Influence of variable-depth groove texture on the friction and wear performance of GCr15–SiC friction pairs under water lubrication

Influence of variable-depth groove texture on the friction and wear performance of GCr15–SiC friction pairs under water lubrication | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Influence of variable-depth groove texture on the friction and wear performance of GCr15–SiC friction pairs under water lubrication Yusen Zhang, Wei Long, Yan Qiao, Puteng Gui, Yuting Yin, Haifeng Qian This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4788486/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Oct, 2024 Read the published version in Tribology Letters → Version 1 posted 7 You are reading this latest preprint version Abstract Surface texturing is an effective method for enhancing tribological properties through the dynamic pressure effect and secondary lubrication mechanism. This study developed and evaluated a variable groove profile texture that enhanced the bearing capacity, reduced the shear friction, and achieved effective water lubrication of a GCr15 ball–SiC disk friction pair interface. Based on a structural design analysis, the coefficient of friction, wear characteristics, and triboelectric voltages produced by different disk textures were evaluated in a series of experiments using scanning electron microscope images and energy dispersive spectrometer. The results indicated that a groove profile slanted downward towards the outside of the disk provided the best comprehensive antifriction and anti-wear performance under the considered low- and medium-speed conditions. This texture enhanced the radial conduction of lubricant through the groove via the dynamic pressure effect and collected and expelled the abrasive particles generated during friction via centrifugal and gravity forces, reducing the quantity of abrasive particles at the interface and decreasing the coefficient of friction. The elevated contact stress and localized heat generated at the edge of the groove texture stimulated iron migration and tribochemical reactions at the interface, forming a dense, wear-resistant lubricant film that decreased the wear on the ball and disk surfaces. Finally, the variable-depth groove texture boosted the surface charge density generated at the contact interface, increased the capability of the surface to adsorb the lubricating water film, and thereby enhanced the antifriction and anti-wear performance of the lubricated friction pair system. surface micro-texture Variable-depth groove Water lubrication Friction and wear Interfacial tribochemical reaction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction Approximately 30–50% of the energy input during the relative movement of mechanical components is dissipated through various forms of friction, and approximately 80% of component failures are attributed to friction-induced damage [ 1 , 2 ]. Therefore, enhancing the lubrication efficiency of friction pairs and minimizing friction, wear, and energy consumption can provide significant social and economic advantages [ 3 ]. Recently, surface micro-texture technology was demonstrated to effectively regulate the lubrication characteristics of mechanical component surfaces [ 4 – 6 ]. An appropriate surface texture not only stores the lubricating fluid and traps abrasive particles but also encourages non-uniform local contact of the lubricating fluid in the surface micropores during the relative motion of friction pairs, leading to elastic hydrodynamic lubrication. As a result, the high-pressure zone inside the liquid film can be regarded as a series of miniature hydrodynamic lubrication bearings. Therefore, effectively avoiding or reducing direct contact between friction pair materials can enhance lubrication to reduce friction while ensuring sufficient bearing capacity. Numerous researchers have extensively studied antifriction and anti-wear textures by examining the effects of characteristics such as texture shape and distribution [ 9 – 11 ], surface micro-texture geometry [ 12 – 14 ], and working conditions [ 15 , 16 ], and have analyzed and summarized the relevant laws governing the stable coefficient of friction, bearing capacity, maximum Hertzian contact stress, and wear rate for different lubricating media accordingly [ 17 , 18 ]. As the speed requirements and load capacity of a friction pair increase, the sliding or rolling of hard particles between their contact surfaces will cause material loss (especially for hard but brittle and flaking-prone sintered ceramic and non-metal materials that exhibit excellent thermal conductivity), exacerbate the alternating stresses on the material surface, and promote the formation and expansion of cracks. The degree of friction and wear on the surface of the friction pair can be reduced by providing three-dimensional micro-textures, which not only store the lubrication fluid in the depth direction but also effectively accommodate and collect the abrasive particles and chips generated at the interface. Existing studies on micro-texture parameters have predominantly focused on the design and optimization of different texture shapes such as bionic structures with equal depths [ 19 – 21 ], and have analyzed the friction- and wear-reducing effects of different surface textures to enhance the dynamic pressure effect. Critically, in-depth analyses of surface flow field characteristics have confirmed that a reasonably designed groove profile can realize a texture that not only improves the pressure field characteristics of the lubricant film in the interface but also effectively collects hard abrasive particles and chips from the interface via the velocity vector distribution characteristics of the internal flow field, thereby preventing abrasive wear at its source. This promotes the transition of the interface lubrication state to the boundary and fluid lubrication states, thereby reducing the friction and wear between friction pairs. This study subjected SiC disc specimens provided with different variable-depth groove textures to relative motion against a GCr-15 ball and evaluated the effects of the groove profile and operational conditions on the friction and wear properties of the interface under deionized water lubrication. First, a theoretical analysis was conducted to optimize the morphological parameters of the texture and groove profile through numerical calculations. Next, a rotary friction experiment was undertaken to experimentally verify the coefficient of friction, wear characteristics, and interface triboelectric properties of the optimized variable-depth groove texture and examine the influence of the load and rotation speed on the tribological properties of the friction pair. Finally, the friction and wear reduction mechanisms of the variable-depth groove texture were elucidated by combining the theoretical analysis with the experimental test results. The work presented in this paper provides theoretical and experimental support for the study of friction- and wear-reduction between metal and ceramic materials under water lubrication. 2 Structural design and optimization 2.1 Geometric model The basic texture evaluated in this study is illustrated schematically in Fig. 1 (b). This texture comprised 72 angled grooves, each set at 30° to the disc radius. The specific geometric parameters are detailed in Table 1 . Under disc rotation, these grooves create a convergence wedge at a specific angle. This wedge resists the extrusion of the lubricating fluid as it moves into the base of the texture from the disc surface to increase the kinetic energy loss of the flow and enhance the pressure transformation, ultimately increasing the load-bearing capacity of the lubricant film. Therefore, the groove texture primarily enhances the load-bearing capacity of the lubricant film via the hydrodynamic pressure effect, consequently reducing the friction. In addition, the decrease in pressure along the groove bottom from the inside to the outside of the disc promotes the collection and removal of particles and chips generated by wear. This functionality is directly affected by the groove profile, underscoring the critical importance of designing the groove geometry. Therefore, the effect of hydrodynamic pressure and efficiency of abrasive and chip removal can be improved by optimizing the texture design. Table 1 Geometric parameters of groove texture Parameter Variable Value Outer diameter (mm) 50 Inner diameter (mm) 15 Disk height (mm) 12 Distribution circle radius (mm) \({d_{\text{f}}}\) 25.8 Tilt angle (°) \(\alpha\) 30 Groove length (mm) \({L_1}\) 11.2 Groove width (mm) \({W_1}\) 0.12 Groove depth (µm) 30 Area ratio (%) \({S_{\text{p}}}\) 4.7 Based on the variables defined in Table 1 , the area occupancy of the proposed groove texture \({S_{\text{p}}}\) is given by: 2.2 Mathematical model 2.2.1 Governing equation A mathematical model of fluid lubrication when using an internally distributed film to lubricate a textured surface was established based on fluid lubrication theory. Because the texture depth considered in this study was much smaller than the film thickness, the influence of the surface roughness was ignored, allowing the governing equations to be described by the Reynolds equation for the extruded film. Furthermore, the following assumptions were made when deriving the mathematical model [ 2 ]: (1) The role of the volume force was ignored. (2) There was no relative sliding between the surfaces of the friction pair and lubricating fluid. (3) The pressure along the thickness of the lubricant film, density, and viscosity remained unchanged. (4) The lubricating medium was a Newtonian fluid, and the internal flow of the flow field was laminar. (5) There was no inertial force. The work performed by the surface texture primarily depends on the supporting pressure in the lubricant film, which is determined by the dynamic pressure and film extrusion effects. Therefore, the Reynolds equation describing the system can be simplified into the following two-dimensional form: $$\frac{\partial }{{\partial x}}\left( {{h^3}\frac{{\partial p}}{{\partial x}}} \right)+\frac{\partial }{{\partial y}}\left( {{h^3}\frac{{\partial p}}{{\partial y}}} \right)=6\omega \mu \frac{{\partial (h)}}{{\partial x}}+12\mu \frac{{\partial h}}{{\partial t}}$$ 2 where is the lubricant film thickness in µm, is the lubricant film pressure in Pa, \(\mu\) is lubricant hydrodynamic viscosity in Pa·s, \(\omega\) is the relative rotational speed of the specimen in m/s, and is the time in s. 2.2.2 Film thickness equation When relative movement occurs between the surfaces of the friction pair, the lubricant medium between the surfaces creates a liquid film and generates a hydrodynamic pressure effect that facilitates lubrication. For a non-textured plane, the film thickness equation is given by $$h(x,y) \equiv {h_0}$$ 3 where \({h_0}\) is the thickness of the lubricant film in µm. For a groove-textured surface, the film thickness equation given by $$h(x,y)=\left\{ \begin{gathered} {h_0}{\text{ }}(x,y) \in {\Omega _1} \hfill \\ {h_0}+{h_g}(x,y){\text{ }}(x,y) \in {\Omega _2} \hfill \\ \end{gathered} \right.$$ 4 where \({\Omega _1}\) is the non-textured region; \({\Omega _2}\) is the groove-textured region; and \({h_g}(x,y)\) is the texture depth, which is constant as \({h_g}(x,y)=h={\text{const}}\) for an equal depth texture, in which is the maximum depth of the groove, and varies within \(0 \leqslant {h_g}(x,y) \leqslant h\) along the groove profile for a variable depth texture. 2.2.3 Simulation conditions The groove profile of the texture was optimized in this study using numerical simulations. Note that as the disc specimen was subjected to a rotational period, the lubricant film pressure inside the texture was assumed to vary following the same rule. The simulation efficiency was improved and its accuracy ensured by taking 1/72 of the entire lubricant film area (i.e., a single groove) as the calculation model. The lubricant film inlet boundary was taken as the upper boundary of the model, the film exit boundary was taken as the lower boundary of the model, and the left and right sides of the segment were considered periodic symmetric boundaries. The smooth bottom surface of the machined groove was considered a fixed wall surface, and the sides of the groove were considered moving walls. When the lubrication system is operating stably, its load and speed are typically fixed and the internal flow pattern of the lubricant film is consistent. Therefore, the numerical simulation results will be steady-state solutions. In this paper, the renormalization group k–ε turbulence model was applied in the ANSYS FLUENT platform to numerically simulate the lubricant film flow field between the friction pair. The density of the liquid water lubricant was set to 988.2 kg /m 3 and its dynamic viscosity was set to 1.003×10 − 3 Pa·s; the density of the water vapor was set to 0.5542 kg/m 3 , its dynamic viscosity was set to 1.34×10 − 5 Pa·s, and its cavitation was represented using the Schnerr–Sauer model with a cavitation pressure of 3540 Pa. The ambient and inlet/outlet pressures of the lubricant film were both set to standard atmospheric pressure, and the working temperature was the ambient temperature, 293 K. Finally, the “Coupled” algorithm, which is suitable for the steady-state solution, was selected to model the pressure–velocity coupling. The residual difference of the calculation results was less than 10 − 6 . 2.3 Texture optimization 2.3.1 Aspect ratio optimization The aspect ratio of the surface texture grooves exerts a significant influence on the efficacy of the resulting lubrication [ 22 ]. Indeed, for any particular texture, there exists an optimal groove aspect ratio that achieves the best antifriction and anti-wear performance. This paper accordingly evaluated the effects of three different groove texture aspect ratios on the antifriction and anti-wear lubrication performance given the same area occupancy condition to identify the optimal aspect ratio achieving the maximum surface bearing capacity and best dynamic lubrication effect. The dimensional parameters of the three evaluated groove textures, defined in terms of their length-to-width aspect ratios, are presented in Table 2 . Table 2 Dimensions of the evaluated groove textures Texture \({W_1}\) (mm) \({L_1}\) (mm) \({d_{\text{f}}}\) (mm) Aspect ratio ( \({L_1}\) / \({W_1}\) ) L/W-134.4 0.10 13.44 25.80 134.4 L/W-93.3 0.12 11.20 28.80 93.3 L/W-68.6 0.14 9.60 28.80 68.6 Figure 2 (a) shows the pressure distribution cloud diagrams obtained when using the different groove textures at different rotational speeds. As the speed increased, the positive and negative pressure values resulting from the hydrodynamic pressure effect generated by the texture increased, with the high-pressure region concentrated near the inner ring of the disc and the low-pressure region concentrated near the outer ring. The area and magnitude of the high-pressure region were the largest and those of the low-pressure region were the smallest when the aspect ratio was 93.3. As shown in Figs. 2 (c) and (e), the surface bearing capacity of the L/W-93.3 texture was the largest and exhibited an approximately linear increase with increasing rotational speed. The coefficient of friction of the L/W-134.4 texture was greater than 0.2 regardless of the rotational speed owing to its large aspect ratio, which increased the spacing between adjacent grooves. This restricted the storage space available for the lubricant film and thereby limited its formation, preventing the effective separation of the friction pair surfaces and increasing the interface coefficient of friction. In contrast, the texture with a small aspect ratio (L/W-68.6) could accommodate a large quantity of lubricant but reduced the effect of secondary lubrication, preventing the lubricant in the non-textured region from being effectively supplemented. This caused local stress concentrations in the lubricant film, deteriorating the surface tribological properties to exhibit the largest coefficient of friction at every evaluated speed. Therefore, the optimal groove texture aspect ratio was identified as 93.3, which was adopted in the subsequent analyses and experiments. 2.3.2 Groove profile optimization The groove profile applied in the surface texture also significantly affects antifriction and anti-wear lubrication performance. Therefore, the optimal groove profile was determined by evaluating surfaces with the three different groove profile textures shown in Figs. 1 (i)–(iii): flat bottom groove texture (FBT), shallow inner and deep outer groove texture (SDT), and deep inner and shallow outer groove texture (DST). The geometric parameters of these profiles are detailed in Table 3 . Table 3 Geometric parameters of the evaluated groove profiles Surface profile Inner depth (µm) Outer depth (µm) Area occupancy rate (%) SDT 0 30 4.7 FBT 30 30 4.7 DST 30 0 4.7 The pressure distribution cloud diagrams obtained at different speeds for the textures with different groove profiles are shown in Fig. 2 (b), and the corresponding bearing capacities are shown in Fig. 2 (d). The hydrodynamic pressure effect of the FBT was the strongest and the area and magnitude of the high-pressure region in its inner ring were the largest regardless of speed. The hydrodynamic pressure effect produced by the SDT was weaker and the magnitude of its high-pressure region was smaller, slightly decreasing its bearing capacity compared to that of the FBT. Finally, the DST exhibited the weakest hydrodynamic pressure effect of all three profiles because its average groove depth was smaller than that of the FBT; thus, it also exhibited the lowest bearing capacity. As shown in Fig. 2 (f), the coefficients of friction for the FBT and SDT surfaces were basically the same, whereas that for the DST surface was slightly larger. Note that this analysis focused on the fluid state between friction pairs considering only the effect of hydrodynamic pressure and did not fully consider the influence of abrasive particles, chemical reactions, triboelectricity, or other factors on the friction performance. Therefore, the combined influence of these factors on the properties of friction pairs must be comprehensively considered through further experimental study to reveal the potential laws and mechanisms underlying the friction process and provide a scientific basis for designing improved surface textures. 3 Experimental means and methods The ball–disk friction pair illustrated in Fig. 3 (a) was evaluated in this study using the friction testing machine shown in Fig. 3 (b). In this device, the rotational speed of the upper disc was controlled by a motor while the ball below was splined to the oil pool and secured to a fixture that was connected to a loading device through a force sensor. The GCr15 friction test ball had a radius of 6 mm, the friction disc material was made of SiC, and deionized water was used as the lubricant. The textured discs evaluated in this study were all processed using an LM-20 laser marking machine to create the grooves; scanning electron microscope (SEM) images of the resulting textures are shown in Fig. 3 (c). Note that there were tiny burrs on both sides of the micro-textured area of each processed disc that were removed by polishing with P600 mesh sandpaper and subsequent cleaning with ultrasonic waves. Before the tests, energy dispersive X-ray spectroscopy (EDS) was used to determine the elemental composition of each specimen surface. As shown in Fig. 3 (d), the use of laser marking to create the groove texture increased the oxygen content on the surface, which is consistent with previous literature [ 23 ]; this small quantity of oxygen can promote the formation of a friction oxide film. Furthermore, a contact angle and surface tension tester were used to measure the surface wettability contact angle of the non-textured and groove-textured surfaces with the results shown in Fig. 3 (e). The wettability contact angle of the specimen surfaces decreased from 92.38° for the non-textured surface to 67.95°, 67.38°, and 78.10° for the SDT, FBT, and DST surfaces, respectively, indicating that the surfaces became increasingly hydrophilic, which is conducive to lubrication by the water film. The experiments were conducted under working loads of 20 and 40 N and clockwise rotational speeds of 600, 1200, and 1800 rpm. In each test, the applied load and speed were stabilized and continued for 5 min under a constant temperature of 25 ℃ before the measured torque was recorded. Each set of experiment parameters was evaluated three times and the average results are reported in this paper. After the experiment, the surface morphology of each disc specimen was characterized by SEM and the changes in its surface element contents were analyzed by EDS. 4 Results and discussion 4.1 Friction and wear properties Speed and load are critical operating parameters influencing the tribological properties of friction pairs. Comparing the lubrication properties of the different evaluated textures at rotational speeds of 600, 1200, and 1800 rpm under different loads in Fig. 4 (a), the average coefficients of friction for the non-textured, SDT, and FBT surfaces consistently decreased with increasing rotational speed when the working load was 20 N. In contrast, the average coefficient of friction for the DST surface first increased to its maximum value at 1200 rpm, then decreased to its minimum value at 1800 rpm. The antifriction performance of the SDT surface was the best among the four specimens at 600 and 1200 rpm, when the average coefficients of friction were 0.091 and 0.059, respectively, representing 4.41- and 5.10-fold increases, respectively, over those for the non-textured surface at the same speeds. The FBT specimen exhibited the best antifriction performance at 1800 rpm with an average coefficient of friction of 0.038, representing a 2.18-fold increase over that for the non-textured surface at the same speed. As shown in Fig. 4 (c), when the load was 40 N, the average coefficient of friction for the non-textured surface increased with increasing rotational speed, whereas the average coefficients of friction for the SDT, FBT, and DST surfaces first increased, then decreased. The minimum average coefficients of friction for the SDT, FBT, and DST surfaces were observed at 600 rpm, 1800 rpm, and 1800 rpm, respectively. The SDT exhibited superior antifriction performance at low (600 rpm) and medium (1200 rpm) rotational speeds with average coefficients of friction of 0.021 and 0.043, respectively, representing 4.29- and 2.79-fold decreases, respectively, from those for the non-textured surface at the same speeds. Finally, the average coefficient of friction for the FBT specimen was 0.064 at 1800 rpm, representing a 2.03-fold decrease from that for the non-textured specimen at the same speed. These results indicate that the antifriction performance of the SDT texture was the best at low and medium speeds regardless of load, whereas the antifriction performance of the FBT texture was the best at high speeds. The following conclusions were obtained by combining the experimental observations with the numerical simulation results. At low and medium rotational speeds, the three-body wear caused by the abrasive particles produced by friction exerted the primary influence on the coefficient of friction. Under these working conditions, the small quantity of abrasive particles produced by friction were effectively adsorbed and discharged by the grooves. Note that the groove profile played a dominant role in the adsorption and discharge of the abrasive particles and chips produced by wear. The SDT surface was better than the FBT surface at collecting and discharging this wear debris owing to the “downward towards the outside” groove profile of the former, which allowed the collected debris to be moved away from the interface by the joint action of centrifugal and gravity forces. At a high rotational speed, the hydrodynamic pressure effect generated by the surface texture was the primary factor affecting friction performance owing to the enhanced kinetic energy of the fluid and more powerful dynamic pressure effect, which increased the bearing capacity of the water film. As a result, the hydrodynamic pressure effect of the FBT surface was superior than that of the SDT surface and the FBT surface exhibited the best antifriction performance accordingly. The wear condition of the friction pair is reflected by the morphology of the wear marks on the disc surface after grinding. As shown in Fig. 4 (b), under the 20 N working load, a minor pitting phenomenon was observed on the non-textured surface, the SDT and FBT surfaces exhibited relatively slight abrasive wear, and the DST surface exhibited extensive adhesive wear and a large quantity of abrasive chips accumulated in the grooves owing to the effect of secondary lubrication, leading to more severe three-body wear. This explains why the antifriction performance of the DST surface was worse than that of the FBT or SDT surfaces. As shown in Fig. 4 (d), the wear of the non-textured surface was more intense under the 40 N working load than under the 20 N working load, with relatively serious adhesive wear. This occurred because the rough peaks of the textured surface in contact with the ball in the initial stage of friction caused plastic deformation and shear to occur under the condition of relative sliding and high load, resulting in a high temperature that formed adhesive points mixed with surface contact. In the middle and later stages of the friction test, this mixed point and surface contact changed to purely surface contact, the Hertzian stress decreased gradually, and the adhesive wear gradually changed to abrasive wear. Furthermore, the wear of the SDT surface was smaller under the 40 N working load than under the 20 N working load, and fewer abrasive chips and particles were observed in its grooves than in those of the FBT and DST surfaces under the same load, highlighting the influence of the groove profile on the ability of the texture to radially conduct wear debris away from the interface. However, while the FBT surface collected more abrasive debris, the accumulation of a large quantity of this debris within the grooves eventually eliminated their collection effect and deteriorated the tribological properties of the surface. The DST surface exhibited serious adhesive wear and a large quantity of accumulated abrasive debris forming a structure similar to that achieved by cold welding. This occurred because the kinetic energy of the water film increased under the heavier load, causing the abrasive debris stored in the grooves to be channeled outward and upward into the interface, resulting in serious three-body wear. Further comparison of the FBT and SDT surface morphologies indicated substances sticking to both surfaces under the 40 N working load. This phenomenon was more obvious than under the 20 N working load because during the friction wear process, the abrasive debris was washed by the lubricant into the interface where a tribochemical reaction generated an oxide film protecting the surface under the higher load, avoiding the original surface friction observed under the lower load. The wear condition of the friction pair is also reflected by the wear rate and morphology of the GCr15 friction test ball. The wear rates of the test balls after griding with the non-textured and SDT surfaces under a 20 N working load are shown in Fig. 5 (a). The extent of ball wear after grinding with both surfaces decreased with increasing rotational speed, which is consistent with the trend observed for the coefficient of friction. Furthermore, the wear rates of the friction test ball when griding with the SDT surface at rotational speeds of 600, 1200, and 1800 rpm deceased by 39.18%, 30.07%, and 43.78%, respectively, compared to the corresponding wear rates when grinding with the non-textured surface. As shown in Fig. 5 (b), the surface of the friction test ball was rough after griding with the non-textured surface, exhibiting more patches and wider and deeper grooves than that after griding with the SDT surface, indicating more significant damage. Furthermore, spalling wear occurred under the action of contact stress, causing numerous wear fragments to flake from the substrate surface. These fragments acted as abrasive particles to deteriorate the tribological properties of the friction pair interface. As shown in Fig. 5 (c), the wear scars on the surface of the friction test ball after grinding with the SDT surface were smaller with fewer abrasive chips, explaining the lower wear rate observed. Based on this discussion and analysis, the SDT surface clearly exhibited strong comprehensive antifriction and anti-wear performance under low- and medium-speed conditions regardless of load. This can primarily be attributed to the excellent radial conduction ability realized by its “downward towards the outside” groove profile, which carried the abrasive debris away from the friction interface under the combined action of centrifugal and gravity forces. Simultaneously, an increase in the applied load facilitated the formation of a friction oxide film that helped to enhance lubrication performance. 4.2 Triboelectric properties Double electric layers and the electron-cloud potential well model are both relevant in liquid–solid sliding friction. During contact friction, the friction interface consistently resides in the deionizing lubricant pool such that when triboelectrification occurs between the solid and liquid, a contact charging phenomenon known as the friction voltage effect occurs [ 24 – 28 ]. This study employed an electrometer (Keithley 6514) to measure the voltage of the polarized electric field between the different ball–disk friction pairs under the 20 N working load. The principle underlying the triboelectric signal test is described in Fig. 6 (a). During friction between the GCr15 ball and SiC disc, the electron clouds of both materials overlap, transforming the symmetrical single-potential well of the previously individual atoms into an asymmetric double-potential well. This strong overlap of electron clouds reduces the potential barrier between the two atoms, causing their electrons to transition between them and producing a triboelectric effect that can be measured in terms of voltage. Furthermore, in the presence of water lubrication, the triboelectric effect also occurs between the deionized water, GCr15, and SiC, forming a double electric layer at the interface between the friction pair that creates a repulsive electric field. As shown in Figs. 6 (b) and (c), the triboelectric voltages on the non-textured and SDT surfaces exhibited decreasing periods and increasing peak values with increasing rotational speed. In addition, the periodic triboelectric voltages on the non-textured surface were more chaotic than those on the SDT surface owing to the more serious wear of the former. This occurred because the debris produced by wear diminished the surface charge density during the friction process, leading to increasingly uncertain and more prominently chaotic voltage fluctuations. As shown in Fig. 6 (d), the single-period peak triboelectric voltage on the non-textured surface decreased from 1.28 V to 0.59 V as the rotational speed increased from 600 rpm to 1800 rpm, which is consistent with the observed change in the coefficient of friction with rotational speed. This consistency is a result of the ability of the coefficient of friction to reflect the degree of contact between the two surfaces to a certain extent: the greater the coefficient of friction, the more intense the contact between the surfaces, and the greater the degree of electron cloud contact between the materials, the more electrons will transition and the greater the generated triboelectric voltage. In contrast, the single-period peak triboelectric voltage on the SDT surface was larger than that on the non-textured surface, and increased from 0.92 V to 1.26 V as the rotational speed increased from 600 rpm to 1800 rpm. This relationship is contrary to the observed change in the coefficient of friction with speed owing to the dynamic pressure effect produced by the groove texture machined on the disc surface, which enhanced the compression effect of the lubricant on the surface and thereby increased the strength of the polarized electric field. Simultaneously, the rotational speed increased the frequency of solid–liquid friction, elevating the triboelectric voltage, increasing the repulsion force between the two surfaces, thereby facilitating lubrication and reducing both friction and wear. In addition, the generated polarized electric field increased the adsorption capacity and stability of the lubricating water film during the friction process. This further reduced the contact degree at the interface between the friction pair materials, thereby reducing friction and wear. The observed triboelectric characteristics clearly demonstrated that two mutually repulsive polarized electric fields were generated by the sphere–disc friction pair during water-based lubrication that improved the lubrication mechanism associated with liquid–solid interface friction reduction. This occurred because the application of a texture to a smooth surface can effectively reduce the coefficient of friction and extent of wear. Specifically, during the friction process, a polarized electric field is formed on the surfaces of the two materials in the pair, generating a repulsive force between them that partially offsets the influence of the normal load and forms a stable lubricant film. This enhances the lubrication between the friction pair, leading to a simultaneous reduction in friction and wear. 4.3 Discussion of lubrication mechanism Based on the numerical simulations, experimental evaluations, and characterization analysis of the non-textured and SDT disc specimens before and after friction testing, the antifriction and anti-wear mechanisms of the variable-depth groove texture in the ball–disk friction pair can be inferred to primarily comprise the following aspects. First, as shown in Fig. 7 (a), the groove texture machined on the smooth surface not only effectively collected the abrasive debris generated during the friction process, induced a dynamic pressure effect, and provided support against the normal force, but also transported the debris away from the interface via the “downward towards the outside” radial groove profile. Indeed, as shown in Fig. 7 (b), a large quantity of abrasive debris was observed on the non-textured surface, and after friction compaction, some of this debris formed a relatively loose oxide film that provided limited surface protection. In contrast, most of the abrasive debris collected on the SDT surface were directly discharged through the grooves while a small remainder were transformed into a dense oxide film at the edges of the texture that more effectively protected the surface. Second, as shown in Fig. 7 (c), the oxide film generated on the textured surface during the friction process was denser and more wear-resistant than the original surface it replaced, reducing both friction and wear. As shown in Fig. 7 (d), the EDS analyses of the non-textured and SDT surfaces after friction indicated that the iron content was higher on the SDT surface than on the non-textured surface under the 20 N working load. This occurred because more iron was transferred to the SiC specimen surface by the GCr15 friction test ball by the considerable contact stress and local caloric value at the edge of the SDT texture. In the presence of deionized water and air, this iron formed an oxide film under influence of the friction heat in the contact area; after adsorption and compaction, friction occurred on this film instead of on the original surface, reducing the losses caused by friction and wear. When the working load was increased to 40 N, the EDS results indicated that the iron contents of the non-textured and SDT surfaces were 4.1 times and 2.7 times higher, respectively, than the corresponding iron contents under the 20 N working load. In this case, the greater iron content of the non-textured surface indicates that the high load promoted more tribochemical reactions between iron and oxygen. Simultaneously, the cycles of oxide film generation, adsorption, and compaction were reduced. However, under high-load conditions, the film formed on the non-textured surface was relatively loose such that it was constantly in the process of formation, fragmentation, regeneration, and re-fragmentation; therefore, a large quantity of secondary debris from the oxide film was formed on the surface that resulted in serious friction loss at the interface. In contrast, the oxide film formed at the edge of the SDT was denser and more wear-resistant, making it difficult to destroy under high-load conditions and reducing surface wear accordingly. Finally, as shown in Fig. 7 (e), the presence of a variable-depth groove texture increased the polarized electric field intensity between the ball and disk friction pair under water-based lubrication. During the friction process, the surfaces of the GCr15 and SiC materials produced the same charge magnitudes with the same signs, forming a mutually repulsive polarized electric field. As shown in Fig. 7 (f), the single-period peak triboelectric voltage on the non-textured surface increased from 5.19 V to 5.79 V with increasing rotational speed and that on the SDT surface increased from 5.42 V to 5.82 V, a 2.37% larger increase. Furthermore, the average single-period triboelectric voltage on the non-textured surface increased from 0.74 V to 0.90 V with increasing rotational speed and that on the SDT surface increased from 0.86 V to 1.12 V, a 18.48% larger increase. This indicates that the hydrodynamic pressure effect generated by the variable-depth groove texture increased the strength of the extruded lubricant fluid at the friction pair interface as well as that of the polarized electric field. This enhanced electric field helped to form a more stable water lubricant film while the repulsion between the polarized electric fields further enhanced its normal load capacity. Overall, these mechanisms worked together to improve the lubrication performance of the ball–disk pair during contact friction. 5 Conclusion This study evaluated two types of variable-depth groove textures to evaluate the friction behaviors of a GCr15 ball–SiC disk friction pair. The tribological and lubricating properties were evaluated and a microscopic analysis of the pair surfaces was conducted. The following conclusions were obtained: (1) Under water lubrication, the variable-depth groove texture enhanced the collection and discharge of abrasive particles and chips and improved the tribological properties of the disk surface. At low and medium rotational speeds, the three-body wear caused by this abrasive debris was the primary factor affecting the tribological properties of the disk surface, and the groove profile played a dominant role in its adsorption and discharge. The “downward towards the outside” groove profiles of the SDT surface effectively promoted the rapid discharge of this abrasive debris, thereby improving the tribological properties of the interface between the friction pair. (2) The SDT surface exhibited a significantly smaller coefficient of friction compared to the non-textured surface, particularly under a heavy working load at low and medium speeds. Under a low working load, the average coefficients of friction for the SDT surface at medium and low speeds were 0.091 and 0.059, respectively, representing 4.41- and 5.10-fold reductions, respectively, compared to those of the non-textured surface under the same conditions. Under a high working load, the average coefficients of friction for the SDT surface at medium and low speeds were 0.021 and 0.043, respectively, representing 4.29- and 2.79-fold reductions, respectively, compared to those of the non-textured surface under the same conditions. (3) The combined effect of the frictionally generated oxide film and polarized electric field enhanced the antifriction and anti-wear performance of the variable-depth groove texture. During the friction process under water-based lubrication, the iron from the GCr15 friction test ball migrated to the surface of the SiC disc to create a durable wear-resistant oxide film that protected the disc surface and facilitated lubrication. In addition, the triboelectric voltage at the SDT friction pair interface exceeded that at the non-textured friction pair interface, and the corresponding polarized electric field boosted the repulsive force between the two materials, forming a stable water lubricant film that reduced the friction contact area and decreased friction and wear through improved lubrication. Declarations Competing interests The authors declare no competing interests. Funding This research was supported by Yunnan Fundamental Research Projects (grant NO.202301AS07), Yunnan Province Ten Thousand Talents Program/Youth Top-notch Talent Program (No. YNWR-QNBJ-2018-162). Author Contribution YZ and YQ performed the simulations, YZ, YQ, YY, HQ,and PG performed the experiments, YZ and HQ performed the data analysis, WL conceptualized the work, and supervised the experiments and their analysis. YZ and WL wrote and revised the manuscript. Acknowledgements This research was supported by Yunnan Fundamental Research Projects (grant NO.202301AS07), Yunnan Province Ten Thousand Talents Program/Youth Top-notch Talent Program (No. YNWR-QNBJ-2018-162). Data availability All data generated or analyzed during this study are included in this published article. References Holmberg K., Erdemir A.: Influence of tribology on global energy consumption, costs and emissions. Friction 5 (3), 263-284 (2017). https://doi.org/10.1007/s40544-017-0183-5 Wen S., Huang P., Tian Y.:Principles of Tribology. Tsinghua University Beijing (2018). Kato K.: Industrial tribology in the past and future. Tribol. Online 6 (1), 1-9 (2011). https://doi.org/10.2474/trol.6.1 Chang T., Guo Z., Yuan C.: Study on influence of koch snowflake surface texture on tribological performance for marine water-lubricated bearings. Tribol. Int. 129 , 29-37 (2019). https://doi.org/10.1016/j.triboint.2018.08.015 Ezhihnaran V., Vasa N,. Vijayaraghavan L.: Investigation on generation of laser assisted dimples on piston ring surface and influence of dimple parameters on friction. Surf. Coat. Tech. 335 , 314-326 (2018). https://doi.org/10.1016/j.surfcoat.2017.12.052 Guo Z., Yuan C., Yan X., et al.: 3D surface characterizations of wear particles generated from lubricated regular concave cylinder liners. Tribol. Lett. 55 (1), 131-142 (2014). https://doi.org/10.1007/s11249-014-0340-1 Zhao L., Zhang B., Liu Y., et al.: State of the Art for Improving Tribological Performance Based on of Surface Texturing Technology. Tribology 42 (1), 202-224 (2022). https://doi.org/10.16078/j.tribology.2020263 Wang Z., Ye R., Xiang J..: The performance of textured surface in friction reducing: A review. Tribol. Int. 177 , 108010(2023). https://doi.org/10.1016/J.TRIBOINT.2022.108010 Liu Q., Yuan H., Yang D., et al.: Aggregation of micron-particles in microfluidic texture of artificial joint to improve tribological properties. Tribol. Int. 193 , 109365 (2024). https://doi.org/10.1016/J.TRIBOINT.2024.109365 Profito F.J., Vladescu S.C., Reddyhoff T., et al.: Numerical and experimental investigation of textured journal bearings for friction reduction. Tribol. Int. 195 , 109643 (2024). https://doi.org/10.1016/J.TRIBOINT.2024.109643 Xie Z., Li J., Tian Y., et al.: Theoretical and experimental study on influences of surface texture on lubrication performance of a novel bearing. Tribol. Int. 193 , 109351 (2024). https://doi.org/10.1016/J.TRIBOINT.2024.109351 Arslan A., Masjuki H., Varman M., et al.: Effects of texture diameter and depth on the tribological performance of dlc coating under lubricated sliding condition. Appl. Surf. Sci. 356 (1), 1135-1149 (2015). https://doi.org/10.1016/j.apsusc.2015.08.194 Choi Y.; Lee J.: A study on the effects of surface dimple geometry on fretting fatigue performance. Int. J. Precis. Eng. Man. 14 (4), 707-713 (2015). https://doi.org/10.1007/s12541-015-0094-1 Schuh J.K., Ewoldt R.H.: Asymmetric surface textures decrease friction with newtonian fluids in full film lubricated sliding contact. Tribol. Int. 97 (1), 490-498 (2016). https://doi.org/10.1016/j.triboint.2016.01.016 Zhou Y., Zhu H., Tang W., et al.: Development of the theoretical model for the optimal design of surface texturing on cylinder liner. Tribol. Int. 52 , 1-6 (2012). https://doi.org/10.1016/j.triboint.2011.12.017 Tang M., Huang X., Yu J., et al.: The effect of textured surfaces with different roughness structures on the tribological properties of al alloy. J. Mater. Eng. Perform. 25 (10), 4115-4125(2016). https://doi.org/10.1007/s11665-016-2251-9 Wei, Y., Yan, H., Li, S. et al. Numerical and Experimental Study of a Sector-Shaped Surface Texture in Friction Reduction. Tribol. Lett. 72, 60 (2024). https://doi.org/10.1007/s11249-024-01863-3 Fu, J., Fan, L., He, Y. et al. The Influence of Stress Concentration Caused by Surface Dimples on Tribochemical Reaction of Solid Lubricants Encapsulated in Surface Dimples. Tribol. Lett. 71, 119 (2023). https://doi.org/10.1007/s11249-023-01792-7 Guo Q., Zheng L., Zhong Y., et al.: Numerical simulation of hydrodynamic lubrication performance for continuous groove-textured surface. Tribol. Int. 167 , 107411 (2022). https://doi.org/10.1016/J.TRIBOINT.2021.107411 Liang Y., Wang C., Wang W., et al.: Effect of composite bionic micro-texture on bearing lubrication and cavitation characteristics of slipper pair. J. Mar. Sci. Eng. 11(3) , 582 (2023). https://doi.org/10.3390/JMSE11030582 Yin H., Yang J., Gu Q.: Numerical study on the hydrodynamic lubrication performance improvement of bio-inspired peregrine falcon wing-shaped microtexture. Tribol. Int. 191 , 109049 (2024). https://doi.org/10.1016/J.TRIBOINT.2023.109049 Wolski, M., Woloszynski, T., Podsiadlo, P. et al. Local Directional Fractal Signature Method for Surface Texture Analysis. Tribol. Lett. 70, 15 (2022). https://doi.org/10.1007/s11249-021-01547-2 Amsellem W., Sarvestani H.Y., Pankov V., et al.: Deep precision machining of sic ceramics by picosecond laser ablation. Ceram. Int. 49(6) , 9592-9606 (2023). https://doi.org/10.1016/J.CERAMINT.2022.11.129 Cheng G., Zhang T., Fu X., et al.: A comprehensive review of advancements and challenges from solid-solid to liquid-solid triboelectric nanogenerators. Adv. Mater. Technol.-US 9(6) , 2301588 (2024). https://doi.org/10.1002/admt.202301588 Chi J., Liu C., Che L., et al.: Harvesting water‐evaporation‐induced electricity based on liquid–solid triboelectric nanogenerator. Adv. Sci. 9(17) , 1-8 (2022). https://doi.org/10.1002/advs.202201586 Zhang H., Chen Y., Deng Z., et al.: A high-output performance disc-shaped liquid-solid triboelectric nanogenerator for harvesting omnidirectional ultra-low-frequency natural vibration energy. Nano Energy 121 , 109243 (2024). https://doi.org/10.1016/J.NANOEN.2023.109243 Zhang H., Dai G., Luo Y., et al.: Space volume effect in tube liquid–solid triboelectric nanogenerator for output performance enhancement. ACS Energy Lett. 9(4) , 1431-1439(2024). https://doi.org/10.1021/acsenergylett.4c00072 Zhou Z., Qin H., Cui P., et al.: Enhancing the output of liquid-solid triboelectric nanogenerators through surface roughness optimization. ACS Appl. Mater. Interfaces 16(4) , 4763-4771(2024). https://doi.org/10.1021/acsami.3c16352 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 23 Oct, 2024 Read the published version in Tribology Letters → Version 1 posted Editorial decision: Revision requested 15 Sep, 2024 Reviews received at journal 12 Sep, 2024 Reviewers agreed at journal 10 Sep, 2024 Reviewers invited by journal 26 Jul, 2024 Editor assigned by journal 23 Jul, 2024 Submission checks completed at journal 23 Jul, 2024 First submitted to journal 23 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4788486","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":334170340,"identity":"f14e45d1-c47f-4a7e-88ba-8f7390b31cb9","order_by":0,"name":"Yusen Zhang","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yusen","middleName":"","lastName":"Zhang","suffix":""},{"id":334170341,"identity":"593dc999-570f-4d0a-aafa-fc7bd7f28d84","order_by":1,"name":"Wei Long","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAr0lEQVRIie3PMQrCQBCF4QkBq9GtFzzEdiIEvUqCoI2HmCWFV1gvYmUxIYWNmDaQKgjWmxsYOxth0lnMX8/H8AA07R/jhCJAhsaQnPgAsF/awGICyUjqzFEuFItb7Wm4NujGf3E4Coi9F96HV4erlFJ7vgiI4+L0RO5wTTxL5yLS9L5EfqDjXEra4kN4ArFtP27hHdpQlbIti+bQU+TN1piyioOEfJXQtHtN0zTtd294uT482AiAhQAAAABJRU5ErkJggg==","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Wei","middleName":"","lastName":"Long","suffix":""},{"id":334170343,"identity":"355bb997-dc6f-4350-89cd-554c18874412","order_by":2,"name":"Yan Qiao","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yan","middleName":"","lastName":"Qiao","suffix":""},{"id":334170346,"identity":"c65afaac-eb8e-4bc4-92c3-4997bb53b2a1","order_by":3,"name":"Puteng Gui","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Puteng","middleName":"","lastName":"Gui","suffix":""},{"id":334170347,"identity":"fede295f-5b84-4f4b-8eba-64e61c773ed0","order_by":4,"name":"Yuting Yin","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yuting","middleName":"","lastName":"Yin","suffix":""},{"id":334170348,"identity":"20347ee7-7cb9-491f-9b16-ae96bd00e0f5","order_by":5,"name":"Haifeng Qian","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Haifeng","middleName":"","lastName":"Qian","suffix":""}],"badges":[],"createdAt":"2024-07-23 11:46:31","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4788486/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4788486/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11249-024-01926-5","type":"published","date":"2024-10-23T15:56:57+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":63289575,"identity":"a59cfe24-1372-46d1-9aa5-a054e2c19396","added_by":"auto","created_at":"2024-08-26 14:05:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1651690,"visible":true,"origin":"","legend":"\u003cp\u003eDisc specimen details: (a) Non-textured disc specimen; (b) groove texture diagram and sections showing the (i) shallow inner and deep outer groove texture (SDT), (ii) flat bottom groove texture (FBT), and (iii) deep inner and shallow outer groove texture (DST) profiles; (c) groove-textured disc specimen\u003c/p\u003e","description":"","filename":"Fig1.Discspecimendetails.png","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/a69f12db2cd3aeb30bfc3f04.png"},{"id":63289581,"identity":"363d469d-c5c1-4c7e-b008-19b5c0f655c4","added_by":"auto","created_at":"2024-08-26 14:05:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3624015,"visible":true,"origin":"","legend":"\u003cp\u003eTexture optimization. (a) Pressure cloud maps of textured surfaces with different groove aspect ratios and (b) different groove profiles according to speed. (c) Bearing capacities of textured surfaces with different groove aspect ratios and (d) different groove profiles. (e) Coefficients of friction for textured surfaces with different groove aspect ratios and (f) different groove profiles.\u003c/p\u003e","description":"","filename":"Fig2.Textureoptimization.png","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/6a77685bf233f0491bd0881d.png"},{"id":63289578,"identity":"f24eb73c-b2d9-4a25-af7a-867d669ed2b2","added_by":"auto","created_at":"2024-08-26 14:05:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3178225,"visible":true,"origin":"","legend":"\u003cp\u003eWorking principle of friction testing machine and characterization test. (a) Schematic diagram of friction testing setup and (b) picture of friction testing machine. (c) Original SEM images of the SDT, FBT, and DST disc specimen surfaces. (d) Elemental compositions of the disc specimens. (e) Wetting contact angles of the different disc specimen surfaces.\u003c/p\u003e","description":"","filename":"Fig3.Workingprincipleoffrictiontestingmachineandcharacterizationtest.png","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/ef5500377189e1c230eacfe1.png"},{"id":63289579,"identity":"6ba83be5-bd5b-4f12-87fb-8cefd0c0b45c","added_by":"auto","created_at":"2024-08-26 14:05:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":7828706,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Average coefficient of friction and (b) wear morphology of each specimen surface under a 20 N working load. (c) Average coefficient of friction and (d) wear morphology of each specimen surface under a 40 N working load.\u003c/p\u003e","description":"","filename":"Fig4.Coefficientoffrictionandwearmorphology.png","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/13c53320efb4822c48e458a0.png"},{"id":63290470,"identity":"550fa644-0c03-4356-96e3-cb94b56a0aec","added_by":"auto","created_at":"2024-08-26 14:13:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2617629,"visible":true,"origin":"","legend":"\u003cp\u003eWear rate and surface wear morphologies of the friction test ball after grinding at different speeds with the non-textured and SDT surfaces under a 20 N working load. (a) Extent of surface wear on each friction test ball according to rotational speed. (b) Surface wear morphologies of friction test ball after grinding at different speeds with the non-textured surface and the (c) SDT surface.\u003c/p\u003e","description":"","filename":"Fig5.WearrateandsurfacewearmorphologiesofthefrictiontestballaftergrindingatdifferentspeedswiththenontexturedandSDTsurfacesundera20Nworkingload.png","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/61000ba50f143365bc560b69.png"},{"id":63289583,"identity":"65fc1298-75dd-4fa9-8312-2bcefb47136f","added_by":"auto","created_at":"2024-08-26 14:05:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1222026,"visible":true,"origin":"","legend":"\u003cp\u003eTriboelectric signal test. (a) Schematic diagram of triboelectric test. (b) Peak periodic triboelectric voltages for the non-textured surface. (c) Peak periodic triboelectric voltages for the SDT surface. (d) Comparison of single-period peak triboelectric voltages.\u003c/p\u003e","description":"","filename":"Fig6.Triboelectricsignaltest.png","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/009d92d4c50888e1a44b06d8.png"},{"id":63290471,"identity":"44c74b57-74a6-45f7-a425-830e251cb2b2","added_by":"auto","created_at":"2024-08-26 14:13:19","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2331087,"visible":true,"origin":"","legend":"\u003cp\u003eLubrication mechanism provided by the textured surface. (a) Collection and removal of abrasive debris from the SDT surface. (b) SEM images of the non-textured and SDT surfaces. (c) Protection provided by the frictionally generated oxide film. (d) EDS results for the non-textured and SDT surfaces after grinding under 20 N and 40 N working loads. (e) Polarized triboelectric field voltages for non-textured and SDT surfaces. (f) Comparison of single-period peak and average triboelectric voltages for the non-textured and SDT surfaces.\u003c/p\u003e","description":"","filename":"Fig7.Lubricationmechanismprovidedbythetexturedsurface..png","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/fb2d136a761aea6441871bd1.png"},{"id":67681614,"identity":"6aa1c144-c01a-4f00-a745-d93b9007db78","added_by":"auto","created_at":"2024-10-28 16:06:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":29200887,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4788486/v1/6a4ca865-fc27-4346-aea5-46a0d7efc61c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Influence of variable-depth groove texture on the friction and wear performance of GCr15–SiC friction pairs under water lubrication","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eApproximately 30\u0026ndash;50% of the energy input during the relative movement of mechanical components is dissipated through various forms of friction, and approximately 80% of component failures are attributed to friction-induced damage [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Therefore, enhancing the lubrication efficiency of friction pairs and minimizing friction, wear, and energy consumption can provide significant social and economic advantages [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Recently, surface micro-texture technology was demonstrated to effectively regulate the lubrication characteristics of mechanical component surfaces [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. An appropriate surface texture not only stores the lubricating fluid and traps abrasive particles but also encourages non-uniform local contact of the lubricating fluid in the surface micropores during the relative motion of friction pairs, leading to elastic hydrodynamic lubrication. As a result, the high-pressure zone inside the liquid film can be regarded as a series of miniature hydrodynamic lubrication bearings. Therefore, effectively avoiding or reducing direct contact between friction pair materials can enhance lubrication to reduce friction while ensuring sufficient bearing capacity.\u003c/p\u003e \u003cp\u003eNumerous researchers have extensively studied antifriction and anti-wear textures by examining the effects of characteristics such as texture shape and distribution [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], surface micro-texture geometry [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], and working conditions [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and have analyzed and summarized the relevant laws governing the stable coefficient of friction, bearing capacity, maximum Hertzian contact stress, and wear rate for different lubricating media accordingly [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. As the speed requirements and load capacity of a friction pair increase, the sliding or rolling of hard particles between their contact surfaces will cause material loss (especially for hard but brittle and flaking-prone sintered ceramic and non-metal materials that exhibit excellent thermal conductivity), exacerbate the alternating stresses on the material surface, and promote the formation and expansion of cracks. The degree of friction and wear on the surface of the friction pair can be reduced by providing three-dimensional micro-textures, which not only store the lubrication fluid in the depth direction but also effectively accommodate and collect the abrasive particles and chips generated at the interface. Existing studies on micro-texture parameters have predominantly focused on the design and optimization of different texture shapes such as bionic structures with equal depths [\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], and have analyzed the friction- and wear-reducing effects of different surface textures to enhance the dynamic pressure effect. Critically, in-depth analyses of surface flow field characteristics have confirmed that a reasonably designed groove profile can realize a texture that not only improves the pressure field characteristics of the lubricant film in the interface but also effectively collects hard abrasive particles and chips from the interface via the velocity vector distribution characteristics of the internal flow field, thereby preventing abrasive wear at its source. This promotes the transition of the interface lubrication state to the boundary and fluid lubrication states, thereby reducing the friction and wear between friction pairs.\u003c/p\u003e \u003cp\u003eThis study subjected SiC disc specimens provided with different variable-depth groove textures to relative motion against a GCr-15 ball and evaluated the effects of the groove profile and operational conditions on the friction and wear properties of the interface under deionized water lubrication. First, a theoretical analysis was conducted to optimize the morphological parameters of the texture and groove profile through numerical calculations. Next, a rotary friction experiment was undertaken to experimentally verify the coefficient of friction, wear characteristics, and interface triboelectric properties of the optimized variable-depth groove texture and examine the influence of the load and rotation speed on the tribological properties of the friction pair. Finally, the friction and wear reduction mechanisms of the variable-depth groove texture were elucidated by combining the theoretical analysis with the experimental test results. The work presented in this paper provides theoretical and experimental support for the study of friction- and wear-reduction between metal and ceramic materials under water lubrication.\u003c/p\u003e"},{"header":"2 Structural design and optimization","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Geometric model\u003c/h2\u003e\n \u003cp\u003eThe basic texture evaluated in this study is illustrated schematically in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(b). This texture comprised 72 angled grooves, each set at 30\u0026deg; to the disc radius. The specific geometric parameters are detailed in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. Under disc rotation, these grooves create a convergence wedge at a specific angle. This wedge resists the extrusion of the lubricating fluid as it moves into the base of the texture from the disc surface to increase the kinetic energy loss of the flow and enhance the pressure transformation, ultimately increasing the load-bearing capacity of the lubricant film. Therefore, the groove texture primarily enhances the load-bearing capacity of the lubricant film via the hydrodynamic pressure effect, consequently reducing the friction. In addition, the decrease in pressure along the groove bottom from the inside to the outside of the disc promotes the collection and removal of particles and chips generated by wear. This functionality is directly affected by the groove profile, underscoring the critical importance of designing the groove geometry. Therefore, the effect of hydrodynamic pressure and efficiency of abrasive and chip removal can be improved by optimizing the texture design.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eGeometric parameters of groove texture\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVariable\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eValue\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOuter diameter (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInner diameter (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDisk height (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDistribution circle radius (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({d_{\\text{f}}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTilt angle (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\alpha\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGroove length (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({L_1}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGroove width (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({W_1}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGroove depth (\u0026micro;m)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eArea ratio (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({S_{\\text{p}}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\"\u003eBased on the variables defined in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, the area occupancy of the proposed groove texture \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({S_{\\text{p}}}\\)\u003c/span\u003e\u003c/span\u003e is given by:\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"686\" height=\"116\"\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Mathematical model\u003c/h2\u003e\n \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.1 Governing equation\u003c/h2\u003e\n \u003cp\u003eA mathematical model of fluid lubrication when using an internally distributed film to lubricate a textured surface was established based on fluid lubrication theory. Because the texture depth considered in this study was much smaller than the film thickness, the influence of the surface roughness was ignored, allowing the governing equations to be described by the Reynolds equation for the extruded film. Furthermore, the following assumptions were made when deriving the mathematical model [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e]:\u003c/p\u003e\n \u003cp\u003e(1) The role of the volume force was ignored.\u003c/p\u003e\n \u003cp\u003e(2) There was no relative sliding between the surfaces of the friction pair and lubricating fluid.\u003c/p\u003e\n \u003cp\u003e(3) The pressure along the thickness of the lubricant film, density, and viscosity remained unchanged.\u003c/p\u003e\n \u003cp\u003e(4) The lubricating medium was a Newtonian fluid, and the internal flow of the flow field was laminar.\u003c/p\u003e\n \u003cp\u003e(5) There was no inertial force.\u003c/p\u003e\n \u003cp\u003eThe work performed by the surface texture primarily depends on the supporting pressure in the lubricant film, which is determined by the dynamic pressure and film extrusion effects. Therefore, the Reynolds equation describing the system can be simplified into the following two-dimensional form:\u003c/p\u003e\n \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$$\\frac{\\partial }{{\\partial x}}\\left( {{h^3}\\frac{{\\partial p}}{{\\partial x}}} \\right)+\\frac{\\partial }{{\\partial y}}\\left( {{h^3}\\frac{{\\partial p}}{{\\partial y}}} \\right)=6\\omega \\mu \\frac{{\\partial (h)}}{{\\partial x}}+12\\mu \\frac{{\\partial h}}{{\\partial t}}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere is the lubricant film thickness in \u0026micro;m, is the lubricant film pressure in Pa, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\mu\\)\u003c/span\u003e\u003c/span\u003e is lubricant hydrodynamic viscosity in Pa\u0026middot;s, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\omega\\)\u003c/span\u003e\u003c/span\u003e is the relative rotational speed of the specimen in m/s, and \u0026nbsp;is the time in s.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.2 Film thickness equation\u003c/h2\u003e\n \u003cp\u003eWhen relative movement occurs between the surfaces of the friction pair, the lubricant medium between the surfaces creates a liquid film and generates a hydrodynamic pressure effect that facilitates lubrication. For a non-textured plane, the film thickness equation is given by\u003c/p\u003e\n \u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e$$h(x,y) \\equiv {h_0}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({h_0}\\)\u003c/span\u003e\u003c/span\u003e is the thickness of the lubricant film in \u0026micro;m.\u003c/p\u003e\n \u003cp\u003eFor a groove-textured surface, the film thickness equation given by\u003c/p\u003e\n \u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e$$h(x,y)=\\left\\{ \\begin{gathered} {h_0}{\\text{ }}(x,y) \\in {\\Omega _1} \\hfill \\\\ {h_0}+{h_g}(x,y){\\text{ }}(x,y) \\in {\\Omega _2} \\hfill \\\\ \\end{gathered} \\right.$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\Omega _1}\\)\u003c/span\u003e\u003c/span\u003e is the non-textured region; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\Omega _2}\\)\u003c/span\u003e\u003c/span\u003e is the groove-textured region; and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({h_g}(x,y)\\)\u003c/span\u003e\u003c/span\u003e is the texture depth, which is constant as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({h_g}(x,y)=h={\\text{const}}\\)\u003c/span\u003e\u003c/span\u003e for an equal depth texture, in which is the maximum depth of the groove, and varies within \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(0 \\leqslant {h_g}(x,y) \\leqslant h\\)\u003c/span\u003e\u003c/span\u003e along the groove profile for a variable depth texture.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.3 Simulation conditions\u003c/h2\u003e\n \u003cp\u003eThe groove profile of the texture was optimized in this study using numerical simulations. Note that as the disc specimen was subjected to a rotational period, the lubricant film pressure inside the texture was assumed to vary following the same rule. The simulation efficiency was improved and its accuracy ensured by taking 1/72 of the entire lubricant film area (i.e., a single groove) as the calculation model. The lubricant film inlet boundary was taken as the upper boundary of the model, the film exit boundary was taken as the lower boundary of the model, and the left and right sides of the segment were considered periodic symmetric boundaries. The smooth bottom surface of the machined groove was considered a fixed wall surface, and the sides of the groove were considered moving walls.\u003c/p\u003e\n \u003cp\u003eWhen the lubrication system is operating stably, its load and speed are typically fixed and the internal flow pattern of the lubricant film is consistent. Therefore, the numerical simulation results will be steady-state solutions. In this paper, the renormalization group \u003cem\u003ek\u0026ndash;\u0026epsilon;\u003c/em\u003e turbulence model was applied in the ANSYS FLUENT platform to numerically simulate the lubricant film flow field between the friction pair. The density of the liquid water lubricant was set to 988.2 kg /m\u003csup\u003e3\u003c/sup\u003e and its dynamic viscosity was set to 1.003\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e Pa\u0026middot;s; the density of the water vapor was set to 0.5542 kg/m\u003csup\u003e3\u003c/sup\u003e, its dynamic viscosity was set to 1.34\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e Pa\u0026middot;s, and its cavitation was represented using the Schnerr\u0026ndash;Sauer model with a cavitation pressure of 3540 Pa. The ambient and inlet/outlet pressures of the lubricant film were both set to standard atmospheric pressure, and the working temperature was the ambient temperature, 293 K. Finally, the \u0026ldquo;Coupled\u0026rdquo; algorithm, which is suitable for the steady-state solution, was selected to model the pressure\u0026ndash;velocity coupling. The residual difference of the calculation results was less than 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Texture optimization\u003c/h2\u003e\n \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.1 Aspect ratio optimization\u003c/h2\u003e\n \u003cp\u003eThe aspect ratio of the surface texture grooves exerts a significant influence on the efficacy of the resulting lubrication [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. Indeed, for any particular texture, there exists an optimal groove aspect ratio that achieves the best antifriction and anti-wear performance. This paper accordingly evaluated the effects of three different groove texture aspect ratios on the antifriction and anti-wear lubrication performance given the same area occupancy condition to identify the optimal aspect ratio achieving the maximum surface bearing capacity and best dynamic lubrication effect. The dimensional parameters of the three evaluated groove textures, defined in terms of their length-to-width aspect ratios, are presented in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDimensions of the evaluated groove textures\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTexture\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({W_1}\\)\u003c/span\u003e\u003c/span\u003e (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({L_1}\\)\u003c/span\u003e\u003c/span\u003e (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({d_{\\text{f}}}\\)\u003c/span\u003e\u003c/span\u003e (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAspect ratio (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({L_1}\\)\u003c/span\u003e\u003c/span\u003e/\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({W_1}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eL/W-134.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e134.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eL/W-93.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e93.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eL/W-68.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e68.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a) shows the pressure distribution cloud diagrams obtained when using the different groove textures at different rotational speeds. As the speed increased, the positive and negative pressure values resulting from the hydrodynamic pressure effect generated by the texture increased, with the high-pressure region concentrated near the inner ring of the disc and the low-pressure region concentrated near the outer ring. The area and magnitude of the high-pressure region were the largest and those of the low-pressure region were the smallest when the aspect ratio was 93.3. As shown in Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(c) and (e), the surface bearing capacity of the L/W-93.3 texture was the largest and exhibited an approximately linear increase with increasing rotational speed. The coefficient of friction of the L/W-134.4 texture was greater than 0.2 regardless of the rotational speed owing to its large aspect ratio, which increased the spacing between adjacent grooves. This restricted the storage space available for the lubricant film and thereby limited its formation, preventing the effective separation of the friction pair surfaces and increasing the interface coefficient of friction. In contrast, the texture with a small aspect ratio (L/W-68.6) could accommodate a large quantity of lubricant but reduced the effect of secondary lubrication, preventing the lubricant in the non-textured region from being effectively supplemented. This caused local stress concentrations in the lubricant film, deteriorating the surface tribological properties to exhibit the largest coefficient of friction at every evaluated speed. Therefore, the optimal groove texture aspect ratio was identified as 93.3, which was adopted in the subsequent analyses and experiments.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.2 Groove profile optimization\u003c/h2\u003e\n \u003cp\u003eThe groove profile applied in the surface texture also significantly affects antifriction and anti-wear lubrication performance. Therefore, the optimal groove profile was determined by evaluating surfaces with the three different groove profile textures shown in Figs. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(i)\u0026ndash;(iii): flat bottom groove texture (FBT), shallow inner and deep outer groove texture (SDT), and deep inner and shallow outer groove texture (DST). The geometric parameters of these profiles are detailed in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eGeometric parameters of the evaluated groove profiles\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSurface profile\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eInner depth (\u0026micro;m)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOuter depth (\u0026micro;m)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eArea occupancy rate (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSDT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFBT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDST\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eThe pressure distribution cloud diagrams obtained at different speeds for the textures with different groove profiles are shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(b), and the corresponding bearing capacities are shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(d). The hydrodynamic pressure effect of the FBT was the strongest and the area and magnitude of the high-pressure region in its inner ring were the largest regardless of speed. The hydrodynamic pressure effect produced by the SDT was weaker and the magnitude of its high-pressure region was smaller, slightly decreasing its bearing capacity compared to that of the FBT. Finally, the DST exhibited the weakest hydrodynamic pressure effect of all three profiles because its average groove depth was smaller than that of the FBT; thus, it also exhibited the lowest bearing capacity. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(f), the coefficients of friction for the FBT and SDT surfaces were basically the same, whereas that for the DST surface was slightly larger. Note that this analysis focused on the fluid state between friction pairs considering only the effect of hydrodynamic pressure and did not fully consider the influence of abrasive particles, chemical reactions, triboelectricity, or other factors on the friction performance. Therefore, the combined influence of these factors on the properties of friction pairs must be comprehensively considered through further experimental study to reveal the potential laws and mechanisms underlying the friction process and provide a scientific basis for designing improved surface textures.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3 Experimental means and methods","content":"\u003cp\u003eThe ball\u0026ndash;disk friction pair illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) was evaluated in this study using the friction testing machine shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b). In this device, the rotational speed of the upper disc was controlled by a motor while the ball below was splined to the oil pool and secured to a fixture that was connected to a loading device through a force sensor. The GCr15 friction test ball had a radius of 6 mm, the friction disc material was made of SiC, and deionized water was used as the lubricant.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe textured discs evaluated in this study were all processed using an LM-20 laser marking machine to create the grooves; scanning electron microscope (SEM) images of the resulting textures are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c). Note that there were tiny burrs on both sides of the micro-textured area of each processed disc that were removed by polishing with P600 mesh sandpaper and subsequent cleaning with ultrasonic waves. Before the tests, energy dispersive X-ray spectroscopy (EDS) was used to determine the elemental composition of each specimen surface. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d), the use of laser marking to create the groove texture increased the oxygen content on the surface, which is consistent with previous literature [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]; this small quantity of oxygen can promote the formation of a friction oxide film. Furthermore, a contact angle and surface tension tester were used to measure the surface wettability contact angle of the non-textured and groove-textured surfaces with the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(e). The wettability contact angle of the specimen surfaces decreased from 92.38\u0026deg; for the non-textured surface to 67.95\u0026deg;, 67.38\u0026deg;, and 78.10\u0026deg; for the SDT, FBT, and DST surfaces, respectively, indicating that the surfaces became increasingly hydrophilic, which is conducive to lubrication by the water film.\u003c/p\u003e \u003cp\u003eThe experiments were conducted under working loads of 20 and 40 N and clockwise rotational speeds of 600, 1200, and 1800 rpm. In each test, the applied load and speed were stabilized and continued for 5 min under a constant temperature of 25 ℃ before the measured torque was recorded. Each set of experiment parameters was evaluated three times and the average results are reported in this paper. After the experiment, the surface morphology of each disc specimen was characterized by SEM and the changes in its surface element contents were analyzed by EDS.\u003c/p\u003e"},{"header":"4 Results and discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Friction and wear properties\u003c/h2\u003e \u003cp\u003eSpeed and load are critical operating parameters influencing the tribological properties of friction pairs. Comparing the lubrication properties of the different evaluated textures at rotational speeds of 600, 1200, and 1800 rpm under different loads in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a), the average coefficients of friction for the non-textured, SDT, and FBT surfaces consistently decreased with increasing rotational speed when the working load was 20 N. In contrast, the average coefficient of friction for the DST surface first increased to its maximum value at 1200 rpm, then decreased to its minimum value at 1800 rpm. The antifriction performance of the SDT surface was the best among the four specimens at 600 and 1200 rpm, when the average coefficients of friction were 0.091 and 0.059, respectively, representing 4.41- and 5.10-fold increases, respectively, over those for the non-textured surface at the same speeds. The FBT specimen exhibited the best antifriction performance at 1800 rpm with an average coefficient of friction of 0.038, representing a 2.18-fold increase over that for the non-textured surface at the same speed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c), when the load was 40 N, the average coefficient of friction for the non-textured surface increased with increasing rotational speed, whereas the average coefficients of friction for the SDT, FBT, and DST surfaces first increased, then decreased. The minimum average coefficients of friction for the SDT, FBT, and DST surfaces were observed at 600 rpm, 1800 rpm, and 1800 rpm, respectively. The SDT exhibited superior antifriction performance at low (600 rpm) and medium (1200 rpm) rotational speeds with average coefficients of friction of 0.021 and 0.043, respectively, representing 4.29- and 2.79-fold decreases, respectively, from those for the non-textured surface at the same speeds. Finally, the average coefficient of friction for the FBT specimen was 0.064 at 1800 rpm, representing a 2.03-fold decrease from that for the non-textured specimen at the same speed. These results indicate that the antifriction performance of the SDT texture was the best at low and medium speeds regardless of load, whereas the antifriction performance of the FBT texture was the best at high speeds.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe following conclusions were obtained by combining the experimental observations with the numerical simulation results. At low and medium rotational speeds, the three-body wear caused by the abrasive particles produced by friction exerted the primary influence on the coefficient of friction. Under these working conditions, the small quantity of abrasive particles produced by friction were effectively adsorbed and discharged by the grooves. Note that the groove profile played a dominant role in the adsorption and discharge of the abrasive particles and chips produced by wear. The SDT surface was better than the FBT surface at collecting and discharging this wear debris owing to the \u0026ldquo;downward towards the outside\u0026rdquo; groove profile of the former, which allowed the collected debris to be moved away from the interface by the joint action of centrifugal and gravity forces. At a high rotational speed, the hydrodynamic pressure effect generated by the surface texture was the primary factor affecting friction performance owing to the enhanced kinetic energy of the fluid and more powerful dynamic pressure effect, which increased the bearing capacity of the water film. As a result, the hydrodynamic pressure effect of the FBT surface was superior than that of the SDT surface and the FBT surface exhibited the best antifriction performance accordingly.\u003c/p\u003e \u003cp\u003eThe wear condition of the friction pair is reflected by the morphology of the wear marks on the disc surface after grinding. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b), under the 20 N working load, a minor pitting phenomenon was observed on the non-textured surface, the SDT and FBT surfaces exhibited relatively slight abrasive wear, and the DST surface exhibited extensive adhesive wear and a large quantity of abrasive chips accumulated in the grooves owing to the effect of secondary lubrication, leading to more severe three-body wear. This explains why the antifriction performance of the DST surface was worse than that of the FBT or SDT surfaces. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d), the wear of the non-textured surface was more intense under the 40 N working load than under the 20 N working load, with relatively serious adhesive wear. This occurred because the rough peaks of the textured surface in contact with the ball in the initial stage of friction caused plastic deformation and shear to occur under the condition of relative sliding and high load, resulting in a high temperature that formed adhesive points mixed with surface contact. In the middle and later stages of the friction test, this mixed point and surface contact changed to purely surface contact, the Hertzian stress decreased gradually, and the adhesive wear gradually changed to abrasive wear. Furthermore, the wear of the SDT surface was smaller under the 40 N working load than under the 20 N working load, and fewer abrasive chips and particles were observed in its grooves than in those of the FBT and DST surfaces under the same load, highlighting the influence of the groove profile on the ability of the texture to radially conduct wear debris away from the interface. However, while the FBT surface collected more abrasive debris, the accumulation of a large quantity of this debris within the grooves eventually eliminated their collection effect and deteriorated the tribological properties of the surface. The DST surface exhibited serious adhesive wear and a large quantity of accumulated abrasive debris forming a structure similar to that achieved by cold welding. This occurred because the kinetic energy of the water film increased under the heavier load, causing the abrasive debris stored in the grooves to be channeled outward and upward into the interface, resulting in serious three-body wear. Further comparison of the FBT and SDT surface morphologies indicated substances sticking to both surfaces under the 40 N working load. This phenomenon was more obvious than under the 20 N working load because during the friction wear process, the abrasive debris was washed by the lubricant into the interface where a tribochemical reaction generated an oxide film protecting the surface under the higher load, avoiding the original surface friction observed under the lower load.\u003c/p\u003e \u003cp\u003eThe wear condition of the friction pair is also reflected by the wear rate and morphology of the GCr15 friction test ball. The wear rates of the test balls after griding with the non-textured and SDT surfaces under a 20 N working load are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a). The extent of ball wear after grinding with both surfaces decreased with increasing rotational speed, which is consistent with the trend observed for the coefficient of friction. Furthermore, the wear rates of the friction test ball when griding with the SDT surface at rotational speeds of 600, 1200, and 1800 rpm deceased by 39.18%, 30.07%, and 43.78%, respectively, compared to the corresponding wear rates when grinding with the non-textured surface. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b), the surface of the friction test ball was rough after griding with the non-textured surface, exhibiting more patches and wider and deeper grooves than that after griding with the SDT surface, indicating more significant damage. Furthermore, spalling wear occurred under the action of contact stress, causing numerous wear fragments to flake from the substrate surface. These fragments acted as abrasive particles to deteriorate the tribological properties of the friction pair interface. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c), the wear scars on the surface of the friction test ball after grinding with the SDT surface were smaller with fewer abrasive chips, explaining the lower wear rate observed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on this discussion and analysis, the SDT surface clearly exhibited strong comprehensive antifriction and anti-wear performance under low- and medium-speed conditions regardless of load. This can primarily be attributed to the excellent radial conduction ability realized by its \u0026ldquo;downward towards the outside\u0026rdquo; groove profile, which carried the abrasive debris away from the friction interface under the combined action of centrifugal and gravity forces. Simultaneously, an increase in the applied load facilitated the formation of a friction oxide film that helped to enhance lubrication performance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Triboelectric properties\u003c/h2\u003e \u003cp\u003eDouble electric layers and the electron-cloud potential well model are both relevant in liquid\u0026ndash;solid sliding friction. During contact friction, the friction interface consistently resides in the deionizing lubricant pool such that when triboelectrification occurs between the solid and liquid, a contact charging phenomenon known as the friction voltage effect occurs [\u003cspan additionalcitationids=\"CR25 CR26 CR27\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study employed an electrometer (Keithley 6514) to measure the voltage of the polarized electric field between the different ball\u0026ndash;disk friction pairs under the 20 N working load. The principle underlying the triboelectric signal test is described in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a). During friction between the GCr15 ball and SiC disc, the electron clouds of both materials overlap, transforming the symmetrical single-potential well of the previously individual atoms into an asymmetric double-potential well. This strong overlap of electron clouds reduces the potential barrier between the two atoms, causing their electrons to transition between them and producing a triboelectric effect that can be measured in terms of voltage. Furthermore, in the presence of water lubrication, the triboelectric effect also occurs between the deionized water, GCr15, and SiC, forming a double electric layer at the interface between the friction pair that creates a repulsive electric field.\u003c/p\u003e \u003cp\u003eAs shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b) and (c), the triboelectric voltages on the non-textured and SDT surfaces exhibited decreasing periods and increasing peak values with increasing rotational speed. In addition, the periodic triboelectric voltages on the non-textured surface were more chaotic than those on the SDT surface owing to the more serious wear of the former. This occurred because the debris produced by wear diminished the surface charge density during the friction process, leading to increasingly uncertain and more prominently chaotic voltage fluctuations. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d), the single-period peak triboelectric voltage on the non-textured surface decreased from 1.28 V to 0.59 V as the rotational speed increased from 600 rpm to 1800 rpm, which is consistent with the observed change in the coefficient of friction with rotational speed. This consistency is a result of the ability of the coefficient of friction to reflect the degree of contact between the two surfaces to a certain extent: the greater the coefficient of friction, the more intense the contact between the surfaces, and the greater the degree of electron cloud contact between the materials, the more electrons will transition and the greater the generated triboelectric voltage. In contrast, the single-period peak triboelectric voltage on the SDT surface was larger than that on the non-textured surface, and increased from 0.92 V to 1.26 V as the rotational speed increased from 600 rpm to 1800 rpm. This relationship is contrary to the observed change in the coefficient of friction with speed owing to the dynamic pressure effect produced by the groove texture machined on the disc surface, which enhanced the compression effect of the lubricant on the surface and thereby increased the strength of the polarized electric field. Simultaneously, the rotational speed increased the frequency of solid\u0026ndash;liquid friction, elevating the triboelectric voltage, increasing the repulsion force between the two surfaces, thereby facilitating lubrication and reducing both friction and wear. In addition, the generated polarized electric field increased the adsorption capacity and stability of the lubricating water film during the friction process. This further reduced the contact degree at the interface between the friction pair materials, thereby reducing friction and wear.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe observed triboelectric characteristics clearly demonstrated that two mutually repulsive polarized electric fields were generated by the sphere\u0026ndash;disc friction pair during water-based lubrication that improved the lubrication mechanism associated with liquid\u0026ndash;solid interface friction reduction. This occurred because the application of a texture to a smooth surface can effectively reduce the coefficient of friction and extent of wear. Specifically, during the friction process, a polarized electric field is formed on the surfaces of the two materials in the pair, generating a repulsive force between them that partially offsets the influence of the normal load and forms a stable lubricant film. This enhances the lubrication between the friction pair, leading to a simultaneous reduction in friction and wear.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Discussion of lubrication mechanism\u003c/h2\u003e \u003cp\u003eBased on the numerical simulations, experimental evaluations, and characterization analysis of the non-textured and SDT disc specimens before and after friction testing, the antifriction and anti-wear mechanisms of the variable-depth groove texture in the ball\u0026ndash;disk friction pair can be inferred to primarily comprise the following aspects.\u003c/p\u003e \u003cp\u003eFirst, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a), the groove texture machined on the smooth surface not only effectively collected the abrasive debris generated during the friction process, induced a dynamic pressure effect, and provided support against the normal force, but also transported the debris away from the interface via the \u0026ldquo;downward towards the outside\u0026rdquo; radial groove profile. Indeed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b), a large quantity of abrasive debris was observed on the non-textured surface, and after friction compaction, some of this debris formed a relatively loose oxide film that provided limited surface protection. In contrast, most of the abrasive debris collected on the SDT surface were directly discharged through the grooves while a small remainder were transformed into a dense oxide film at the edges of the texture that more effectively protected the surface.\u003c/p\u003e \u003cp\u003eSecond, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c), the oxide film generated on the textured surface during the friction process was denser and more wear-resistant than the original surface it replaced, reducing both friction and wear. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(d), the EDS analyses of the non-textured and SDT surfaces after friction indicated that the iron content was higher on the SDT surface than on the non-textured surface under the 20 N working load. This occurred because more iron was transferred to the SiC specimen surface by the GCr15 friction test ball by the considerable contact stress and local caloric value at the edge of the SDT texture. In the presence of deionized water and air, this iron formed an oxide film under influence of the friction heat in the contact area; after adsorption and compaction, friction occurred on this film instead of on the original surface, reducing the losses caused by friction and wear. When the working load was increased to 40 N, the EDS results indicated that the iron contents of the non-textured and SDT surfaces were 4.1 times and 2.7 times higher, respectively, than the corresponding iron contents under the 20 N working load. In this case, the greater iron content of the non-textured surface indicates that the high load promoted more tribochemical reactions between iron and oxygen. Simultaneously, the cycles of oxide film generation, adsorption, and compaction were reduced. However, under high-load conditions, the film formed on the non-textured surface was relatively loose such that it was constantly in the process of formation, fragmentation, regeneration, and re-fragmentation; therefore, a large quantity of secondary debris from the oxide film was formed on the surface that resulted in serious friction loss at the interface. In contrast, the oxide film formed at the edge of the SDT was denser and more wear-resistant, making it difficult to destroy under high-load conditions and reducing surface wear accordingly.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFinally, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(e), the presence of a variable-depth groove texture increased the polarized electric field intensity between the ball and disk friction pair under water-based lubrication. During the friction process, the surfaces of the GCr15 and SiC materials produced the same charge magnitudes with the same signs, forming a mutually repulsive polarized electric field. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(f), the single-period peak triboelectric voltage on the non-textured surface increased from 5.19 V to 5.79 V with increasing rotational speed and that on the SDT surface increased from 5.42 V to 5.82 V, a 2.37% larger increase. Furthermore, the average single-period triboelectric voltage on the non-textured surface increased from 0.74 V to 0.90 V with increasing rotational speed and that on the SDT surface increased from 0.86 V to 1.12 V, a 18.48% larger increase. This indicates that the hydrodynamic pressure effect generated by the variable-depth groove texture increased the strength of the extruded lubricant fluid at the friction pair interface as well as that of the polarized electric field. This enhanced electric field helped to form a more stable water lubricant film while the repulsion between the polarized electric fields further enhanced its normal load capacity. Overall, these mechanisms worked together to improve the lubrication performance of the ball\u0026ndash;disk pair during contact friction.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eThis study evaluated two types of variable-depth groove textures to evaluate the friction behaviors of a GCr15 ball\u0026ndash;SiC disk friction pair. The tribological and lubricating properties were evaluated and a microscopic analysis of the pair surfaces was conducted. The following conclusions were obtained:\u003c/p\u003e \u003cp\u003e(1) Under water lubrication, the variable-depth groove texture enhanced the collection and discharge of abrasive particles and chips and improved the tribological properties of the disk surface. At low and medium rotational speeds, the three-body wear caused by this abrasive debris was the primary factor affecting the tribological properties of the disk surface, and the groove profile played a dominant role in its adsorption and discharge. The \u0026ldquo;downward towards the outside\u0026rdquo; groove profiles of the SDT surface effectively promoted the rapid discharge of this abrasive debris, thereby improving the tribological properties of the interface between the friction pair.\u003c/p\u003e \u003cp\u003e(2) The SDT surface exhibited a significantly smaller coefficient of friction compared to the non-textured surface, particularly under a heavy working load at low and medium speeds. Under a low working load, the average coefficients of friction for the SDT surface at medium and low speeds were 0.091 and 0.059, respectively, representing 4.41- and 5.10-fold reductions, respectively, compared to those of the non-textured surface under the same conditions. Under a high working load, the average coefficients of friction for the SDT surface at medium and low speeds were 0.021 and 0.043, respectively, representing 4.29- and 2.79-fold reductions, respectively, compared to those of the non-textured surface under the same conditions.\u003c/p\u003e \u003cp\u003e(3) The combined effect of the frictionally generated oxide film and polarized electric field enhanced the antifriction and anti-wear performance of the variable-depth groove texture. During the friction process under water-based lubrication, the iron from the GCr15 friction test ball migrated to the surface of the SiC disc to create a durable wear-resistant oxide film that protected the disc surface and facilitated lubrication. In addition, the triboelectric voltage at the SDT friction pair interface exceeded that at the non-textured friction pair interface, and the corresponding polarized electric field boosted the repulsive force between the two materials, forming a stable water lubricant film that reduced the friction contact area and decreased friction and wear through improved lubrication.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research was supported by Yunnan Fundamental Research Projects (grant NO.202301AS07), Yunnan Province Ten Thousand Talents Program/Youth Top-notch Talent Program (No. YNWR-QNBJ-2018-162).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eYZ and YQ performed the simulations, YZ, YQ, YY, HQ,and PG performed the experiments, YZ and HQ performed the data analysis, WL conceptualized the work, and supervised the experiments and their analysis. YZ and WL wrote and revised the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis research was supported by Yunnan Fundamental Research Projects (grant NO.202301AS07), Yunnan Province Ten Thousand Talents Program/Youth Top-notch Talent Program (No. YNWR-QNBJ-2018-162).\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eAll data generated or analyzed during this study are included in this published article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHolmberg K., Erdemir A.: Influence of tribology on global energy consumption, costs and emissions. Friction \u003cstrong\u003e5\u003c/strong\u003e(3), 263-284 (2017). https://doi.org/10.1007/s40544-017-0183-5 \u003c/li\u003e\n\u003cli\u003eWen S., Huang P., Tian Y.:Principles of Tribology. Tsinghua University Beijing (2018).\u003c/li\u003e\n\u003cli\u003eKato K.: Industrial tribology in the past and future. Tribol. Online \u003cstrong\u003e6\u003c/strong\u003e(1), 1-9 (2011). https://doi.org/10.2474/trol.6.1 \u003c/li\u003e\n\u003cli\u003eChang T., Guo Z., Yuan C.: Study on influence of koch snowflake surface texture on tribological performance for marine water-lubricated bearings. Tribol. Int. \u003cstrong\u003e129\u003c/strong\u003e, 29-37 (2019). https://doi.org/10.1016/j.triboint.2018.08.015 \u003c/li\u003e\n\u003cli\u003eEzhihnaran V., Vasa N,. Vijayaraghavan L.: Investigation on generation of laser assisted dimples on piston ring surface and influence of dimple parameters on friction. Surf. Coat. Tech. \u003cstrong\u003e335\u003c/strong\u003e, 314-326 (2018). https://doi.org/10.1016/j.surfcoat.2017.12.052 \u003c/li\u003e\n\u003cli\u003eGuo Z., Yuan C., Yan X., et al.: 3D surface characterizations of wear particles generated from lubricated regular concave cylinder liners. Tribol. Lett. \u003cstrong\u003e55\u003c/strong\u003e(1), 131-142 (2014). https://doi.org/10.1007/s11249-014-0340-1 \u003c/li\u003e\n\u003cli\u003eZhao L., Zhang B., Liu Y., et al.: State of the Art for Improving Tribological Performance Based on of Surface Texturing Technology. Tribology \u003cstrong\u003e42\u003c/strong\u003e(1), 202-224 (2022). https://doi.org/10.16078/j.tribology.2020263 \u003c/li\u003e\n\u003cli\u003eWang Z., Ye R., Xiang J..: The performance of textured surface in friction reducing: A review. Tribol. Int. \u003cstrong\u003e177\u003c/strong\u003e, 108010(2023). https://doi.org/10.1016/J.TRIBOINT.2022.108010 \u003c/li\u003e\n\u003cli\u003eLiu Q., Yuan H., Yang D., et al.: Aggregation of micron-particles in microfluidic texture of artificial joint to improve tribological properties. Tribol. Int. \u003cstrong\u003e193\u003c/strong\u003e, 109365 (2024). https://doi.org/10.1016/J.TRIBOINT.2024.109365 \u003c/li\u003e\n\u003cli\u003eProfito F.J., Vladescu S.C., Reddyhoff T., et al.: Numerical and experimental investigation of textured journal bearings for friction reduction. Tribol. Int. \u003cstrong\u003e195\u003c/strong\u003e, 109643 (2024). https://doi.org/10.1016/J.TRIBOINT.2024.109643 \u003c/li\u003e\n\u003cli\u003eXie Z., Li J., Tian Y., et al.: Theoretical and experimental study on influences of surface texture on lubrication performance of a novel bearing. Tribol. Int. \u003cstrong\u003e193\u003c/strong\u003e, 109351 (2024). https://doi.org/10.1016/J.TRIBOINT.2024.109351 \u003c/li\u003e\n\u003cli\u003eArslan A., Masjuki H., Varman M., et al.: Effects of texture diameter and depth on the tribological performance of dlc coating under lubricated sliding condition. Appl. Surf. Sci. \u003cstrong\u003e356\u003c/strong\u003e(1), 1135-1149 (2015). https://doi.org/10.1016/j.apsusc.2015.08.194 \u003c/li\u003e\n\u003cli\u003eChoi Y.; Lee J.: A study on the effects of surface dimple geometry on fretting fatigue performance. Int. J. Precis. Eng. Man. \u003cstrong\u003e14\u003c/strong\u003e (4), 707-713 (2015). https://doi.org/10.1007/s12541-015-0094-1 \u003c/li\u003e\n\u003cli\u003eSchuh J.K., Ewoldt R.H.: Asymmetric surface textures decrease friction with newtonian fluids in full film lubricated sliding contact. Tribol. Int. \u003cstrong\u003e97 \u003c/strong\u003e(1), 490-498 (2016). https://doi.org/10.1016/j.triboint.2016.01.016 \u003c/li\u003e\n\u003cli\u003eZhou Y., Zhu H., Tang W., et al.: Development of the theoretical model for the optimal design of surface texturing on cylinder liner. Tribol. Int. \u003cstrong\u003e52\u003c/strong\u003e, 1-6 (2012). https://doi.org/10.1016/j.triboint.2011.12.017 \u003c/li\u003e\n\u003cli\u003eTang M., Huang X., Yu J., et al.: The effect of textured surfaces with different roughness structures on the tribological properties of al alloy. J. Mater. Eng. Perform. \u003cstrong\u003e25 (10),\u003c/strong\u003e 4115-4125(2016). https://doi.org/10.1007/s11665-016-2251-9 \u003c/li\u003e\n\u003cli\u003eWei, Y., Yan, H., Li, S. et al. Numerical and Experimental Study of a Sector-Shaped Surface Texture in Friction Reduction. Tribol. Lett. 72, 60 (2024). https://doi.org/10.1007/s11249-024-01863-3 \u003c/li\u003e\n\u003cli\u003eFu, J., Fan, L., He, Y. et al. The Influence of Stress Concentration Caused by Surface Dimples on Tribochemical Reaction of Solid Lubricants Encapsulated in Surface Dimples. Tribol. Lett. 71, 119 (2023). https://doi.org/10.1007/s11249-023-01792-7 \u003c/li\u003e\n\u003cli\u003eGuo Q., Zheng L., Zhong Y., et al.: Numerical simulation of hydrodynamic lubrication performance for continuous groove-textured surface. Tribol. Int. \u003cstrong\u003e167\u003c/strong\u003e, 107411 (2022). https://doi.org/10.1016/J.TRIBOINT.2021.107411\u003c/li\u003e\n\u003cli\u003eLiang Y., Wang C., Wang W., et al.: Effect of composite bionic micro-texture on bearing lubrication and cavitation characteristics of slipper pair. J. Mar. Sci. Eng. \u003cstrong\u003e11(3)\u003c/strong\u003e, 582 (2023). https://doi.org/10.3390/JMSE11030582 \u003c/li\u003e\n\u003cli\u003eYin H., Yang J., Gu Q.: Numerical study on the hydrodynamic lubrication performance improvement of bio-inspired peregrine falcon wing-shaped microtexture. Tribol. Int. \u003cstrong\u003e191\u003c/strong\u003e, 109049 (2024). https://doi.org/10.1016/J.TRIBOINT.2023.109049 \u003c/li\u003e\n\u003cli\u003eWolski, M., Woloszynski, T., Podsiadlo, P. et al. Local Directional Fractal Signature Method for Surface Texture Analysis. Tribol. Lett. 70, 15 (2022). https://doi.org/10.1007/s11249-021-01547-2 \u003c/li\u003e\n\u003cli\u003eAmsellem W., Sarvestani H.Y., Pankov V., et al.: Deep precision machining of sic ceramics by picosecond laser ablation. Ceram. Int. \u003cstrong\u003e49(6)\u003c/strong\u003e, 9592-9606 (2023). https://doi.org/10.1016/J.CERAMINT.2022.11.129 \u003c/li\u003e\n\u003cli\u003eCheng G., Zhang T., Fu X., et al.: A comprehensive review of advancements and challenges from solid-solid to liquid-solid triboelectric nanogenerators. Adv. Mater. Technol.-US \u003cstrong\u003e9(6)\u003c/strong\u003e, 2301588 (2024). https://doi.org/10.1002/admt.202301588 \u003c/li\u003e\n\u003cli\u003eChi J., Liu C., Che L., et al.: Harvesting water‐evaporation‐induced electricity based on liquid\u0026ndash;solid triboelectric nanogenerator. Adv. Sci. \u003cstrong\u003e9(17)\u003c/strong\u003e, 1-8 (2022). https://doi.org/10.1002/advs.202201586 \u003c/li\u003e\n\u003cli\u003eZhang H., Chen Y., Deng Z., et al.: A high-output performance disc-shaped liquid-solid triboelectric nanogenerator for harvesting omnidirectional ultra-low-frequency natural vibration energy. Nano Energy \u003cstrong\u003e121\u003c/strong\u003e, 109243 (2024). https://doi.org/10.1016/J.NANOEN.2023.109243 \u003c/li\u003e\n\u003cli\u003eZhang H., Dai G., Luo Y., et al.: Space volume effect in tube liquid\u0026ndash;solid triboelectric nanogenerator for output performance enhancement. ACS Energy Lett. \u003cstrong\u003e9(4)\u003c/strong\u003e, 1431-1439(2024). https://doi.org/10.1021/acsenergylett.4c00072 \u003c/li\u003e\n\u003cli\u003eZhou Z., Qin H., Cui P., et al.: Enhancing the output of liquid-solid triboelectric nanogenerators through surface roughness optimization. ACS Appl. Mater. Interfaces \u003cstrong\u003e16(4)\u003c/strong\u003e, 4763-4771(2024). https://doi.org/10.1021/acsami.3c16352 \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"tribology-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"tril","sideBox":"Learn more about [Tribology Letters](https://www.springer.com/journal/11249)","snPcode":"11249","submissionUrl":"https://submission.nature.com/new-submission/11249/3","title":"Tribology Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"surface micro-texture, Variable-depth groove, Water lubrication, Friction and wear, Interfacial tribochemical reaction","lastPublishedDoi":"10.21203/rs.3.rs-4788486/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4788486/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSurface texturing is an effective method for enhancing tribological properties through the dynamic pressure effect and secondary lubrication mechanism. This study developed and evaluated a variable groove profile texture that enhanced the bearing capacity, reduced the shear friction, and achieved effective water lubrication of a GCr15 ball\u0026ndash;SiC disk friction pair interface. Based on a structural design analysis, the coefficient of friction, wear characteristics, and triboelectric voltages produced by different disk textures were evaluated in a series of experiments using scanning electron microscope images and energy dispersive spectrometer. The results indicated that a groove profile slanted downward towards the outside of the disk provided the best comprehensive antifriction and anti-wear performance under the considered low- and medium-speed conditions. This texture enhanced the radial conduction of lubricant through the groove via the dynamic pressure effect and collected and expelled the abrasive particles generated during friction via centrifugal and gravity forces, reducing the quantity of abrasive particles at the interface and decreasing the coefficient of friction. The elevated contact stress and localized heat generated at the edge of the groove texture stimulated iron migration and tribochemical reactions at the interface, forming a dense, wear-resistant lubricant film that decreased the wear on the ball and disk surfaces. Finally, the variable-depth groove texture boosted the surface charge density generated at the contact interface, increased the capability of the surface to adsorb the lubricating water film, and thereby enhanced the antifriction and anti-wear performance of the lubricated friction pair system.\u003c/p\u003e","manuscriptTitle":"Influence of variable-depth groove texture on the friction and wear performance of GCr15–SiC friction pairs under water lubrication","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-26 14:05:14","doi":"10.21203/rs.3.rs-4788486/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-09-16T03:33:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-12T13:58:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"105984601288716898223042253236449540954","date":"2024-09-10T16:46:27+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-26T09:55:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-24T03:00:25+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-24T02:59:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"Tribology Letters","date":"2024-07-23T11:44:55+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"tribology-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"tril","sideBox":"Learn more about [Tribology Letters](https://www.springer.com/journal/11249)","snPcode":"11249","submissionUrl":"https://submission.nature.com/new-submission/11249/3","title":"Tribology Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b25da746-9196-4787-bd4b-c2d8a0c60f10","owner":[],"postedDate":"August 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-10-28T15:58:44+00:00","versionOfRecord":{"articleIdentity":"rs-4788486","link":"https://doi.org/10.1007/s11249-024-01926-5","journal":{"identity":"tribology-letters","isVorOnly":false,"title":"Tribology Letters"},"publishedOn":"2024-10-23 15:56:57","publishedOnDateReadable":"October 23rd, 2024"},"versionCreatedAt":"2024-08-26 14:05:14","video":"","vorDoi":"10.1007/s11249-024-01926-5","vorDoiUrl":"https://doi.org/10.1007/s11249-024-01926-5","workflowStages":[]},"version":"v1","identity":"rs-4788486","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4788486","identity":"rs-4788486","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}