Third body effects on friction and wear during fretting of steel contacts

Third body effects on friction and wear during fretting of steel contacts

Tribology International 44 (2011) 1452–1460 Contents lists available at ScienceDirect Tribology International journal homepage: www.elsevier.com/loc...

2MB Sizes 0 Downloads 42 Views

Tribology International 44 (2011) 1452–1460

Contents lists available at ScienceDirect

Tribology International journal homepage: www.elsevier.com/locate/triboint

Third body effects on friction and wear during fretting of steel contacts N. Diomidis n, S. Mischler Ecole Polytechnique Fe´de´rale de Lausanne (EPFL), Tribology and Interface Chemistry Group (SCI-STI-SM), CH-1015 Lausanne, Switzerland

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 May 2010 Received in revised form 20 January 2011 Accepted 28 February 2011 Available online 5 March 2011

Fretting wear proceeds through particle detachment from the contacting surfaces which, while trapped in the contact zone, can affect the frictional and wear response. Ball-on-flat fretting experiments were carried out between steel specimens under gross slip regime. A transition in the coefficient of friction was linked to a critical contact pressure. The microstructure and chemical composition of the third body evolve with the applied pressure. The evolution of the friction coefficient is strongly dependent on the third body properties. The wear is controlled by the applied load and thus the real contact area within the wear track. & 2011 Elsevier Ltd. All rights reserved.

Keywords: Fretting Debris Friction Wear

1. Introduction Mechanical vibrations can induce surface damage on contacting bodies due to relative oscillatory motion within the loaded contact zone. At displacement amplitudes, which are small compared to the contact size, this phenomenon is known as fretting. Fretting can occur in all quasi static loaded assemblies such as cables, electrical contacts, orthopedic implants, machine components, etc. It has been common lately to study fretting through the dissipated energy approach, which addresses the contact area as a whole [1–3]. Particularly, the fretting of steel contacts with regards to the fretting regime or the hardness of the contacting bodies has been previously reported [4–9]. A different approach to the study of fretting is to address the material fluxes within the contact zone by studying the behavior of the third body. The particularity of the mechanism of fretting is that, due to the small displacement, the central part of the contact zone is highly confined. Debris particles formed by plastic deformation (abrasion, adhesion, fatigue, etc.) of superficial layers of the first bodies, are momentarily trapped in the contact zone whose dimensions are orders of magnitude larger, and cannot easily escape [4]. Thus, after a few fretting cycles, the situation changes from a two to a three body contact consisting of the two rubbing specimens and the interface. This change needs to be taken into account for the interpretation of the experimental results. While a particle is part of the third body, it can change in chemical composition and morphology. The process of wear proceeds

n

Corresponding author. E-mail address: [email protected]fl.ch (N. Diomidis).

0301-679X/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.triboint.2011.02.013

through a series of steps, which occur continuously and concurrently. Finally, the third body particle is ejected from the contact zone and becomes a wear particle [10]. The role that the third body formed by the wear debris plays in fretting is an important one and can have different aspects [11]. It affects the displacement accommodation in the contact zone and thus affects the coefficient of friction [12,13], it can consist of hard abrading oxides and thus increase the wear, or it can separate the surfaces and have a protective role [9,14]. Different studies have been done lately on the effects of the amount of third body particles on the coefficient of friction [15] and the wear volume [16]. This work is aimed to investigate the third body effects in a steel-on-steel model contact. For this, a dedicated tribometer that allows to extract the third body thickness is used.

2. Experimental Fretting experiments were carried out using a ball-on-flat fretting tribometer made in-house. The tribometer consists of a stainless steel square frame with a stiffness in the horizontal direction of 109 N m  1. Motion of the lower sample is controlled by a piezo-actuator, through an elastic bearing. The actuator is equipped with a position sensor and a loop in its electronic controlling system permits to impose well-defined effective displacements. The difference between the command value of the piezo-actuator and the effective displacement of the elastic bearing center was found being o2% up to a slip amplitude of 180 mm. Further details on the tribometer are given in a previous publication [17]. 100Cr6 steel bearing balls with a diameter of 10 mm were cut and ground resulting in a circular flat area with a diameter of

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

8 mm. The resulting sections were polished with 3 mm diamond paste, ultrasonically cleaned in acetone, and used as the flat specimen. 100Cr6 steel bearing balls of different diameters were used as counterbodies. A fretting oscillation with a displacement of 110 mm at a frequency of 1 Hz was applied, while the applied load was varied between tests. All experiments were done in air at a temperature of 2471 1C and a relative humidity of 4777%. The experimental conditions tested are shown in Table 1. During the fretting experiments, the normal force and the tangential force were measured by a Kistler 9251A pre-loaded quartz force sensor. The vertical position of the counterbody was monitored by a Keyence LC2420 laser distance meter at a resolution of 0.01 mm. Each parameter was acquired at a sampling rate of 1000 points/s and, simultaneously, the mean value was calculated every second. Both mean and instantaneous values were stored at regular intervals of 1 and 60 s, respectively. The mean frictional coefficient was calculated by dividing the tangential force by the normal force when the ball was in the middle of the stroke. The worn surfaces were analyzed using optical microscopy, Scanning Electron Microscopy (Philips XL30 FEG) and Auger Electron Spectroscopy (PHI scanning Auger microscope using a 5 keV, 10 nA beam). AES FeMVV spectra were obtained after sputtering to an approximate depth of 8 nm. A 3D laser scanning profilometer (UBM Telefokus UBC14) was used to characterize the surface topography in and around the wear track of the flat specimen at a resolution of 500 points/mm. The volume of the wear track was determined by considering a semi-ellipsoidal shape with the axes corresponding to the length, width and

1453

depth of the track [19]. The wear volume of the ball counterbody was calculated by considering a spherical cap shape with the diameter measured by optical microscopy. Loose debris were removed from the wear tracks by gentle brushing, compressed air and ultrasonic cleaning in acetone prior of the measurement of the wear volumes.

3. Results 3.1. Friction Acquisition of transient values during fretting allows the plotting of fretting logs, i.e. three-dimensional graphical representations of the time evolution of the frictional force–displacement loops. Such diagrams are shown in Fig. 1 for tests carried out at a load of 5 and 20 N for 3600 s. In both cases a trapezoidal loop is formed, where both elastic deformation (the projection of the angled sides to the horizontal sides of the loop) and slip (the remaining length of the horizontal sides after subtraction of the projections) contribute to the displacement, indicative of a gross slip regime. The real displacement due to slip is smaller than the imposed displacement, and the elastic accommodation increases linearly with load. The slope of that straight line is 1.55  106 N/m and is indicative of the rigidity of the system consisting of the tribometer, the specimens and the fretting contact. Furthermore, the slip regime does not change during the course of an experiment, while the friction force reaches a maximum after a few tens of cycles, and then gradually decreases during the rest of the test.

Table 1 Experimental conditions of fretting experiments. The critical load at yield inception, Pc, as well as the ratio of the applied load to the critical load, P/Pc, are calculated according to [18]. For P/Pc o 1 the contact is elastic, while for P/Pc 4 1 the contact is elastic–plastic. In the case of elastic–plastic contact the Hertzian pressure and contact area are only given as approximations assuming a purely elastic contact. Counterbody diameter (mm)

Applied load (N)

Test duration (s)

Pc (N)

P/Pc

Max Hertzian contact pressure (GPa)

Hertzian contact area radius (mm)

20 10 10 6 6 4

5 10 20 7.16 20 20

3600 3600 3600 3600 3600 8, 110, 3600

341.29 85.32 85.32 30.72 30.72 13.65

0.01 0.12 0.23 0.23 0.65 1.47

0.51 1.01 1.27 1.27 1.79 2.34

0.07 0.07 0.09 0.05 0.07 0.06

Fig. 1. Fretting log diagrams from experiments carried out against (a) a counterbody with a diameter of 20 mm at a load of 5 N (P/Pc ¼0.01), and (b) a counterbody with a diameter of 10 mm at a load of 20 N (P/Pc ¼0.23).

1454

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

Fig. 2. Evolution of the coefficient of friction during fretting experiments at different loading conditions. The time at which the period of minimum coefficient of friction ends, t2, is indicated by arrows.

The evolution of the average coefficient of friction during fretting at different loading conditions is shown in Fig. 2. In all cases, the friction coefficient shows a peak around 0.8 during the first few seconds of the experiment (t1), and then goes through a period of minimum values between 0.6 and 0.75. At the end of the period that

the coefficient of friction is at a minimum (t2), which can last for up to a few hundred cycles, it increases again to reach a quasi steady state value around 0.8. For the rest of the experiment, the coefficient of friction shows a slow gradual decrease, in agreement with the fretting log diagrams (Fig. 1), and is characterized by local fluctuations.

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

The two time intervals, t1 and t2, exhibit a different relationship with the applied pressure: t1 is pressure independent at 1273 s for all tests, while t2 increases on increasing P/Pc. Additionally, the value of

1455

the coefficient of friction during the minimum period decreases on increasing pressure. 3.2. Vertical position of the counterbody

Fig. 3. Evolution of the vertical position of the counterbody during fretting experiments at different loading conditions.

The evolution of the vertical position of the counterbody during fretting experiments at different loading conditions is shown in Fig. 3. This parameter can be assumed to represent the difference between the wear depths of the flat specimen and counterbody, and the thickness of the third body in the contact. In most cases, the counterbody moves downwards during the experiment revealing the continuously increasing wear depths of the specimens. The final position of the counterbody at the end of the test decreases with the initial applied Hertzian contact pressure, except in the case of the test carried out at P/Pc ¼0.12. This indicates that in that specific case a larger amount of third body is trapped in the contact zone. The evolution of the coefficient of friction and the vertical position of the counterbody with a diameter of 20 mm during a fretting experiment at an applied load of 5 N (P/Pc ¼0.01) are shown in Fig. 4. After a few seconds of rubbing, the position of the counterbody slightly raises indicating material build-up in the contact. Afterwards, the descent of the counterbody indicates progressive material removal from the contact, i.e. wear. The data demonstrate a close correlation between the friction coefficient variations and the position of the counterbody. A large fluctuation in the friction coefficient corresponds to a rise and sudden fall in the position of the contact. These fluctuations are attributed to the formation of wear particles and to their ejection from the contact. Fig. 4 illustrates the important contribution of third body behavior to the coefficient of friction. 3.3. Microstructure and composition of the wear scars

Fig. 4. Evolution of the coefficient of friction and the vertical position of the counterbody during a fretting experiment against a counterbody with a diameter of 20 mm at a load of 5 N (P/Pc ¼ 0.01).

A representative optical micrograph of the wear scar and the surrounding area of the flat specimen after a fretting test against a counterbody with a diameter of 6 mm at a load of 20 N (P/Pc ¼ 0.65) for 3600 s is shown in Fig. 5. The wear scar has an elliptical shape and a large amount of wear particles, appearing red to the naked eye, is found at both ends of the wear scar, particularly in the fretting direction. The alignment of the wear debris with the fretting direction seems to suggest that the spread of the debris particles is caused by the kinetic energy transferred to them by the moving counterbody. Optical micrographs of the flat specimens and spherical counterbodies after fretting experiments against a counterbody with a diameter of 20 mm at a load of 5 N (P/Pc ¼0.01), and against a counterbody with a diameter of 4 mm at a load of 20 N (P/Pc ¼1.47)

Fig. 5. Optical micrograph of the wear scar of a flat specimen after a fretting experiment against a counterbody with a diameter of 6 mm, at a load of 20 N (P/Pc ¼ 0.65) for 3600 s. Fretting was done in the horizontal direction. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

1456

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

Fig. 6. Optical micrographs of wear scars on (a) the flat specimen and (b) the 20 mm counterbody after a fretting experiment at a load of 5 N (P/Pc ¼ 0.01) for 3600 s, and (c) the flat specimen and (d) the 4 mm counterbody after a fretting experiment at a load of 20 N (P/Pc ¼ 1.47) for 3600 s. Fretting was done in the horizontal direction. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Table 2 Chemical compositions based on AES of the different areas of a flat specimen after a fretting experiment against a counterbody with a diameter of 20 mm at a load of 5 N (P/Pc ¼ 0.01) for 3600 s. Peak energies and sensitivity factors are also indicated. Position

Gray area Red area Outside the wear track

Fig. 7. Auger electron spectra of the flat specimen after a fretting experiment against a counterbody with a diameter of 20 mm at a load of 5 N (P/Pc ¼0.01) for 3600 s at (A) the area outside the wear track, (B) the gray area inside the wear track, and (C) the red area inside the wear track. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

for 3600 s are shown in Fig. 6. There exist three microstructurally distinct areas within the wear tracks: a red colored area, a dark gray area, and a bright colored area with scratches belonging to the base metal. The chemical composition of the different areas within the wear track is revealed by AES (Fig. 7 and Table 2). The chemical composition indicates that the red areas consist exclusively of iron oxide, most probably Fe2O3, while no metallic iron is present as exhibited by the absence of the peak at 47 eV in Fig. 7C [20]. On the other hand, a metallic iron enriched oxide is present in the gray areas. This indicates that the gray areas most probably originate from compacted and surface oxidized metallic debris [21]. Outside the wear track, only metallic iron is found. Additionally, when comparing

Fe3, 706.5 eV, s ¼0.220 (at%)

O1, 516 eV, s ¼0.400 (at%)

62.94 43.14 39.36 38.29 90.79 91.47

37.06 56.86 60.64 61.71 9.21 8.53

the images of the flat specimens and the counterbodies from each experiment (Fig. 6) it is evident that the gray areas and the bright metallic areas are mirror images of each other. This indicates that after 3600 fretting cycles the base metal rubs only against compacted debris. The scratches present on the bare metallic areas indicate that the gray third body has abrasive properties, in agreement with [9]. Furthermore, the red area coverage decreases on increasing P/Pc, indicating that compaction and cohesion of third bodies is promoted at high pressures. Scanning electron micrographs of the wear track after a fretting test against a counterbody with a diameter of 4 mm at a load of 20 N (P/Pc ¼ 1.47)are shown in Fig. 8. The uncovered metal surface appears smooth indicative of mild oxidational type wear, while no cracks can be found. On the contrary, the gray oxide appears to be consisting of smaller compacted particles and cracks appear on its surface indicating its brittle nature. Optical micrographs of wear scars on the flat specimen and the 4 mm counterbody after a fretting experiment at a load of 20 N (P/Pc ¼ 1.47) after 8 and 110 cycles are shown in Fig. 9. After 8 s of rubbing, which is just before the initial peak in the friction coefficient (tot1), some slight discoloration has appeared on the surface of the samples, probably due to oxidation. Only a

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

1457

Fig. 8. Scanning electron micrographs of the wear track after fretting against a counterbody with a diameter of 4 mm at a load of 20 N (P/Pc ¼1.47), showing the smooth uncovered metal surface and the red area (a), and the black compacted surface oxidized debris (b). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 9. Optical micrographs of wear scars after a fretting experiment with a 4 mm counterbody at a load of 20 N (P/Pc ¼ 1.47) on (a) the flat specimen and (b) the counterbody after 8 s, and (c) the flat specimen and (d) the counterbody after 110 s. Fretting was done in the horizontal direction.

small amount of gray debris is noticed. After 110 s of rubbing, which is during the period that the friction coefficient goes through a minimum (t1 ot ot2), only the gray compacted oxidized metal debris and the bare metal surface are found.

measured after fretting. The accuracy of the measurements was 10 nm.

4. Discussion 3.4. Wear Cross sections of the wear scar of the flat specimen measured parallel and vertical to the fretting direction after a fretting experiment against a counterbody with a diameter of 10 mm a load of 10 N (P/Pc ¼0.12) for 3600 s are shown in Fig. 10. The wear volumes of the counterbody and the flat specimen, the total wear volume, the effective slip distance, the third body thickness in the contact, t2, and the coefficient of friction at t2 are shown in Table 3. In almost all cases the counterbody wears slightly more than the flat specimen. The third body thickness was calculated using the vertical position of the counterbody at the end of the fretting test (Fig. 3) and the wear depths of the specimens

The evolution of the wear volume of the counterbody with the product between the normal load and the total effective slip distance, which can be linked to the energy dissipated during fretting in the case where the friction coefficient in all tests can be assumed as equal [8,11,19] is shown in Fig. 11. The linear relationship found indicates that the Archard equation [22] describes adequately the wear measured during these fretting experiments. Thus, the wear coefficients have been calculated and are shown in Table 4. The wear coefficients are independent of third body thickness indicating that the wear of the specimens depends only on the applied load. The applied load is accommodated in the contact by deformation of asperities and is thus linked to the real contact area.

1458

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

Furthermore, the contact pressure at time t2, Pt2 , was calculated assuming a constant volumetric wear rate and neglecting elastic deformation. More specifically, the evolution of the radius a of the flat circular end formed on the spherical counterbody due to wear was calculated by assuming that the wear volume Vball is proportional to the fretting time tfretting according to Eq. (1). Vball ¼ Cw tfretting

ð1Þ

The proportionality constant Cw can be experimentally determined for each experiment by dividing the wear volume of the ball by the fretting duration (3600 s in all tests). The wear volume corresponds to the volume of a spherical cap of height h and radius a as described by Eqs. (2) and (3). Vball ¼ 1=3ph2 ð3rhÞ

ð2Þ

a2 ¼ h ð2rhÞ

ð3Þ

with r the radius of the ball. Since the wear depth on the present experiments is of the order of few micrometers Eqs. (2) and (3) can be simplified by assuming that (3r  h)ffi 3r and (2r h)ffi 2r. By combining Eqs. (1)–(3) one obtains: aðtÞ ¼ ð20:5 =p0:25 Þr 0:25 ðCw tfretting Þ0:25

ð4Þ

This method predicts quite well the wear after 110 cycles, giving a calculated contact radius of 92 mm, while 89 mm are measured from Fig. 9d. The evolution of the nominal contact pressure Pn (t) evolves thus during fretting due to the increase in the flat end area according to Eq. (5): Pn ðtÞ ¼ Fn=pa2 ðtÞ

ð5Þ

The obtained results are shown in Table 4. The transitions in the evolution of the coefficient of friction during a test show that both t2 and the coefficient of friction at t2 evolve with the initial loading conditions (P/Pc). On the other hand, the contact pressure at t2 is more or less constant for all

Fig. 10. Cross sections passing through the center of the wear scar on the flat specimen after a fretting experiment against a 10 mm counterbody at a load of 10 N (P/Pc ¼ 0.12) for 3600 s, parallel (top) and vertical (bottom) to the fretting direction.

Fig. 11. The evolution of the wear volume of the counterbody with the product of the normal load and the total effective slip distance.

Table 3 The wear volumes of the counterbody and the flat specimen, the total wear volume, the effective slip distance, the third body thickness, t2, and the coefficient of friction at t2 for all fretting experiments. Counterbody diameter (mm)

Applied load (N)

Test duration (s)

Vcounter (10  3 mm3)

Vflat (10  3 mm3)

Vtotal (10  3 mm3)

Effective slip distance (m)

3rd body thickness (mm)

t2 (s)

m at t2

20

5

3600

10

10

3600

10

20

3600

6

7.16

3600

6

20

3600

4

20

3600

0.348 0.352 0.729 0.722 0.756 0.706 0.314 0.431 0.647 1.34 1.04 0.856 3.79  10  2

0.317 0.241 0.563 0.385 0.651 0.680 0.468 0.410 0.756 0.700 0.581 0.576 –

0.664 0.592 1.292 1.107 1.407 1.386 0.781 0.841 1.404 2.040 1.622 1.432 –

0.7445 0.7329 0.6912 0.6789 0.5753 0.5789 0.7121 0.7078 0.5688 0.5868 0.5529 0.5796 0.01848

2.9 2.5 13.4 11.3 3.1 4.8 2.8 4.1 7.8 11.1 7.7 4.5 –

23 34 53 57 89 88 86 97 324 237 235 292 –

0.67 0.73 0.70 0.71 0.65 0.65 0.67 0.67 0.66 0.63 0.58 0.61 –

110

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

1459

Table 4 The wear coefficient of the counterbody and the flat specimen, the total wear coefficient, and the contact pressure at t2 for all fretting experiments carried out for 3600 s. Counterbody diameter (mm)

20 10 10 6 6 4

Applied load (N)

5 10 20 7.16 20 20

P/Pc

0.01 0.12 0.23 0.23 0.65 1.47

Kcounter (mm3/Nm)

Kflat (mm3/Nm)

Ktotal (mm3/Nm)

Pt2 (MPa)

9.34  10  5 9.59  10  5 1.06  10  4 1.06  10  4 6.57  10  5 6.10  10  5 6.15  10  5 8.51  10  5 5.69  10  5 1.14  10  4 9.41  10  5 7.39  10  5

8.51  10  5 6.57  10  5 8.14  10  5 5.68  10  5 5.66  10  5 5.87  10  5 9.17  10  5 8.08  10  5 6.65  10  5 5.97  10  5 5.26  10  5 4.97  10  5

1.78  10  4 1.62  10  4 1.87  10  4 1.63  10  4 1.22  10  4 1.20  10  4 1.53  10  4 1.66  10  4 1.23  10  4 1.74  10  4 1.47  10  4 1.24  10  4

300 245 389 377 593 613 437 351 438 356 512 507

tests at 426 7113 MPa. This indicates that it is a critical contact pressure, characteristic of a process that gives rise to the friction transition. The increase in t2 with the initial loading conditions can be ascribed to the larger number of cycles necessary to induce enough wear to decrease of the contact pressure to the critical value measured at t2 at larger initial pressures. During the first few cycles of the fretting experiments [23], the removal of surface contamination and native oxide film [13] leads to a mostly 2-body metal-to-metal contact giving rise to a peak in the coefficient of friction at time t1. Partial oxidation of the metal surfaces also occurs. Wear at this early period leads to the formation of partially oxidized metallic wear debris. Due to the high contact pressure, the debris particles are compacted into an abrasive gray third body layer, which is in contact with the bare metal surface. The presence of the compact gray layer increases the distance between the first bodies, avoiding metal-to-metal contact, and thus decreasing the coefficient of friction. The dependence of the friction coefficient during this minimum period on the initial contact pressure can be ascribed to the fact that the debris will be more compacted at high initial pressures. This can facilitate the displacement accommodation thus leading to a decrease in the friction coefficient. This phenomenon can also explain the larger amount of gray debris found at the end of fretting experiments carried out at high initial contact pressures. At time t2, when the critical contact pressure Pt2 has been reached due to wear, the pressure is not high enough to compact the debris into the gray third body. The debris particles are thus able to move more freely within the contact zone. Alternatively, the pressure is not high enough to further detach metal particles and wear proceeds by removal of the oxide film continuously created on exposed bare metal surfaces (oxidative wear). Both mechanisms lead to a complete oxidation of part of the third body, which is transformed into the red Fe2O3 oxide. At this pressure, a friction transition takes place, ending the period of minimum friction values and the coefficient of friction increases again. Beyond t2, a quasi steady state between the formation of debris, their oxidation, and their ejection from the contact is achieved and is characteristic of the remaining period of the fretting experiments. This dynamic state is reflected in the local fluctuations of the coefficient of friction.

5. Conclusions Steel on steel fretting experiments under gross slip regime at elastic and elastoplastic initial loading conditions were carried

out to investigate the effects of third body behavior on the wear and the coefficient of friction.

 The wear rate was found to be independent of the third body

 

behavior in the contact but depended on the applied load and the real contact area within the wear track in agreement with the Archard theory. The coefficient of friction evolves with time, particularly in the first few hundred cycles, depending on the evolution of the contact zone with time and the initial applied pressure. A critical pressure exists at which a transition to a higher friction coefficient takes place. This is due to a change in nature of the third body in the contact, which consists exclusively of a compacted layer of surface oxidized metal particles above the critical pressure, but transforms into a mix of fully oxidized material and metal particles below the critical pressure. After the critical contact pressure is reached, a quasi steady state exists between the formation and ejection of third body material.

Acknowledgments The authors acknowledge the Swiss Confederation’s Innovation Promotion Agency (CTI) for financial support and Brugg Kabel AG (Switzerland) for their collaboration.

References [1] Rybiak R, Fouvry S, Bonnet B. Fretting wear of stainless steels under variable temperature conditions: introduction of a ’composite’ wear law. Wear 2010;268:413–23. [2] Fouvry S, Paulin C, Liskiewicz T. Application of an energy wear approach to quantify fretting contact durability: introduction of a wear energy capacity concept. Tribol Int 2007;40:1428–40. [3] Vieira AC, Ribeiro AR, Rocha LA, Celis JP. Influence of pH and corrosion inhibitors on the tribocorrosion of titanium in artificial saliva. Wear 2006;261:994–1001. [4] Soderberg S, Bryggman U, McCullough T. Frequency effects in fretting wear. Wear 1986;110:19–34. [5] Pasanen A, Lehtovaara A, Rabb R, Riihimaki P. Friction behavior of quenched and tempered steel in partial and gross slip conditions in fretting point contact. Wear 2009;267:2200–7. [6] Zhang X, Zhang C, Zhu C. Slip amplitude effects and microstructural characteristics of surface layers in fretting wear of carbon steel. Wear 1989;134:297–309. [7] Vingsbo O, Schon J. Gross slip criteria in fretting. Wear 1993;162–164: 347–56. [8] Vingsbo O, Soderberg S. On fretting maps. Wear 1988;126:131–47. [9] Kayaba T, Iwabuchi A. Effect of the hardness of hardened steels and the action of oxides on fretting wear. Wear 1981;66:27–41.

1460

N. Diomidis, S. Mischler / Tribology International 44 (2011) 1452–1460

[10] Berthier Y, Vincent L, Godet M. Fretting fatigue and fretting wear. Tribol Int 1989;22:235–42. [11] Verenberg M, Halperin G, Etsion I. Different aspects of the role of wear debris in fretting wear. Wear 2002;252:902–10. [12] Ramesh R, Gnanamoorthy R. Effect of hardness on fretting wear behaviour of structural steel, En 24, against bearing steel, En 31. Mater Des 2007;28: 1447–52. [13] Blanchard P, Colombie C, Pellerin V, Fayeulle S, Vincent L. Material effects in fretting wear: application to iron, titanium, and alumium alloys. Metall Trans A 1991;22A:1535–44. [14] Warburton J. The fretting of mild steel in air. Wear 1989;131:365–86. [15] Sherrington I, Hayhurst P. Simultaneous observation of the evolution of debris density and friction coefficient in dry sliding steel contacts. Wear 2001;249:182–7. [16] Mischler S, Barril S, Landolt D. Fretting corrosion behaviour of Ti–6Al–4V/ PMMA contact in simulated body fluid. Tribology 2009;3:16–23.

[17] Barril S, Debaud N, Mischler S, Landolt D. A tribo-electrochemical apparatus for in vitro investigation of fretting-corrosion of metallic implant materials. Wear 2002;252:744–54. [18] Brizmer V, Kligerman Y, Etsion I. The effect of contact conditions and material properties on the elasticity terminus of a spherical contact. Int J Solids Struct 2006;43:5736–49. [19] Fouvry S, Kapsa Ph, Zahouani H, Vincent L. Wear analysis in fretting of hard coatings through a dissipated energy concept. Wear 1997;203–204:393–403. [20] Mischler S, Mathieu HJ, Landolt D. Investigation of a passive film on an iron– chromium alloy by AES and XPS. Surf Interface Anal 1988;11:182–8. [21] Xianglin D. The effect of quench hardening on the fretting wear of medium carbon steel. Wear 1988;123:77–85. [22] Archard JF. Contact and rubbing of flat surface. J Appl Phys 1953;24:981–8. [23] Ovcharenko A, Etsion I. Junction growth and energy dissipation at the very early stage of elastic–plastic spherical contact fretting. J Tribol—Trans ASME 2009;131:1–8.