Effects of surface texturing on the frictional behaviorof cast iron surfaces

Beomkeun Kim a,n, Young Hun Chae b, Heung Soap Choi c

a High Safety Vehicle Core Technology Research Center, Inje University, 607 Obang-Dong, Gimhae, Gyeongnam 621-749, Republic of Koreab Department of Mechanical Engineering, Kyungpook National University, 1370 Sankyuk-Dong, Pook-Gu, Daegu 702-701, Republic of Koreac Department of Mechanical and Design Engineering, Hongik University, 2639 Sejong-Ro, Jochiwon-Eup, Sejong 339-701, Republic of Korea

a r t i c l e i n f o

Article history:Received 19 June 2013Received in revised form1 October 2013Accepted 8 October 2013Available online 15 October 2013

Keywords:Surface textureLaser machiningCoefficient of frictionDepth to diameter ratio

a b s t r a c t

The purpose of this study is to investigate the effects of the geometry and distribution of microdimpleson the frictional behavior of surfaces for applications in automotive engines. A square array of microscalecircular dimples was selected as the texture pattern. A laser beam was used to create microdimples withvarious dimensions on cast iron surfaces. Frictional tests were performed with selected loads and speedsto simulate the operation conditions of automotive engine parts. The effects of dimple distribution werealso investigated. The aspect ratio of the dimples was found to be the most significant factor, while theeffect of the surface density of the dimples on the coefficient of friction was found to be only marginal.

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1. Introduction

The increasing demand for environmentally friendly automo-biles has led to much research interest in improving the fuelefficiency of automotive engines. Because a significant proportionof the energy in an automotive engine is consumed by frictionallosses, the tribology of the mechanical parts is an important factorin determining the engine efficiency. Automotive engine partsexperience more than one regime of lubrication during theiroperation. For example, the lubrication regimes associated with acam and follower are boundary, mixed and elastohydrodynamic [1].The lubrication regimes for typical automotive engine parts areshown in Fig. 1 [1]. Modifying the lubrication conditions for a givenautomotive engine part may potentially improve the efficiency ofthe system. Vehicle performance could also be improved by utiliz-ing reduced-friction engines.

The effects of dimples on a surface were first reported byEtsion et al. [2–4], who investigated the effect of surface texturingand the optimal geometric arrangement of the surface features,both theoretically and experimentally, for water-lubricated sealingring applications. They found that surface texturing substantiallyincreased the load- carrying capacity of bearing surfaces. It is alsowell known that surface texturing of solid surfaces modifies thefrictional and wear properties. Dumitru et al. [5] investigated the

effect of surface textures using tribological tests on laser-structured substrates. They reported that the lifetimes of laser-processed samples increased significantly in comparison withunstructured samples. Menezes et al. [6] studied the effects ofsurface roughness and textures on the coefficient of friction;however, they only examined the effect of the existence ofdimples, and did not investigate their geometry. Wang et al.[7,8] investigated the effects of microdimples on the load-carrying capacity of SiC thrust bearings. The contact surface wastextured by reactive ion etching, and water lubrication was used inthe tests. They showed that the textured surface was able tomaintain hydrodynamic lubrication for a longer time than thenon-textured surface. Andersson et al. [9] demonstrated thebenefits of laser-textured tool surfaces for friction reduction. Theyfound that laser-textured patterns significantly reduced frictionand wear under lubricated sliding conditions. They performedexperiments using three different types of oil, but did not includesufficient variation in the dimensions of the dimples to investigatethe effect of their geometry. Wakuda et al. [10] studied the frictionalproperties of dimpled silicon nitride ceramic surfaces against steel.They evaluated samples with a variety of microdimple dimensions,under boundary or mixed lubrication conditions, and observed thatthere was a critical dimple size, below which the texturing wasineffective. Petterson and Jacobson [11] performed friction tests onsteel surfaces textured with a diamond tool. They reported that thecoefficients of friction of the textured surfaces indicated improvedlubrication at high pressure and low sliding speed. Nakano et al.[12] investigated the relationship between texture geometry and

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n Corresponding author. Tel.: þ82 11 296 3816; fax: þ82 55 320 3439.E-mail address: mechkbk@inje.ac.kr (B. Kim).

Tribology International 70 (2014) 128–135

coefficients of friction by testing microtextured surfaces preparedby shot blasting. They found that a dimpled pattern reduced thecoefficients of friction, whereas a grooved pattern increased them.Kovalchenko et al. [13] studied the impact of laser surface texturingon lubricating regime transitions. They observed that laser surfacetexturing could reduce the friction on components operating in aboundary-lubricated regime. This study included different sizeddimples, but focused on the tribological behavior rather than theeffects of the dimple dimensions. Voevodin [14] explored theapplications of laser-texturing the surfaces of hard TiCN coatingswith adaptive solid lubrication. Tests revealed increased wear lifefor specimens employing the dimple reservoir concept. Borghi et al.[15] investigated the effects of surface texturing on nitride steel.They showed that texturing the surface reduced the coefficient offriction, and avoided the transition from the hydrodynamic regimeto the mixed or boundary lubrication regime, resulting in anincrease in the wear lifetime. That study was limited to specimenswhere the dimple dimensions were not varied. Etsion et al. [16–19]conducted experimental and theoretical studies to investigate thefriction-reducing effects of surface texturing on automotive compo-nents. They suggested using textured surfaces for piston rings toachieve a reduction in the coefficient of friction, and they conductedexperimental investigations to support their theoretical estimates ofthe effect of surface texturing using a novel test rig for thereciprocating automotive components. Ren et al. [20] conductednumerical analyses to determine the effect of the distribution ofshallow dimples on the tribological properties of a surface. Gollochet al. [21] investigated the benefits of laser-structured cylinderliners by carrying out a series of tests on a single-cylinder dieselengine. They found that a laser-structured liner not only reducedfrictional losses and oil consumption, but also decreased cylinderwear. Park et al. performed computational fluid dynamics (CFD)analyses to investigate the lubrication characteristics of an infinitelylong slider bearing with dimples, and found that the pressuredistribution was strongly related to the dimple dimensions [22].

All of these studies indicate that textured surfaces (whether laser,chemically or mechanically structured) offer the benefit of reducedcoefficients of friction, not only in the hydrodynamic regime, butalso in the mixed or boundary lubrication regime. This leads todecreased wear on solid surfaces. However, to date there has beeninsufficient investigation of the effect of the dimple geometry onthe tribological behavior for applications in automobile engines.

The purpose of this study was to investigate the effects of thegeometry and distribution of microdimples on the tribologicalbehavior of surfaces for applications in automobile engines. Sur-face texturing has proved to be an effective way of improving thetribological behavior of contact surfaces. As found in previousstudies, surface texturing increased load-carrying capacity [2–4].While this aspect of surface texturing is relevant to automotiveengine parts, the scope of this study was limited to frictionreduction. In this study, the friction-modifying effects of texturingwere examined, and relationships between the geometry and thedistribution of microdimples and the coefficients of friction wereinvestigated for the different sliding velocity, viscosity of lubricantand contact pressure, with a focus on piston rings, cam followers,and engine bearings. Microtextured cast iron surfaces were pre-pared by laser processing, and experiments with various loads andspeeds were conducted under a thin layer of oil (by removingexcess oil from the surface) to simulate the operating conditions ofautomotive engine parts.

2. Experiments

2.1. Test equipment

Friction tests were carried out using a pin-on-disk tribometer[23]. The upper pin was loaded against the surface of a flat diskspecimen. The loading direction was parallel to the axis of rotation,and the magnitude of the normal force was controlled by addingdead weights on the upper pin. The frictional force was recordedusing strain gauges attached to the holder. The coefficient offriction was determined using these two force values. A schematicdiagram of the tribometer and the test setup is shown in Fig. 2. Thespeed of the test was controlled by changing the rotational speedof the disk or adjusting the length of the arm holding the pin.

2.2. Test specimens

The pin and disks were prepared from cast iron, which is suitablematerial for automotive engine parts such as liners, piston rings, orbearings. Table 1 shows an elemental analysis of the cast iron materialused in this study. One end of the pinwasmachined as a sphere with adiameter of 8 mm and a flat area (Fig. 3). The other end was machinedso that it could be attached to the arm of the tribometer. The final flatcontact area created on the pin was 3.3 mm in diameter. The surfaceroughness of the contact area of the pin was 0.8 μm Rz. The diskspecimens were also made from cast iron, each with a diameter of60 mm and a thickness of 5 mm. Surface textures, consisting ofmicrodimples of various sizes and depths, were fabricated on thedisks by laser-beam machining. Table 2 lists the surface texturingspecifications of the various specimens used in this study. The surfacearea to density ratio (total dimple area/total surface area) ranged from10% to 30%. The diameters and depths of the microdimples werecontrolled by adjusting the pulse energy of the laser. AYAG laser (AHT-SE010T model, λ¼1064 nm, tpulseE15 ns) was used to create themicrodimples on the disks. By trial and error under various laser-processing conditions, appropriate laser parameters were establishedto generate the desired pattern sizes. Table 3 lists the laser-processingparameters and the corresponding dimple sizes. For the cast iron

Fig. 1. A modified Stribeck curve associated with automotive engine parts [1].

B. Kim et al. / Tribology International 70 (2014) 128–135 129

material, a pulse energy of 24.4W was used to create dimples with adiameter of 106 μm and a depth of 14.84 μm.

Each disk specimen was moved laterally via a high-precisionXY-translation stage. A diagram of the laser-beam machining setupis shown in Fig. 4. After laser machining, the craters that formedaround the microdimples were removed by manual grinding withabrasive emery paper. Polishing with alpha alumina powderfollowed the grinding process, resulting in a surface roughnessof 0.8 μm Rz. The roughness of the textured surfaces was measuredon the upper area between the dimples. Fig. 5 shows three-dimensional (3D) scanning laser microscopy images of the micro-dimples created on the cast iron surfaces. Table 4 lists measure-ment results for five randomly selected laser-machined dimplesafter polishing. The diameters of the dimples were close to thetarget dimensions, but the deviations from the target dimensionswere greater for the depths of the dimples than for the diameters.Fig. 6 shows scanning electron microscopy (SEM) images of thetextured surfaces.

2.3. Experimental procedures

Tribological tests of 145 specimens were conducted using thepin-on-disk tribometer. Prior to each test, the pins and disks weresonicated in alcohol to remove metal fragments and oil from thesurface. Oil was applied to the top surface of each disk, and excessoil was removed using a rubber blade under constant pressure.The properties of the oil used in this study, which did not containany extreme pressure additives, are listed in Table 5.

The measurements were started immediately after the oil wasapplied, and continued until the coefficient of friction converged.Non-textured specimens were used, as well as specimens withcircular dimples. The duration of the measurements were deter-mined by considering the type of specimen and the lubricationparameters (i.e., sliding velocity� viscosity/contact pressure).Here, the contact pressure was the total normal force betweenthe mating surfaces and can be considered as the load-carryingcapacity. The coefficients of friction converged over a relatively

Fig. 2. Equipment setup for the tribology test.

Table 1Elemental analysis of the FC 25 cast iron used in this study.

Elemental composition (wt%) C Si Mn P S Cr Cu B Fe3.16 2.35 0.66 0.21 0.083 0.19 0.25 0.065 Bal.

Fig. 3. Pin and disk specimens. (a) Pin, (b) Disk.

B. Kim et al. / Tribology International 70 (2014) 128–135130

short distance (from 130 to 250 m) for the textured specimens. Forthe non-textured specimens, however, the coefficients of frictiononly converged over a short distance at the high and mid-range ofthe lubrication parameters (0.462 to 2.310); at the low range of thelubrication parameters (0.0369 to 0.0972), they converged over alonger distance (from 300 to 700 m). Tests were carried out withthe aim of determining the coefficient of friction of the variouslaser-textured surfaces. Table 6 lists the conditions for each test.

3. Results and discussion

The frictional behavior of textured and non-textured plates wascompared. There were significant differences in the frictionalbehavior of the test samples at low values of the lubricationparameter. At a lubrication parameter of 0.0369, the lubricationregime changed, and the coefficient of friction increased as the pinbegan to slide on the non-textured plate. The coefficient of frictionconverged to a value of 0.343 after sliding a distance of 650 m.A similar trend was observed at a lubrication parameter of 0.0972.The post-test oil residue on the non-textured plates revealed thatthe oil film became mixed with wear particles during the test, andno longer lubricated the sliding movement of the pin against theplate. This shows that the system was in the boundary lubricationregime.

The pin slid smoothly on the surface of textured plates for alubrication parameter of 0.0369, and the coefficient of frictionremained at a relatively low value of 0.171. The coefficient offriction converged relatively quickly compared with the case of a

non-textured plate. The oil films on the textured plates alsoremained relatively clean, since the dimples were able to retainnot only the lubricants, but also any wear particles that wereformed during the tests [12,15]. Textured plates with differentdimple dimensions followed similar trends for low lubricationparameters. Fig. 7 compares the coefficients of friction betweenthe textured and non-textured plates measured for a lubricationparameter of 0.0369 over a long sliding distance. The texturedplates had regular arrays of circular dimples with diameters of106 μm, depths of 14.84 μm, and surface density ratios of 10%.

Tribological measurements of the textured and non-texturedplates with different normal loads (from 1.47 to 14.70 N) anddifferent speeds (from 0.063 to 0.340 m/s) were performed toinvestigate the various ranges of the lubrication parameter. Eachtest continued until the coefficients of friction converged; theconverged coefficient of friction was measured at the end of eachtest. The results showed that the coefficients of friction convergedbetween 130 m and 250 m for most samples. Fig. 8 shows thedifferences in frictional behavior between the textured and non-textured plates with respect to the lubrication parameter. Theseresults indicate that all samples followed the trends of previousstudies [13,15]. Typical Stribeck curves with a transition from theboundary to mixed lubrication regime were obtained for the non-textured plates as the lubrication parameter decreased, whereasno transition was detected for the textured plates. At low valuesof the lubrication parameter (0.037 and 0.097), the coefficientsof friction of the non-textured plates were high, while thecoefficients of friction of the textured plates remained low.As the lubrication parameter increased, the coefficients of frictionof the non-textured plates dropped to the level of the texturedplates. When the lubrication parameter increased above 1.5, thecoefficients of friction of both plates tended to increase slightly.All textured plates followed the same trends. Fig. 9 shows thefrictional behavior of the textured plates with different dimplediameters in terms of the lubrication parameter.

The tests were carried out with respect to two different para-meters: surface area density ratio and depth to diameter ratio.Samples with three different surface area density ratios (10%, 20%,and 30%) and two different depth to diameter ratios (0.14 and 0.30)were investigated. Three different test samples were machined foreach combination of surface area density ratio and depth todiameter ratio. The friction tests were repeated with three differentsamples for each test condition, and the measured coefficients offriction were averaged. Fig. 10 shows the coefficients of friction asfunctions of the surface area density ratio, summarized from theresults of the basic friction tests. At low values of the lubricationparameter (0.037 and 0.097), the difference between the texturedand non-textured plates was significant. Similar trends were foundfor the textured plates with dimple diameters of 106 μm and130 μm, as shown in Figs. 11 and 12. For moderate values of thelubrication parameter (0.462, 0.924, and 1.382), no significant differ-ences between the non-textured and textured plates were observed.At high values of the lubrication parameter (1.848 and 2.310), no

Table 2Specimen specifications.

Specimenno.

Properties of the dimples

Diameter(μm)

Depth(μm)

Depth todiameterratio

Distance betweenconsecutive dimples(μm)

Surface areadensityratio (%)

1 80 11.2 0.14 225 102 80 11.2 0.14 158 203 80 11.2 0.14 130 304 80 24 0.30 225 105 80 24 0.30 158 206 80 24 0.30 130 307 106 14.84 0.14 303 108 106 14.84 0.14 212 209 106 14.84 0.14 174 3010 106 31.8 0.30 303 1011 106 31.8 0.30 212 2012 106 31.8 0.30 174 3013 130 18.2 0.14 365 1014 130 18.2 0.14 256 2015 130 18.2 0.14 208 3016 130 39 0.30 365 1017 130 39 0.30 256 2018 130 39 0.30 208 30

Table 3Laser-processing parameters for each specimen.

Laser processing no. Properties of the dimples Processing properties

Diameter (μm) Depth (μm) Aperture (μm) Beam Expander Frequency (kHz) Current (A) Pulse per dot

1 80 11.2 2.0 4� 10 24.5 142 80 24 2.0 4� 10 24.5 263 106 14.84 2.3 4� 10 23.5 174 106 31.8 2.0 4� 10 28 265 130 18.2 2.6 3� 10 23 226 130 39 2.6 3� 10 23 42

B. Kim et al. / Tribology International 70 (2014) 128–135 131

differences between the test samples were identified. When thelubrication parameter was high and the depth to diameter ratio was0.3, the textured plates exhibited slightly higher coefficients offriction than the non-textured plates, whereas the textured plateswith a depth to diameter ratio of 0.14 maintained similar coefficientsof friction. This phenomenon may result from the fluid dynamics ofthe oil near the dimples [16,20,22]. The results for the textured plateswith dimple diameters of 106 μm and 130 μm followed trends similarto those observed for a dimple diameter of 80 μm at moderate andhigh lubrication parameter values. Samples with a surface areadensity ratio of 10% exhibited the lowest coefficients of friction

among the textured plates under many test conditions. However, thedifferences were insignificant.

The curves in each graph were obtained at seven differentlubrication parameters: 0.037, 0.097, 0.462, 0.924, 1.382, 1.848, and2.310. The test results at low values of the lubrication parameter(0.037 and 0.097) indicated little dependency on the depth todiameter ratio, unlike the test results at moderate and highlubrication parameter values (0.462–2.310). In this regime ofhydrodynamic lubrication parameters (where elastohydrodynamicor hydrodynamic lubrication applies), the textured plates with adepth to diameter ratio of 0.14 had lower coefficients of frictionthan those with a depth to diameter ratio of 0.30. Similar resultswere obtained for the textured plates with dimple diameters of106 μm and 130 μm. Fig. 13 compares the measured coefficients offriction at a high lubrication parameter value (2.310) sorted by thedepth to diameter ratio, while Fig. 14 compares those sorted by thesurface area density ratio. In the high lubrication parameterregime, the variation due to the depth-to-diameter ratio wasgreater than that due to the surface area density. This is consistentwith the results of Ronen et al. [16], where the simulated optimumdepth-to-diameter ratio of textured plates was found to be near0.14 in the high-lubrication parameter regime. The surface areadensity was also found to have little effect on the coefficient offriction, which is also consistent with the simulation analysisreported in Ref. [16]. The coefficient of friction of was morestrongly related to the dimensions of the dimples than to the

Fig. 4. Diagram of the laser-beam machining setup.

Fig. 5. Scanning laser microscopy 3D images of microdimples created on the disks. (a) Scanned image of a dimple and (b) contours of the scanned image.

Table 4Dimple dimensions.

Dimple type Target dimension (μm) Random measurements results (μm)

Average Std. deviation

Type #1 Diameter 80 81.25 2.20Depth 11.2 10.64 1.63Depth 24 24.08 2.15

Type #2 Diameter 106 105.6 2.35Depth 14.84 15.43 1.93Depth 31.8 31.67 2.76

Type #3 Diameter 130 132.8 2.77Depth 18.2 19.34 3.29Depth 39 38.58 1.63

B. Kim et al. / Tribology International 70 (2014) 128–135132

surface area density of the dimples. This may result from the fluiddynamics of the oil near the dimples [16,20,22].

4. Conclusion

Tribological measurements with various geometric parameterswere performed on textured plates to investigate the effect of

texturing on friction reduction. A comparison between texturedand non-textured plates showed that textured plates maintainedelastohydrodynamic or mixed lubrication regimes longer thannon-textured plates under a given lubrication condition.

Friction test revealed that the measured coefficients of frictionfor the non-textured plates, plotted as functions of the lubricationparameter, took the form of typical Stribeck curves with a transitionfrom the boundary to mixed lubrication regime, whereas for thetextured plates, low coefficients of friction were maintainedthroughout the entire range of lubrication parameter values. Thefriction tests showed that the textured plates had markedly reducedcoefficients of friction at low values of the lubrication parameter,regardless of dimple diameter. However, texturing had little effecton the coefficients of friction at moderate and high values of thelubrication parameter.

Fig. 6. SEM images of the textured surfaces. (a) 1�magnification and (b) 100�magnification.

Table 5Oil properties.

Property Mineral oil (CAS 8042-47-5)

Density at 15 1C (kg/m3) 877Viscosity at 40 1C (mm2/s) 65–75Vapor pressure at 20 1C (mmHg) 0.001

Table 6Measurement conditions.

Test no. Parameters

Speed (m/s) Load (N) Lubrication parameter

1 0.0628 14.710 0.03692 0.0628 5.590 0.09723 0.262 4.903 0.4624 0.262 2.452 0.9245 0.392 2.452 1.3826 0.272 1.275 1.8487 0.340 1.275 2.310

Fig. 7. Coefficients of friction of the textured and non-textured plates during thelong range sliding.

Fig. 8. Coefficients of friction of the textured and non-textured plates vs. thelubrication parameter.

Fig. 9. Coefficients of friction of the textured plates with various texturingconditions vs. the lubrication parameter.

B. Kim et al. / Tribology International 70 (2014) 128–135 133

Friction tests were performed to investigate the effect of thedepth to diameter ratio, based on two different values of the ratio.At a high lubrication parameter value, the textured plates with adepth to diameter ratio of 0.14 had lower coefficients of frictionthan those with a depth to diameter ratio of 0.30, which waspredicted in the previous study of Ronen et al. [16]. At low valuesof the lubrication parameter, the depth to diameter ratio did notsignificantly affect the frictional behavior.

For surface area density ratio, only a marginal effect on frictionalbehavior was observed. Under some lubrication parameter conditions,the surface area density ratio had no apparent effect on the coefficientsof friction. Under these conditions, the effect of the depth to diameterratio was greater than that of the surface area density ratio. This alsowas in agreement with the numerical predictions of Ronen et al. [16].

Fig. 10. Coefficients of friction of the textured plates (dimple diameter¼80 μm) vs.surface area density for various lubrication parameters at depth to diameter ratio of(a) 0.14, (b) 0.30.

Fig. 11. Coefficients of friction of the textured plates (dimple diameter¼106 μm) vs.surface area density for various lubrication parameters at depth to diameter ratio of(a) 0.14, (b) 0.30.

Fig. 12. Coefficients of friction of the textured plates (dimple diameter¼130 μm)vs. surface area density for various lubrication parameters at depth to diameterratio of (a) 0.14, (b) 0.30.

Fig. 13. Comparison of coefficients of friction from two different depth to diameterratios at a high lubrication parameter value for various surface area densities.

B. Kim et al. / Tribology International 70 (2014) 128–135134

In this study, a basic tribological study of the effect of surfacetexturing was provided for applications in automobile engines.Advanced experiments considering operating conditions, asdescribed in Refs. [17–19,21], may provide more detailed data forapplication purposes in automobile engines.

Acknowledgement

This work was supported by the 2011 Inje University re-search grant.

References

[1] Priest M, Taylor CM. Automobile engine tribology-approaching the surface.Wear 2000;241:193–203.

[2] Etsion I, Kligerman Y, Halperin G. Analytical and experimental investigation oflase-textured mechanical seal faces. Tribol Trans 1999;42:511–6.

[3] Etsion I, Halperin G. A laser surface textured hydrostatic mechanical seal.Tribol Trans 2002;45:430–4.

[4] Etsion I, Halperin G, Brizmer V, Kligerman Y. Experimental investigation oflaser surface textured parallel thrust bearings. Tribol Lett 2004;17:295–300.

[5] Dumitru G, Romano V, Weber HP, Haefke H, Gerbig Y, Pflueger E. Lasermicrostructuring of steel surfaces for tribological applications. Appl Phys A2000;70:485–7.

[6] Menezes PL, Kishore SV, Kailas. Influence of surface texture on coefficient offriction and transfer layer formation during sliding of pure magnesium pin on080 M40 (EN8) steel plate. Wear 2006;261:578–91.

[7] Wang X, Kato K, Adachi K, Aizawa K. The effect of laser texturing of SiC surfaceon the critical load for the transition of water lubrication mode fromhydrodynamic to mixied. Tribol Int 2001;34:703–11.

[8] Wang X, Kato K, Adachi K, Aizawa K. Loads carrying capacity map for thesurface texture design of SiC thrust bearing sliding in water. Tribol Int2003;36:189–97.

[9] Andersson P, Koskinen J, Varjus S, Gerbig Y, Haefke H, Georgiou S, et al.Microlubrication effect by laser-textured steel surfaces. Wear 2007;262:369–79.

[10] Wakuda M, Yamauchi Y, Kanzaki S, Yasuda Y. Effect of surface texturing onfriction reduction between ceramic and steel materials under lubricatedsliding contact. Wear 2003;254 (369–363).

[11] Pettersson U, Jacobson S. Textured surfaces for improved lubrication at highpressure and low sliding speed of roller/piston in hydraulic motors. Tribol Int2007;40:355–9.

[12] Nakano M, Korenaga A, Korenaga A, Miyake K, Murakami T, Ando Y, et al.Applying micro-texture to cast iron surfaces to reduce the friction coefficientunder lubricated conditions. Tribol Lett 2007;28:131–7.

[13] Kovalchenko A, Ajayi O, Erdemir A, Fenske G, Etsion I. The effect of lasersurface texturing on transitions in lubrication regimes during unidirectionalsliding contact. Tribol Int 2005;38:219–25.

[14] Voevodin AA, Zabinski JS. Laser surface texturing for adaptive solid lubrication.Wear 2006;261:1285–92.

[15] Borghi A, Gualtieri E, Marchetto D, Moretti L, Valeri S. Tribological effects ofsurface texturing on nitriding steel for high-performance engine applications.Wear 2008;265:1046–51.

[16] Ronen A, Kligerman Y, Etsion I. Friction-reducing surface-texturing in reci-procating automotive components. Tribol Trans 2001;44:359–66.

[17] Ryk G, Etsion I. Testing piston rings with partial laser surface texturing forfriction reduction. Wear 2006;261:792–6.

[18] Ryk G, Kligerman Y, Etsion I. Experimental investigation of laser surfacetexturing for reciprocating automotive components. Tribol. Trans.2002;45:444–9.

[19] Ryk G, Kligerman Y, Etsion I, Shinkarenko A. Experimental investigation ofpartial laser surface texturing for piston-ring friction reduction. Tribol Trans2005;48:583–8.

[20] Ren N, Nanbu T, Yasuda Y, Zhu D, Wang Q. Micro textures in concentrated-conformal-contact lubrication: effect of distribution patterns. Tribol Lett2007;28:275–85.

[21] Golloch R, Merker GP, Kessen U, Brinkmann S. Functional properties ofmicrostructured cylinder liner surfaces for internal combustion engines.Tribotest 2005;11:295–388.

[22] Park TJ, Hwang YG, Sohn JD, Chung HG. CFD analysis of an infinitely long sliderbearing with two-dimensional micro-pockets. J KSTLE 2009;25:43–8.

[23] ASTM Ed., Standard test method for wear testing with a pin-on-diskapparatus, Annual Book of ASTM Standards G99 (2006).

Fig. 14. Comparison of coefficients of friction from three different surface areadensities at a high lubrication parameter value for two different depth to diameterratios.

B. Kim et al. / Tribology International 70 (2014) 128–135 135