Journal Information
Vol. 9. Issue 2.
Pages 1759-1767 (March - April 2020)
Share
Share
Download PDF
More article options
Visits
...
Vol. 9. Issue 2.
Pages 1759-1767 (March - April 2020)
Original Article
DOI: 10.1016/j.jmrt.2019.12.007
Open Access
Friction characterization when combining laser surface texturing and graphite-based lubricants
Visits
...
D. Martinez Krahmera,b, A.J. Sánchez Egeac,d,
Corresponding author
antonio.egea@upc.edu

Corresponding author.
, D. Celentanod, V. Martynenkoa,b, M. Cruchagae
a Center for Research and Development in Mechanics, National Institute of Industrial Technology (INTI), Avenida General Paz 5445, 1650 Miguelete, Provincia de Buenos Aires, Argentina
b Faculty of Engineering, Universidad Nacional de Lomas de Zamora, Juan XXIII y Camino de Cintura, 1832 Buenos Aires, Argentina
c Department of Mechanical Engineering (EEBE), Universitat Politècnica de Catalunya, Av. Eduard Maristany, 16, 08019 Barcelona, Spain
d Department of Mechanical and Metallurgical Engineering, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Región Metropolitana, Chile
e Department of Mechanical Engineering, University of Santiago (USACH), Av. Bernardo O´Higgins 3363, Santiago, Chile
Article information
Abstract
Full Text
Bibliography
Download PDF
Statistics
Figures (9)
Show moreShow less
Tables (2)
Table 1. Percent of the chemical elements and the average size of the graphite embedded.
Table 2. Surface roughness metrics (Rt and Sm) of the specimens tested during the pin-on disc test.
Show moreShow less
Abstract

The present work analyzes the friction capabilities at room temperature of three types of lubricants (denoted as A, B and C) with a graphite concentration of 5%. To do that, the standard pin-on disc test is deployed to study the variation of the friction coefficient when combining these graphite-based lubricants with surfaces made by grinding and different laser surface textures. These lubricants are characterized by measuring the percent of the chemical elements, the average size of the graphite particles and the kinematic viscosity. The experiments show that the lubricant B combined with a higher density of LST presents the lowest friction coefficient of about 0.24. Additionally, assuming a hydrodynamic regime for the textured surfaces, the fluid dynamics simulations carried out as part of the study showed, in agreement with the experimental measurements, the lowest friction coefficient value for a textured surface with the highest dimple density. This seems to be associated to the combined effect of an increase of the hydrodynamic pressure with a weak vortex formation within the dimples, due to the low distortion of the streamlines which, ultimately, attenuates the friction coefficient between the surfaces.

Keywords:
Laser surface texturing
Graphite-based
Lubricant
Friction coefficient
Pin-On disc
Numerical approach
Full Text
1Introduction

Since the beginning of the 60s, laser technologies have been a hot-topic in the manufacturing field and much research have been published in different areas, such as cutting, drilling, welding, surface treatments, micromachining, engraving, folding, additive manufacturing and laser surface texturing [1,2]. The surface texture displays a major interest, not only in forging and stamping processes with the aim of reducing the friction coefficient and, thus, enhance the lifespan of the tool by decreasing its wear [3–5], but also in bearings to increase the thickness of the lubricant to minimize the friction coefficient [6–9]. In this sense, a large number of surface texture studies performed with a range of surface roughness and topologies by using different manufacturing technologies, e.g., polishing [10], laser [11,12], burnishing [13,14], among others, have been reported. According to Etsion [15], the Laser Surface Texture (LST) technology is the most used and versatile technique for surface treatment, since allows create a wide range of textured surface with different dimple geometries in a shorted period of time.

Focusing on the laser technology to obtain textured surfaces with micro-dimples distributed along the surface of interest, different surface geometries combined with dimples were studied to determine the influence on the surface damaging, as reported by Sugar et al. [12]. In particular, three type of surface geometries, e.g., flat, parabolic and spherical, were performed to evaluate the quality of the texture in terms of its dimensions, shape and surface damage, observing that it is affected mainly by the metal projections and the class of the textured surface. Additionally, the size and morphology of the dimples have been found to decrease the friction coefficient up to a 15% during a ring test [16]. Furthermore, the initial surface grooves strategy (linear or zigzag) has an influence on the tribological capabilities, as reported by Xing et al. [17] when using a ball-on disc test on textured surfaces performed with Nd YAG laser on a ceramic material. Consequently, they found that the textured surface with the lowest step size in a zigzag configuration showed the lowest wear rate, due to the small effective contact area which increases the debris entrapment. Similar experiments were carried out by Vlădescu et al. [18], although they utilized a wear equipment with reciprocating movement combined with lubricant. The studied sample presented parallel grooves with different dimensions, steps sizes and perpendicular dispositions to the machine movement. As a result, lowest wear value was achieved when the widest, deepest and biggest step size groove configuration was used. However, they concluded that the volume of the texture was the crucial parameter, as long as the contact area was not exceeded. Furthermore, Dunn et al. [19] stated that the static friction coefficient increases by using a specific LST, combining a pulsing wavelength of a laser fiber of 1064nm with different frequency strategies. The results showed that the static friction increased almost 4 times compared with that of a non-textured surface. Furthermore, Yang et al. [20] also investigated different textures morphologies where the dimples presented a circle, triangular, square or rectangular shapes, all of them with an equivalent effective volume. These experiments proved that the lowest friction values where found when circular dimples were used. Besides the fluid dynamic simulation exhibited that also the greatest pressure was found for the surface texture with circular dimples. Other studies focused on the density of textured surfaces and the depth of the dimples. For example, Wan et al. [21] analyzed the friction coefficients and the wear capabilities of textured discs with plasma-sprayed Cr and evaluated them with pin-on disc tests. Geiger et al. [22] analyzed the lifespan of textured punches coated with titanium nitride used to produce parts by cold reverse extrusion. In particular, the laser parameters were adjusted to obtain dimples of 10μm diameter by 1μm depth, avoiding in this way the perforation of the layer thickness of 2μm of TiN. An increase in duration of 183% was found for the punches with a texture density of 20% compared with the base line (same punch without being textured). Besides, Schneider et al. [23] studied circular dimples with a small depth (h<8μm), texture densities of 5–30%, velocities between 0.04 and 2m/s and different geometry patterns of the surface texture. They found that lower friction coefficients are addressed for a density of 10% with a hexagonal pattern distribution when using a temperature of 100°C and polyalphaolefin-base lubricant. Accordingly, computational methods were performed by Scaraggi et al. [24] with the objective to find the geometries and size of the dimples to reduce the vortex in the flow and, subsequently, to decrease the friction forces between surfaces. Bijani et al. [25] performed another simulation study to analyze the film thickness of lubricant in four different dimples geometries (depth of 5μm), several velocities within 0.15 and 0.75m/s and textured surface densities between 12 and 40%. They stated that for low velocities, both the volume of the cavity and the thickness of the film increase and, consequently, the friction coefficients decrease.

Following the aforementioned research lines, the present work focuses on the study of the friction behavior while subjecting samples to the pin-on disc test at room temperature with different surface texture configurations combined with three graphite-based lubricants diluted in water up to 5%. To this end, the surface topographies, chemical composition, particle size and rheological behavior of the lubricants are all characterized. Keeping into consideration the review of Gropper et al. [26], experimental and numerical analyses are carried out to investigate the friction coefficient according to the forging conditions, the lubricant characteristics and the type of surface texture. In this sense, it can be stated which configuration presents better friction capabilities and, consequently, ensures a longer lifespan of the forging tools by reducing the wear and fatigue failure. Finally, a numerical simulation approach with the finite element method is performed qualitatively to validate the experimental results and, also, to define the film thickness and hydrodynamic pressure when studying different LSTs.

2Methodology

The methodology of this work was divided in four subsections: properties of the graphite-based lubricants, LST characterization, pin-on disk test at room temperature and numerical approach of the lubricant behavior. This section describes the protocols, devices and facilities utilized to investigate the friction capabilities of this kind of lubricants at different LSTs.

2.1Properties of the graphite-based lubricants

Three different lubricants were used in the present work, i.e., lubricant A, B and C all with a graphite concentration of about 5%. This concentration of graphite is commonly used in warm and hot forging processes in Argentine forging companies that cooperate with INTI. The three lubricants had the graphite suspension in water as a dilute and the density was within the range of 1.10g/cm3 and 1.20g/cm3, similar to the value reported in a previous study [27]. In order to characterize the three lubricants and describe their main differences, the analysis encompasses their chemical composition, the size of the graphite particles and the rheological properties. A scanning electron microscope (FEI model: QUANTA 250 FEG, FEI) was utilized to measure the particle size embedded in the matrix for each lubricant. Also, the rheological properties were assessed with an oscillatory mode rheometer (Anton Paar Physica model: MCR301) for each lubricant to estimate the effective viscosity. Fig. 1 exhibits the viscosity of each lubricant at room temperature of about 5% of graphite diluted in water.

Fig. 1.

Viscosity of each graphite-based lubricant measured at room temperature and a graphite diluted in water up to 5%.

(0.14MB).

Additionally, a scanning electron microscope (Philips SEM 505, Philips) equipped with the energy-dispersive X-ray spectroscopy module (UTW-Sapphire, model: PV7760/79 ME) was used to study the chemical composition of the three graphite-based lubricants. In particular, a standardless quantification analysis was deployed for the quantitative results for the X-ray spectra. Accordingly, Table 1 quantifies the average grain size and the percent of weight of the chemical composition of each element.

Table 1.

Percent of the chemical elements and the average size of the graphite embedded.

Lubricant  C (%)  O (%)  Na (%)  Al (%)  Si (%)  Graphite size (μm) 
Lub A  71.94  17.58  2.67  0.20  7.59  10.55±4.21 
Lub B  75.88  15.09  2.15  0.64  6.59  1.93±0.99 
Lub C  78.82  14.29  1.47  0.30  4.76  8.30±4.12 
2.2Laser surface texture characterization

The textured surface was performed by using a fiber laser (Han’s laser model: YLP-H20) which emits a wavelength of 1064nm with a maximum average power of 20W, where the repetition frequency was adjustable from 20 to 200kHz. The laser beam was focused onto the surface using a 100mm focusing lens. The topography of the semispherical dimples assessed had 70μm of diameter and 40μm of depth with the laser configuration mentioned above. A hexagonal laser texture pattern was used according to a biomimetic concept with the Dung beetle [28]. Besides, three different textured surface densities were carried out: 11%, 31% and 50%, in order to analyze the corresponding friction coefficients in terms of the respective contact effective areas. According to Schneider el al. [23]. and Scaraggi et al. [24], common values of textured surface densities are within 5–40%. In this work, we decided to use two intermediate and one extreme values of textured densities, because these previous works did not combine texture surfaces with graphite-based lubricants, where solid particles are expected to fill the dimples and, thus, affect the friction coefficient. The distance between the center of the dimples for each configuration was 190μm, 148μm and 93μm for textured surface densities of 11%, 31% and 50%, respectively. Fig. 2 shows the cross sectional area of the dimple to evaluate edges or burrs around the crater, which can affect the friction coefficient. The cross section was achieved by electrical discharge machining to analyze the quality of the dimple morphology. All the dimples exhibited a spherical shape with an irregular surface. Although, some rims/edges were also found in the crater, the size of the rims/edges were small enough (below the initial average surface roughness of the disc) to not affect the friction coefficients during the pin-on disc test. Note that after the laser texturing, a manual polishing with brusher and a paper sand of 1200 grit were used to remove the rims and later 5min of ultrasound vibration (J.P. Selecta S.A., model: 3000683) were used to smooth and to clean all the textured surfaces and dimples.

Fig. 2.

Cross sectional area of the dimples to analyze the dimples morphology and the edges or rim around the crater.

(0.17MB).
2.3Pin-on disc test at room temperature

Firstly, 20pin. of SAE 1045 steel were manufactured in a numerical control lathe Promecor model SMT 19/500. These pins presented a semispherical end of 4mm of diameter which were manually polished up to a paper sand of 1000 grit (grain size of 10.3μm). This semispherical geometry let us have an approach of the typical forged contact pressure with a small axial force, on the contrary a higher axial force is required if flat pin is used. Our machined pins presented a circular contact area of about 0.2mm in diameter and, consequently, for the used axial force the contact pressure is around 200MPa, which is within the forging range found by Abachi et al. [29]. At the same time, 20 discs of SAE H13 steel were manufactured in the same lathe machine with a geometry of 63mm of external diameter, 19mm of internal diameter and 6mm of thickness. These discs were hardened and tempered to a hardness of 51.8±1 HRC. Later, these discs were rectified in a flat tangential grinding machine with a fine abrasive tool (A46H10V - average grit size of 0.38mm). Finally, three different density of textured surfaces (11%, 31% and 50%) were performed in 9 discs that were previously rectified with a small abrasive tool. The surface textures were assessed in both faces of the disc, so a total of 18 textured surfaces were disposed. The force during the pin-on disc test was recorded with a data logger (Vernier, model LabQuest) with a load range of 50N. Besides, the rotational plate was connected to a servomotor which allows to vary the rotation speed within the range of 10–1000rpm. The surface roughness of the specimens was measured with a portable profilometer (Taylor Hobson, model: Surtronic 3+). Table 2 shows the maximum peak-valley surface roughness (Rt) and the mean spacing between profile peaks at the mean line (Sm) of the initial grinded surfaces. The roughness measurements were set with a cut-off and evaluation lengths of 0.8mm and 4mm, respectively.

Table 2.

Surface roughness metrics (Rt and Sm) of the specimens tested during the pin-on disc test.

Parameter  Parallel to grinding direction  Perpendicular to grinding direction 
Rt (μm)  5.40±1.76  6.56±0.64 
Sm (μm)  20.60±3.21  17.60±1.34 

Later, the disc and the pins were allocated in the pin-on disc machine to run the experiment. Subsequently, the diluted graphite-based lubricant was constantly added on the disc verifying the proper dispersion of the lubricant all over the specimen before running the test. The applied load of the tip over the disc was set at 6.5N and the tangential velocity at the contact region of the tip and disc was 0.2m/s (∼100rpm). These applied force and the tangential velocity come from previous simulation works to mimic the forging pressure and displacement velocities [29]. The pin-on disc test took about 20min to ensure that only the stationary scenario of the friction coefficient, found after 10min, was recorded. Finally, a total of 36 experiments were performed: firstly, 18 experiments were done using the grinded surface (base-line), 3 types of graphite-based lubricants and 6 repetitions per combination. Then, 18 experiments were performed to investigate the friction capabilities of 3 different texture densities and 6 repetitions per configuration using one graphite-based lubricant (the one for which the best performance was achieved from the previous analysis). A schematic illustration of the combination of different graphite-based lubricants and density of textured surfaces investigated in an in-house tribometer (pin-on disc test) manufactured at the INTI-Mechanics Center in Argentina is shown in Fig. 3.

Fig. 3.

Pin-on disc test schema combining three graphite-based lubricants and textured surface densities to analyze the friction coefficient at room temperature.

(0.38MB).
2.4Numerical approach

To qualitatively assess the influence of the dimple density on the friction coefficient, a 2D numerical simulation of the fluid dynamics response of the lubricant in a film (or channel) mimicking an idealized pin-on disc test was carried out. Cavitation phenomenon was not considered in this approach, due to its complexity and the lack of experimental validation. To this end, the steady-state Navier–Stokes equations of an incompressible laminar flow considering a strain-rate viscosity were solved in the context of the finite element method [30]. Thus, the friction coefficient μ can be estimated according to the Petroff approach as:

where Ff is the tangential viscous force and Fs is the normal pressure force, both per unit length at the upper wall of the channel. These forces can be computed as:
where ϑ(u) is the dynamic viscosity, L is the length of the channel wall along the horizontal coordinate x, u(x) is the sliding velocity, p(x) is the pressure and y is the vertical coordinate normal to the channel wall (note that for constant ϑ, ∂u/∂y and p, the classical expression μ=ϑu/hp is recovered, where h is the film height).

3Results

The results of the present work are divided in two subsections: experimental measurements and numerical predictions obtained via simulation. Firstly, the friction coefficient is study with the pin-on disc test at room temperature to compare the tribology capabilities of the three graphite-based lubricants and textured surfaces. Later, a numerical approach is carried out to predict the lubricant distribution depending on the lubricant viscosity, shear rate and percentage of surface density.

3.1Friction coefficient at room temperature

Friction coefficients are studied on the grinded surfaces by using the three lubricants in a pin-on disc test. Accordingly, Fig. 4a shows the trend of the friction coefficients during the duration (20min) of pin-on disc test for surfaces respectively. While, Fig. 4b present the corresponding box plots of both surfaces tested with the three lubricants at the stationary phase of the pin-on disc test (>10min).

Fig. 4.

Friction coefficients curves for the three lubricants (a) and the box plots at the stationary phase of the pin-on disc test (b).

(0.11MB).

Lubricant B exhibits the lower friction coefficient of about 0.43, while the friction coefficients for lubricant A and C are close to 0.45. These differences seem to be attributed to the viscosity and grain size of the graphite embedded in the matrix of the lubricant, which may affect the cavitation effect and, therefore, change the pressures between surfaces. Lubricant B presents the lowest viscosity and the graphite are about 4.0 times smaller in average than that of the other two lubricants, as we denoted in our previous experiments [31]. The smaller size of the particles of graphite favors the formation of a continuous and effective film thickness at the interfaces [32] and facilitates the filling of the dimples of the textured surfaces, helping to ensure continuity in the lubricant layer between surfaces in starved conditions [25]. Fig. 5 shows SEM images that were taken before and after the pin-on disc to analyze the interaction of the dimples and the graphite embedded in the lubricant.

Fig. 5.

SEM images of the LST density of 31% before a) and after b) the pin-on disc tested with lubricant type B.

(0.22MB).

As a consequence of these filled dimples, the cavitation will be affected and, consequently, the pressure build-up within the dimple will modified the friction coefficient [26]. In order to analyze the lubricant capabilities in different textured surfaces, additional pin-on disc tests were performed using only lubricant B (which showed the lowest friction performance) in three different LST densities of 11%, 31% and 50% and compared with respect to the grinded surface. Consequently, Fig. 6 shows the friction coefficient trends and the associated box plots at the stationary phase.

Fig. 6.

Friction coefficient trend (a) and box-plot at the stationary phase (b) of the three LSTs and the grinded surface when using lubricant B.

(0.18MB).

The LST with higher density presents lower values of friction coefficient, the average values are 0.34, 0.30 and 0.24 for textured surface with densities of 11%, 31% and 50%, respectively. Note, however, that more stable friction conditions are achieved for the grinded surface than for LST since the standard error is lower in the previous case. Therefore, high volume of dimples enhances the friction capabilities by reducing the friction coefficient. In this sense, dimples behave as a reservoir of lubricant that affect to the film thickness of the lubricant in the pin-on disc test and, consequently, affect the sliding mechanism and friction between both interfaces, as reported by Etsion [15]. In order to understand why the friction coefficient decreases for textured surfaces with large density of dimples, firstly it is necessary to determine the type of regime: boundary, mixed or hydrodynamic. Accordingly, Fig. 7 exhibits the Stribeck curves when using lubricant B, 6.5N of axial load and a range of tangential velocities from 0.065 to 0.4m/s during the pin-on disc tests of the grinded surface and the 50% of LST, i.e., the worst and the best surface configurations in terms of the friction coefficient.

Fig. 7.

Friction behavior in the Stribeck curve for the grinded surface and the 50% of LST, low viscosity lubricant (lubricant B) and 6.5N of axial load.

(0.16MB).

The Stribeck curves show that minimum values of the friction coefficient are found for tangential velocity of about 0.2m/s (around 0.001 of Hersey parameter), independently of the studied surface configuration. Note that all the experiments performed in the previous sections were carried out with a tangential velocity of 0.2m/s, which was the best friction scenario based on the Stribeck curves. According to the literature [33], for a tangential velocity of 0.2m/s, axial force of 6.5N and low viscosity lubricant, the regime of the lubricant for the grinded surface (base-line) is at the frontier between the mixed and hydrodynamic lubrications, which is also called the elasto-hydrodynamic lubrication [31]. Whereas, the textured surface is allocated in the hydrodynamic lubrication for the same aforementioned conditions used during the pin-on disc tests. As the interest is to investigate the friction coefficient and the film thickness for different LST, as thoroughly studied by Etsion and coworkers [15,34], it is expected that for LST the Stribeck curve moves to the left and, consequently, a hydrodynamic lubrication is more likely to be found for the three textured surface conditions. In addition, based on the axial force and the sliding speed configuration used in the present work for a high textured surface density, a hydrodynamic lubrication can be also assumed by looking at the results presented by Kovalchenko et al. [33]. Accordingly, the numerical simulation is performed with a hydrodynamic lubrication regime to describe the film thickness, relative pressure of the lubricant at the dimples and the vortex formation in the center of the dimples. Then, the friction coefficient for textured surfaces with low and high density of dimples will be estimated to validate the experimental results recorded with the pin-on disc test with a tangential velocity of 0.2m/s.

3.2Numerical analysis of lubricant B in two laser textured surfaces (11% and 50%)

Due to the simple assumptions commented in Section 2.4, the numerical simulation carried out in this work is aimed at only comparatively describe the fluid dynamics response of the lubricant in the film between the cases analyzed. In this context, the numerical simulation is focused on the fluid dynamics responses of lubricant B with LST densities of dimples of 11% and 50%, both in a 560μm film length; see Fig. 8. The dimples are 40μm depth and have a diameter of 70μm. The film thickness of case 11% was chosen as 10μm [20] while the film thickness of case 50% was computed in order to obtain, as in the pin-on-disc experiment, the same normal pressure force as that of case 11% although the pressure distribution is, as can be appreciated in Fig. 9, different in both cases. Thus, the resulting film thickness of case TS50% was 15μm. The strain-rate dependent viscosity was considered according to the relationship shown in Fig. 1. A linear (along the film height) inlet velocity profile was assumed with a sliding velocity of 0.2m/s. A zero reference pressure value was imposed at the upper outlet corner of the channel. The dimensionless pressure and streamline contours for cases 11% and 50% are plotted in Fig. 8. Although these variables present similar patterns, the normal velocity gradients and consequently the tangential viscous forces differ for both cases due to their different film heights (in these cases, note that the vortex formation does not practically affect the main stream flow along the film). From these results, the ratio between the friction coefficients (computed with Eqs. (1) and (2) from the results of the numerical simulation) of cases 50% and 11% is 0.70, value that agrees well with the corresponding average experimental ratio 0.24/0.34 (see Fig. 6b). Moreover, as expected, the curve corresponding to the grinded case (i.e., texture density of 0%) is linear. The straight line added in Fig. 9 was also obtained under the condition to obtain the same normal pressure force as those of cases 11% and 50% of LST. The resulting film thickness of the grinded case was 8μm. Once again, the ratio between the friction coefficients of cases 11% of LST and grinded condition is 0.80, value that agrees well with the corresponding average experimental ratio 0.35/0.43 (see Fig. 6b).

Fig. 8.

(a) Relative pressure diagrams of LST with densities of 11% and 50% b) vortex formation in the center of dimples for the aforementioned densities.

(0.15MB).
Fig. 9.

Relative pressure distribution along the x-coordinate for the LST with densities of 11% and 50% for a tangential velocity of 0.2m/s.

(0.1MB).

The experiments showed that higher LST densities present lower friction coefficient, while the numerical analysis has brought out that the decrease of the friction coefficient can be associated to a higher hydrodynamic pressure and the formation of vortex of lower magnitude in the dimples. The reason of the magnitude attenuation in higher textured surface density is because the dimples are close between each other, which favor a lower distortion of the streamlines and, ultimately, reduces the friction coefficient. The results found in the present work present some differences with the friction results reported in Refs. [23] and [25]. Here, higher densities of textured surfaces (50%) with deeper dimples (40μm) combined with a graphite-based lubricant have shown better friction capabilities, whereas the aforementioned works stated that this desirable condition is achieved with low densities of textured surfaces (10–12%) with shallow dimples (2–8μm) combined with a different type of lubricant. Then, four major differences can be identified as responsible for these differences: type of lubricant, depth of dimples, contact pressure (although the initial value is only considered here, the wear of the pin will modify that value) and the temperature of the process. In the present study, our aim was to analyze deeper dimples and graphite-based lubricants, because it is expected to use this LST technology in hot-forging dies and components to enhance their lifespan. In short, as a smaller friction coefficient was found for LSTs of high density with respect to a grinded surface, this can be attributed to several aspects: firstly, a larger number of dimples induce a larger film thickness, as reported by Tala-Ighil et al. [6] and Cong and Konshari [7], but also it could also be related to a lower distortion of the streamline due to the proximity of the dimples leading, subsequently, to a less intense vortex formation.

4Conclusions

The present work successfully evaluates the friction characterization of three different graphite-based lubricants diluted in water up to 5% concentration at room temperature on various types of textured surfaces. Therefore, the following aspects can be summarized from this research work:

  • The laser texturing was performed in a material surface with a maximum height of the roughness profile of 5.98±1.76μm. A decrease of the friction coefficient up to 0.24 (a decrease of 41.6% with respect to the grinded surface) was found when higher density of textured surface is combined with lubricant B (graphite size of 1.93±0.99μm and an effective viscosity of 25mPa.s for the tested conditions).

  • The low viscosity, the size of the graphite embedded in the lubricant and the density of the LST have been crucial parameters to affect the friction coefficient. Smaller size of the particles of graphite facilitates the filling of the dimples of the textured surfaces, helping to ensure continuity in the lubricant layer between surfaces in starved conditions. Besides, the higher filled dimples with graphite particles seems to affect the cavitation effect increasing the pressure build-up and, consequently, decrease the friction coefficient.

  • Thanks to the experiments we have identified the lubrication regime for our operating conditions that was found to behave in the hydrodynamic lubrication regime for the textured surfaces. The numerical simulation exhibits that a higher LST density has validated the decrease of the friction coefficient found in the experimental trials. This is attributed to the formation of vortex in the dimples, where lower magnitudes of vortexes are found when the dimples are close between each other (higher textured surface density scenario) and, consequently, a lower distortion of the streamlines that reduces the friction coefficient.

In future work, this kind of textured surfaces will be implemented in a forging matrix to study the wear evolution compared with a non-treated surface lubricated at warm and hot forging processes. The combination of graphite-based lubricants and textured surfaces with deep dimples have showed a significant decrease of the friction coefficients as the textured surface density increases. This application presents a huge potential in forging matrices and components, since deep dimples are required to avoid that the textured surface disappear in the first forging blow. In this sense, lifespan and friction coefficient can be analyzed in a real industry scenario with complex geometries.

Conflict of interest

I would like to mention that there are no other author’s professional and/or financial affiliations that may have biased this research work.

Acknowledgments

This work was funded by the Serra Húnter program (Generalitat de Catalunya) reference number UPC-LE-304 and the National Council for Scientific and Technological Research of Chile (Fondecyt projects 3180006 and 1180591). We are also grateful to Soledad Pereda from INTI-Mecánica, Ing. César Guereta from Sierra Technology Group, Alejandro Bacigalupe from INTI-Caucho and Dr. José Di Paolo of Universidad Nacional de Entre Ríos for all their valuable help and support to achieve the present research work.

References
[1]
W. Steen, J. Mazumder.
Láser material processing.
4th edition, Springer Verlag, (2010), http://dx.doi.org/10.1007/978-1-84996-062-5
[2]
G. Campana, D. Martinez Krahmer.
Aplicaciones industriales de la tecnología láser, Cuadernillo Tecnológico, INTI – unión Europea.
[3]
A.J. Sánchez Egea, N. Deferrari, G. Abate, D. Martínez Krahmer, L.N. López de Lacalle.
Short-cut method to assess a gross available energy in a medium-load screw friction.
Press Metals, 8 (2018), pp. 1-10
[4]
A. Shihomatsu, S. Tonini Button, I. Bento da Silva.
Tribological behavior of laser textured hot stamping dies.
Adv Tribol, 8106410 (2016), pp. 1-16
[5]
M. Sulaiman, P. Christiansen, N. Bay.
The influence of tool texture on friction and lubrication in strip reduction testing.
Lubricants, 5 (2017), pp. 1-11
[6]
N. Tala-Ighil, M. Fillon, P. Maspeyrot.
Effect of textured area on the performances of a hydrodynamic journal bearing.
Tribol Int, 44 (2011), pp. 211-219
[7]
S. Cong, M. Konshari.
Effect of dimple’s internal structure on hydrodynamic lubrication.
Tribol Lett, 52 (2013), pp. 415-430
[8]
Y. Henry, J. Bouyer, M. Fillon.
An experimental analysis of the hydrodynamic contribution of textured thrust bearings during steady state operation - Comparison with the untextured parallel surface configuration.
Arch Proc Inst Mech Eng Part J J Eng Tribol 1994-1996, 208-210 (2015), pp. 362-375
[9]
H. Zhang, M. Hafezi, G. Dong, Y. Liu.
A design of coverage area for textured surface of sliding journal bearing based on genetic algorithm.
[10]
H.A. González Rojas, A.J. Sánchez Egea, J.A. Travieso-Rodríguez, J. Llumà i Fuentes, J. Jorba Peiró.
Estimation of the polishing time for different metallic alloys in surface texture removal.
Mach Sci Technol, 22 (2018), pp. 729-741
[11]
Y. Wu.
Study of interface friction reduction using laser micro-textured die surfaces in metal forming.
[12]
P. Šugár, J. Šugárová, M. Frnčík.
Laser surface texturing of tool steel: textured surfaces quality evaluation.
Open Eng, 6 (2016), pp. 90-97
[13]
A.J. Sánchez Egea, A. Rodríguez, D. Celentano, A. Calleja, L.N. López de Lacalle.
Joining metrics enhancement when combining FSW and ball-burnishing in a 2050 aluminium alloy.
Surf Coat Technol, (2019), pp. 327-335
[14]
S. Dzionk, B. Scibiorski, W. Przybylski.
Surface texture analysis of hardened shafts after ceramic ball burnishing.
[15]
I. Etsion.
State of the art in laser surface texturing.
[16]
P. Lu, R. Wood, M. Gee, L. Wang, W. Pfleging.
The friction reducing effect of square-shaped surface textures under lubricated line-contacts—an experimental study.
Lubricants, 4 (2016), pp. 1-13
[17]
Y. Xing, J. Deng, Z. Wu, F. Wu.
High friction and low wear properties of laser-textured ceramic surface under dry friction.
Opt Laser Technol, 93 (2017), pp. 24-32
[18]
S.C. Vlădescu, A.V. Olver, I.G. Pegg, T. Reddyhoff.
Combined friction and wear reduction in a reciprocating contact through laser surface texturing.
Wear, 358-359 (2016), pp. 51-61
[19]
A. Dunn, K.L. Wlodarczyk, J.V. Carstensen, E.B. Hansen, J. Gabzdyl, P.M. Harrison, et al.
Laser surface texturing for high friction contacts.
Appl Surf Sci, 357 (2015), pp. 2313-2319
[20]
L. Yang, Y. Ding, B. Cheng, J. He, G. Wang, Y. Wang.
Investigations on femtosecond laser modified micro-textured surface with anti-friction property on bearing steel GCr15.
Appl Surf Sci, 434 (2018), pp. 831-842
[21]
Y. Wan, D. Xiong, J. Li.
Cooperative effect of surface alloying and laser texturing on tribological performance of lubricated surfaces.
J Cent South Univ Technol, 17 (2010), pp. 906-910
[22]
M. Geiger, U. Popp, U. Engel.
Excimer laser micro texturing of cold forging tool surfaces -Influence on tool life.
CIRP Ann Manuf Technol, 51 (2002), pp. 231-234
[23]
J. Schneider, D. Braun, C. Greiner.
Laser textured surfaces for mixed lubrication: influence of aspect ratio, textured area and dimple arrangement.
Lubricants, 5 (2017), pp. 1-12
[24]
M. Scaraggi, F. Mezzapesa, G. Carbone, A. Ancona, D. Sorgente, P. Lugara.
Minimize friction of lubricated laser-microtextured-surfaces by tuning microholes depth.
Tribol Int, 75 (2014), pp. 123-127
[25]
D. Bijani, E. Deladi, M. de Rooij, D. Schipper.
The influence of surface texturing on the film thickness in starved lubricated parallel sliding contacts.
Lubricants, 6 (2018), pp. 1-19
[26]
D. Gropper, W. Ling, T. Harvey.
Hydrodynamic lubrication of textured surfaces: a review of modeling techniques and key findings.
Tribol Int, 94 (2016), pp. 509-529
[27]
A.J. Sánchez Egea, V. Martynenko, G. Abate, N. Deferrari, D. Martinez Krahmer, L.N. López de Lacalle.
Friction capabilities of graphite-based lubricants at room and over 1400 K temperatures.
Int J Adv Manuf Technol, 102 (2019), pp. 1623-1633
[28]
R. Long, P. Kelly, S. Sun, J. Feng, X. Wang, W. Li.
The influence of pits on the tribological behavior of grey cast iron under dry sliding.
Math Probl Eng, 8767895 (2018), pp. 1-9
[29]
S. Abachi.
Wear analysis of hot forging dies.
Middle East Technical University, (2004),
[30]
M. Cruchaga, E. Oñate.
A finite element formulation for incompressible flow problems using a generalized streamline operator.
Comput Methods Appl Mech Eng, 143 (1997), pp. 49-67
[31]
W.W.F. Chong, M. De la Cruz.
Elastoplastic contact of rough surfaces: a line contact model for boundary regime of lubrication.
Meccanica, 49 (2014), pp. 1177-1191
[32]
R.K. Gunda, S.K.R. Narala.
Tribological studies to analyze the effect of solid lubricant particle size on friction and wear behaviour of Ti-6Al-4Valloy.
Surf Coat Technol, 308 (2016), pp. 203-212
[33]
A.M. Kovalchenko, A. Erdemir, O.O. Ajayi, I. Etsion.
Tribological behavior of oil-lubricated laser textured steel surfaces in conformal flat and non-conformal contacts.
Mater Perform Charact, 6 (2017), pp. 1-23
[34]
L. Rapoport, A. Moshkovich, V. Perfilyev, I. Lapsker, G. Halperin, Y. Itovich, et al.
Friction and wear of MoS2 films on laser textured steel surfaces.
Surf Coat Technol, 202 (2008), pp. 3332-3340
Copyright © 2019. The Authors
Journal of Materials Research and Technology

Subscribe to our newsletter

Article options
Tools
Cookies policy
To improve our services and products, we use cookies (own or third parties authorized) to show advertising related to client preferences through the analyses of navigation customer behavior. Continuing navigation will be considered as acceptance of this use. You can change the settings or obtain more information by clicking here.