of Si3N4 ceramic with textured patterns was more stable than the samples with smoothly finished surface. The COF of textured samples was not always lower than that of un-textured samples. This may be caused by differences in the distribution of debris and the continuity of surface contact. The worn surface existed damages of plow and crack. However, peeling was observed on un-textured samples only. The surface damage of textured samples was slighter than un-textured samples. Especially under the high loading force, catastrophic damage appeared on the smooth surface. The worn surface of textured samples still maintained the similar state. This could be mainly due to the more complex friction process on the surface of textured sample. The wear rate of the frictional pair was also studied. The mechanisms of friction process for smooth and textured surface were analyzed.

Modeling the wear of the "diamond-containing mineral ceramics — ceramics" friction pair

Based on the solution of the contact mechanics problem, a model of wear of the "diamond-containing mineral ceramics — ceramics" friction pair is constructed, in which diamond grains in the ceramic matrix are represented as spherical segments of the same radius. The law of distribution of diamond grains in a ceramic matrix is power law. The dependences of grinding productivity and wear rate of diamond-containing tools on the physical and mechanical properties of contacting materials, roughness parameters of friction surfaces and loading conditions are obtained. Keywords:abrasive diamond tools, mineral ceramics, ceramics, contact interaction model, productivity, grinding, wear onvk@mail.ru, alnikbltov@rambler.ru, vnvkv@yandex.ru

Effect of inclined Lorentzian force on radiated nanoflow Williamson model under asymmetric energy source/sink: Keller box method

An asymmetric energy source/sink can be designed to efficiently convert ambient energy into usable forms; this could have applications in micro-/nanoscale power generation, i.e., energy harvesting. The asymmetric energy source/sink and inclined Lorentzian force could be used to control the flow of fluids within these devices. This study numerically investigates the model of a Williamson nanofluid influenced by an angled magnetic force and an asymmetric energy input/output on a stretching surface with a convective wall boundary condition. The partial differential equations connected to the momentum, energy, and concentration equations are transformed into nonlinear ordinary differential equations (ODEs) by applying relevant similar variables. The obtained ODEs are handled by the Thomas algorithm and a finite difference in the Keller box method. A thorough examination of a change in velocity, temperature, and concentration is done for all the relevant parameters. A higher buoyancy ratio parameter lowers the streamline density. As far as the numerical method is concerned, the Keller box method gives the highest convergence value when compared to other methods, so we use this method to investigate the sleeping behavior of the Williamson nanofluid. The energy source decreases the non-Newtonian passing surface friction. The concentration gradient increases for an increasing value of the chemical reaction parameter. A decreased diffusion rate is seen for increasing Brownian number, while the opposite behavior is noticed for the thermophoretic parameter. The wall friction coefficient increases for augmenting We but decreases for the angled Lorentzian force. Except for radiation, energy transfer is high in all other flows, affecting parameters such as A, B, Nb, Nt, and Pr. By controlling the magnetic field, MHD heat exchangers can manipulate heat transfer rates for various industrial applications. In fusion reactors, strong magnetic fields confine hot plasma, and understanding the interaction between the field and heat sources is crucial for efficient energy generation.

Effect of Crusher Arm Position and Surface Friction on the Mechanical Behaviour of a Crusher under Static Conditions

Crushers are utilized to break down or crush various components in industrial applications are subjected to high stresses. The crushing process is carried out by a crusher arm located on the crusher itself. The shape and length of the crusher arm influence the deformation on the arm and the efficiency of crushing process. During the crushing process, stress concentrations occur at the contact regions and especially at the connection location of the crusher arm and the drive shaft. This study examined the connection of the crusher arm at various positions on the shaft and explored variations in stress. Finite element analysis was used in the analyses. The used material is standard steel that behaved elastically. The stresses changed in a way that was not proportional to the movement of the tangential crusher arm towards the center of the shaft. The d=8 mm and d=24 mm locations are the most suitable places to move the crusher arm rather than the tangential position (d=40 mm). The highest stresses occurred at the corners where the shaft and crusher arm connected and formed a stress concentration. The friction effects on the contact surface were also examined and the increased friction coefficient slightly reduced the stress values of the crusher system, but increased the stresses on the crushed object. Only maximum stress levels that are observed at the surface of the beam are mainly considered. The results regarding the crusher arm are discussed in detail.

Study on High-Temperature, Ultra-Low Wear Behaviors of Ti6Al4V Alloy with Thermal Oxidation Treatment

Thermal oxidation (TO) is a simple and economical way to enhance the wear resistance of the Ti6Al4V alloy. The TO temperature has a very important effect on the tribological properties of the TiO2 layer formed. However, the impact of the oxidation temperature on the high-temperature tribological behavior of a TO-treated Ti6Al4V alloy is not clear. Therefore, the Ti6Al4V alloy was oxidized at 400 °C, 600 °C, and 700 °C for 36 h, and the sliding friction experiments were conducted at room temperature (RT) and 400 °C with a Si3N4 ball as the counter body to comparatively study the effect of the oxidation temperature on the high-temperature friction behavior of the TO-treated Ti6Al4V alloy. The results show that the TO treatment can effectively improve the wear resistance of the samples at both room and high temperatures. Among them, the oxidation-treated samples at 700 °C show the best wear resistance, with a reduction of 92.6% at high temperatures; the amount of wear loss at room temperature was so small that it was almost incalculable. At room temperature, the friction surface formed uneven agglomerate formations, resulting in an elevated coefficient of friction (CoF) compared to the untreated samples. At a high temperature, however, the CoF is reduced compared to the untreated samples due to the formation of a homogeneous transfer film in the wear area that is caused by the interaction of Si3N4 and oxygen.

Synthesis and application of silicone-modified polyurethane as a slip-elastic finishing agent for polyamide fabrics

Despite the wide application of polyamide in clothing and home textiles, its inherent stiffness hardly meets consumers' preference for a smooth and elastic hand feel. In this study, a new hydroxyl silane coupling agent (KHS), 1-(4-(4-(4-(trimethoxysilyl)butyl)piperazin-1-yl)-3-(3-(trimethoxysilyl)propoxy) propan-2-ol, was synthesized and used to prepare a series of silicone-modified polyurethane (KHS-PU). KHS-PU then was finished onto the polyamide fabric via a pad-dry-cure procedure. The finishing process was optimized using the Minitab software. The morphology and elemental distribution of KHS-PU finished polyamide fabric were characterized using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The hand evaluation tests demonstrated that KHS-PU not only significantly enhanced the fabric's smooth and elastic properties, specifically evidenced by a 23 % reduction in surface friction coefficient, a 13 % decrease in bending average stiffness, a 10 % reduction in compression work, and a 40 % increase in compression recovery rate, but also exhibited good wash durability. In addition, the thermal and mechanical properties of KHS-PU finished fabric were further investigated. This work provides a valuable contribution to the field of surface science and textile engineering, offering insights into advanced fabric finishing techniques.

Pavement Condition Management Coupled with Skid Management at the Network Level: A Multi-Choice Goal Programming Approach

Highways promote economic growth and social development. Traditionally, pavement management considers pavement conditions for maintenance and rehabilitation (M&amp;R) decision-making along with system constraints. One of the major tasks of highway agencies is to promote safety. Highway safety involves a complicated interaction of multiple factors. However, it is well established that there is a link between pavement surface friction and safety. Pavement surface characteristics affect the safety and comfort of passengers. Since the pavement management process considers only pavement physical conditions in M&amp;R decision-making, there is a need to include safety indicators in the process to promote both riding comfort and safety. This study aims to integrate the pavement surface friction, that is, the skid resistance, into traditional pavement management. An optimization model has been proposed based on multi-choice goal programming by systematically integrating skid resistance into pavement M&amp;R decision-making along with pavement conditions. Multi-choice goal programming allows setting interval aspirations rather than a fixed target. A case study has been conducted to demonstrate the usefulness of the proposed model in managing pavement conditions and pavement skids together. The case study considered five goals related to pavement conditions, skid states, and M&amp;R costs. Interaction among the goals is discussed in different scenarios. The case study also uses friction treatment with traditional pavement management treatments. The model can capture the interaction between pavement conditions and pavement skids and determine the program that best achieves the goals. The proposed method provides a simple approach to selecting a network-level M&amp;R program and obtaining insights into the management of conditions and skid together.

Enhancing Wear Resistance in Functionally Graded Metallic Components: Insights from Nanoindentation and Mechanical Analysis.

To manufacture metallic components with high wear resistance, treatments such as nitriding and carburising followed by quenching and tempering (NQT and CQT, respectively) are applied to various types of steel to increase the hardness (H) of the friction surface. However, the wear mechanism of the resulting functionally graded materials has not been fully understood. In this study, specimens of industrial 99.82% pure iron treated with NQT at 913 and 1033 K, and CQT at 1203 K, as well as hot-rolled sheets without heat treatment were examined by performing nanoindentation tests to measure changes in their H, reduced Young's moduli (Er), elastic deformation energies (We), and plastic deformation energies (Wp) along the depth direction. The relationship between Wp/We and the elastic strain resistance (H/Er) can be expressed for all specimens via the equation Wp/We = -1.0 + 0.16 (H/Er)-1. Furthermore, the obtained H/Er av measured at 5 µm intervals based on the specimen profile and wear volume has a good correlation depending to the sliding distance, as confirmed by the results of the ring-on-plate sliding tests conducted for the carbon-treated, nitrogen-treated, and hot-rolled specimens. This study provides a new approach, using H/Er parameters to identify the dominant factors affecting wear resistance at the initial stage of wear that may contribute to the development of wear-resistant materials.

Повышение износостойкости цилиндрических поверхностей трения комбинированной электромеханической обработкой

Processing technology and technological equipment for the formation of a wear-resistant surface layer by implanting materials based on tungsten carbide (WC), are viewed. The effect of implanted WC powder on the formation of gradient wear-resistant structures in the friction surface of carbon steel formed during the implementation of combined electromechanical processing (WRCEMP) technology, has been studied. Resulting from heat and pressure impact in the zone of plastic deformation, intensive austenization of steel occurs with dissolution of WC powder and subsequent formation of highly dispersed composite structures caused by the decomposition of undercooled tangstem-supersaturated austenite. Combined comparative friction and wear tests were carried out for structural steel 45 with a graded structure of a hardened surface and rather expensive and technologically- difficult to obtain modern wear-resistant coatings and materials. The issue of WRCEMP technology practical application used for the «axis of satellite – satellite» friction pair is viewed. An assessment of the durability increase of the «axis of satellite – satellite» interface during the implementation of the considered processing methods and innovative technology was taken. Recommendations for the use of combined electromechanical processing technology at machine-building enterprises as a highly effective way to ensure and improve the performance of machine parts at the stage of their manufacture are given.

Friction and wear performance of aluminum-based self-lubricating materials derived from the 3D printed graphite skeletons with different morphologies and orientations

Using selective laser sintering 3D printing, this study shapes graphite in sphere, flake, and fiber morphologies into skeletons with various orientations. These skeletons are then used to create graphite/aluminum alloy composite self-lubricating materials. The results show that graphite morphology and orientation greatly affect the friction and wear properties of these composites. Graphite fiber exhibits the worst friction and wear performance. Perpendicular flake graphite forms a uniform, continuous lubricating film with high thermal conductivity for heat dissipation, preventing severe wear. Spherical graphite modifies the friction surface, achieving the lowest friction coefficient (0.2 ± 0.02) and wear rate (6.64 ×10−4 mm3/Nm) due to protective film, filling, and ball bearing effects.