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Xu2002-CoatingWear-ThirdBody.pdf
JMEPEG (2002) 11:288-293
©ASM International
The Effect of the Third Body on the
Fretting Wear Behavior of Coatings
Gui-Zhen Xu, Jia-Jun Liu, and Zhong-Rong Zhou
(Submitted 28 December 2001; in revised form 20 February 2002)
The formation, oxidation, and agglomeration of wear debris of coatings were investigated in this study. The
rheology of the third body and its influence on the fretting wear behavior were studied in depth and
systemically. The results showed that the shape and nature of the debris were the essential factors determining the mobility of the third body. All factors that could make the debris layer or third body remain
on the contact surfaces would decrease the friction coefficient and fretting wear. The soft and large
plate-like debris particles were apt to remain in the contact region. Conversely, the hard and sphereshaped debris particles tended to be squeezed from the contact surfaces and to increase the fretting wear.
Keywords
fretting wear behavior, rheology, third body
1. Introduction
Fretting damage is a very complex phenomenon, which involves adhesion, abrasion, fatigue, and corrosion on the contact
surfaces. Under different conditions, it can be exhibited as
fretting fatigue, fretting wear, and fretting corrosion.[1,2] Compared with ordinary sliding wear, one of the important tribological characteristics of fretting wear is the effect of the wear
debris trapped on contact surfaces on the fretting process.[3]
Studies on the effect of debris on fretting wear have been
reported and discussed in the literature.[4-9] Iwabuchi[10] found
that the compacted oxide on a softer surface prevented the wear
of the oxide and abraded a harder opposing surface. The research conducted by Colombie[11] proved the beneficial effect
of the compacted oxide layer by its quick formation when
oxide particles or chalk powder were supplied artificially. Iwabuchi[12] also found that the loose oxide wear particles and
surface oxide film formed in the preheating had no significant
effect on the wear process; instead, the most important factor
was the formation of the compacted oxide layer on the surface.
Such an oxide layer was called “the third body” and had a good
load-carrying capacity to prevent metal-metal contact.[13] The
complexity of the fretting wear process originated mainly from
the influence of the formation and evolution of the third body
on fretting wear. The formation of the third body resulted from
the adhesion and transfer of first bodies and the ploughing of
asperities.[14] Strictly speaking, the loose debris particles coming from adhesion, transfer, and degradation of materials in the
initiation of fretting wear should not be regarded as the third
body. Indeed, the third body is the debris bed comprising comGui-Zhen Xu and Jia-Jun Liu, Dept. of Mechanical Engineering,
Tsinghua University, Beijing 100084, People’s Republic of China; and
Zhong-Rong Zhou, Tribology Research Institute, Southwest Jiaotong
University, Chengdu 610031, People’s Republic of China. Contact
e-mail: [email protected]
288—Volume 11(3) June 2002
pacted oxide particles, which could separate the rubbing surfaces and decrease the friction coefficient and wear. The formation of the third body implies that fretting wear reaches the
steady stage, when the rheology of the third body will determine the wear behavior of the later fretting process. This study
attempted to investigate the formation of the third body of
coatings based on the analysis of production, oxidation, and
agglomeration of wear debris. The influence of rheology on the
fretting wear behavior was then examined in depth and systemically.
2. Experimental Detail
2.1 Substrate Materials and Surface Modification
Techniques
The substrate material chosen for applying the surface
modification was 1045 steel. First, samples with the dimensions of 10 × 10 × 20 mm3 were machined from the 1045 steel
rod. Then the samples were heat treated at 860 °C for 20 min,
water quenched, and tempered at 600 °C for 30 min. Subsequently, the samples were ground and lapped with diamond
paste to Ra ⳱ 0.07 ␮m.
The surface modification coatings investigated here included: shot peening and ion sulfuration (PS duplex), ion plating TiN, and RF sputtering MoS2. The ion sulfuration coating
with the thickness of 10 ␮m was obtained using lowtemperature sulfuration equipment at 180 °C for 2 h. The shotpeening process was conducted with the Almen intensity
strength of 0.25 Amm, and ␾0.6 mm steel balls. TiN coating
with the thickness of 2.5 ␮m was deposited on 1045 steel
substrate in an ion-plating device (model MIP-800, Mechanics
Research Institute, Beijing, China) using a bias voltage of −100
to −150 V and a nitrogen atmosphere of 6 × 10−1Pa. An MoS2
coating with the thickness of 2.5 ␮m was produced by the
radiofrequency (RF) sputtering process. Before deposition, the
target, which was compacted using pure MoS2 powder (purity
ⱖ99 wt.%) with a small amount of LaF3, was RF-presputtered
and the substrate was ion-etched for 15 min at a dc power of
about 100 W in pure Ar gas (purity ⱖ 99.9%). The coatings
were deposited to a thickness of about 2.5 ␮m by RF sputtering
Journal of Materials Engineering and Performance
under the following conditions: anode voltage of 2.0 kV, substrate biased with a negative dc current of −100 V, and Ar
pressure of 5.3 Pa. Before surface modification, the substrates
must be ultrasonically cleaned in Analytical Reagent (AR)grade acetone.
The counterpart was a 52100 steel ball with diameter of 40
mm. The composition and main characteristics of the 1045 steel
substrate specimen and 52100 steel are listed in Tables 1 and 2.
2.2 Fretting Wear Tests and Analyses
Fretting wear tests were conducted on a tensioncompression hydraulic machine.[11] The scheme of the fretting
testing machine is given in Fig. 1. The coated flat specimen
was stationary and the 52100 steel ball was vibrated with small
reciprocating amplitude. All specimens were cleaned in an ultrasonic bath of alcohol before tests. The fretting experiments
were conducted under unlubricated, ambient temperature of 18
± 3 °C and relative humidity of 60% ± 10%. Because the debris
detachment is the fretting damage mechanism in the gross slip
regime, the experimental parameters were determined as normal load 300 N, slip amplitude 60 ␮m, and frequency 5 Hz.
After tests, the wear debris stuck on the stationary specimens
was collected using gummed tape. Then the morphologies and
Table 1
1045 Steel
52100 Steel
Table 2
1045 Steel
52100 Steel
composition of fretting wear scars and wear debris were examined by scanning electron microscope (SEM) with energy
dispersive spectroscopy (EDX).
3. Results and Discussion
3.1 The Formation of the Third Body of the Coatings
The variation of friction coefficient of PS duplex, ion-plated
TiN, and RF-sputtered MoS2 coatings with the number of
cycles are shown in Fig. 2. The time necessary to form the third
body varied with the coatings. Except for MoS2 coating, PS
duplex coating and TiN coating had begun to transit to the
steady state when the third body formed around 10,000 cycles.
Figure 3 displays the morphologies of fretting wear scars of
PS duplex, TiN, and MoS2 coatings under the experimental conditions of normal load 300 N, amplitude 60 ␮m, frequency 5 Hz, and 10,000 cycles. The analysis indicated that
there existed a large amount of debris on the fretting wear
scars. The plate-like oxide debris was shown on the wear
scar of the PS duplex coating (Fig. 3a). A lower yield strength
and larger surface roughness of the PS coating led its wear
debris to be produced during the work hardening process. The
continuous formation, movement, oxidation, and fragmentation
The Chemical Composition of 1045 Steel Substrate and 52100 Steel Ball (wt.%)
C
Si
Mn
Cr
S
P
Ni
0.45
0.95
0.27
0.25
0.65
0.30
0.25
1.50
0.02
0.02
0.04
0.04
0.25
0.20
The Main Characters of 1045 Steel Substrate and 52100 Steel Ball
E (GPa)
␴s (MPa)
␴b (MPa)
Hardness
(HRC)
Surface
Roughness
210
210
650 to 750
1700
850 to 900
2000
25 to 29
60 to 63
Ra ⳱ 0.07 ␮m
Ra ⳱ 0.02 ␮m
Fig. 1 The scheme of the fretting testing machine
Journal of Materials Engineering and Performance
Fig. 2 The variation of friction coefficient of shot peening and ion
sulfuration duplex (PS), TiN, and MoS2 coatings with number of
cycles (normal load 300 N, amplitude 60 ␮m, and frequency 5 Hz)
Volume 11(3) June 2002—289
heap of materials, which probably came from the compacted
debris and transferred material of the counterpart. During
the fretting wear, plastic deformation and fracture frequently
occurred on this thick debris layer comprising Ti, Fe, and
Cr oxides. At the same time, the loose debris particles oxidized
severely on the contact surface and became more brittle and
smaller. The morphology of the fretting wear scar of the
MoS2 coating (Fig. 3c) shows that a lot of MoS2 debris
transferred from the coating to the counterpart was smeared
on the coating undegraded. Obviously the third body composed
of MoS2 debris played an effective lubricating role. This
not only kept the friction coefficient at a low level throughout the process, but also minimized the damage to the substrate.
3.2 The Effect of Rheology of the Third Body on the
Fretting Wear Behavior of the Coatings
Fig. 3 The morphologies of fretting wear scars of the coatings (normal load 300 N, amplitude 60 ␮m, frequency 5 Hz, and 10,000
cycles): (a) PS composite coating, (b) TiN coating, and (c) MoS2
coating
of a lot of debris particles resulted in the formation of a
debris bed or third body composed of iron oxides. The morphology of wear scar of TiN coating (Fig. 3b) shows the
290—Volume 11(3) June 2002
The formation of the third body was a virtual process, in
which the loose debris particles produced by various damage
mechanisms were trapped, compacted, deformed, oxidized,
broken, and aggregated continuously and alternatively on
the contact surfaces. After the formation of the third body,
the reciprocating movement of fretting wear still kept it
moving and evolving. Therefore, the nature and rheology of the
third body affected the wear behavior of the whole fretting
wear system.
The morphologies of the debris eliminated from the contact
surface of PS duplex coating at 10,000 and 100,000 cycles,
respectively, are shown in Fig. 4. Analysis indicated that the
fine plate-like debris (d ≈ 50 nm) had aggregated to larger
lumps (d ≈ 1 ␮m) (Fig. 4a) at 10,000 cycles. The debris bed of
steady state (100,000 cycles) comprised finer sphere-like particles (d ≈ 30 nm) (Fig. 4b), which were Fe oxides according to
the EDX analysis (Fig. 5). The variation of debris shape of the
PS duplex coating from plate to sphere greatly improved the
mobility of the third body. This promoted the delamination of
the substrate and brought the friction coefficient of the PS
duplex coating to a higher level than that of the other coatings
at steady state.
Figure 6 shows the morphologies of debris squeezed from
the contact surface of TiN coating at 10,000 and 100,000
cycles, respectively. It can be seen that the debris of both
10,000 and 100,000 cycles looked like fine plate-like aggregation. However, the particles of 100,000 cycles (d < 50 nm) (Fig.
6b) were smaller than that of 10,000 cycles (d > 50 nm) (Fig.
6a), and the former seemed looser than the latter. It was possible that the debris eliminated earlier included part of the
TiO2, which adhered the other oxides to form the large aggregation, and they were not fragmented completely because of
the short period they remained on the contact surface. At steady
stage, a large amount of the substrate debris composed mainly
of incompletely oxidized metal particles was eliminated from
the contact area, which made the debris look loose. EDX analysis of the debris at 100,000 cycles (Fig. 7) indicated that the
content of Ti in the debris squeezed out of the contact surface
was smaller than that of the debris remaining on the wear scar
(Fig. 8). Results suggested that TiO2 was apt to stay in the
interface. TiO2 was also beneficial for forming the third body
Journal of Materials Engineering and Performance
Fig. 4 The morphologies of the wear debris of the PS composite
coating at different stages: (a) 10,000 cycles, and (b) 100,000 cycles
Fig. 6 The morphologies of the wear debris of the TiN coating at
different stages: (a) 10,000 cycles, and (b) 100,000 cycles
Fig. 5 The EDX analysis of the wear debris of the PS composite coating at 100,000 cycles
and decreasing the friction coefficient of TiN coating at steady
stage of fretting wear.
The morphology and composition of the debris eliminated
Journal of Materials Engineering and Performance
from the contact surface of MoS2 coating at 100,000 cycles are
shown in Fig. 9. It showed clearly that the debris of the MoS2
coating were large plate-like particles composed of MoS2 and
Volume 11(3) June 2002—291
MoO3, which still played a marked lubricating role. In addition,
MoS2 debris existing as large plates remained more easily in
the interface to form the third body, the good load carrying
capacity of which effectively restrained the damage of the substrate and kept the friction coefficient of the MoS2 coating at a
low level until the end of the fretting experiment.
On the basis of these analyses, it can be summarized that the
third body, which is apt to remain on the contact surface or
cling to the first bodies, can restrain the fretting wear from
progressing because of the lubricating effects and separation of
counterparts. Conversely, the wear debris that is eliminated
from the contact surface will increase the fretting wear by its
abrasion. The nature and rheology of the third body are mostly
affected by the properties of materials and environmental conditions. Under the same environmental conditions, the mechanical and physicochemical properties of first-body materials
and contact regime are the essential factors determining the
formation and evolution of the third body.
4. Conclusions
•
•
•
The third body of the PS duplex coating comprised Fe
oxides. TiO2, transferred material of the counterpart, and
the substrate debris made up of the third body of TiN
coating. The third body of the MoS2 coating presented
itself by MoS2 debris smearing on the coating.
The formation and rheology of the third body determined
the fretting wear behavior of the coatings at steady stage.
All the factors that made the debris layer or third body
remain on the contact surface were able to decrease the
friction coefficient and fretting wear. Conversely, the fretting wear resistance would be lowered if the debris particles were easily eliminated from the contact surfaces.
The shape and nature of the debris were the essential factors to determine the mobility of the third body. The soft
and large plate-like debris particles were apt to remain in
the contact region. In contrast, the hard and sphere-shaped
Fig. 7 The EDX analysis of the wear debris of the TiN coating at 100,000 cycles
Fig. 8 The morphology and composition of the debris layer on the contact surface of the TiN coating. (a) The morphology of the debris layer on
the contact surface of the TiN coating, and (b) the EDX analysis of the debris layer
292—Volume 11(3) June 2002
Journal of Materials Engineering and Performance
Fig. 9 The morphology and composition of the wear debris of the MoS2 coating. (a) The morphology of the wear debris of the MoS2 coating, and
(b) the EDX analysis of the wear debris
debris particles tended to squeeze from the contact surfaces and increased the fretting wear.
Acknowledgment
The authors would like to thank the National Natural Science Foundation (Project Number 59725513) for the financial
support to this research.
References
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1972.
2. R.B. Waterhouse: Fretting Fatigue, Applied Science, London, 1981.
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Beijing, 1992, pp. 134-67 (in Chinese).
4. P.L. Hurricks: “The Mechanism of Fretting—A Review,” Wear, 1970,
15, pp. 389-409.
5. R.E. Pendlebury: “Formation, Readhesion and Escape of Wear Particles in Fretting and Sliding Wear in Inert and Oxidizing Environments,” Wear, 1988, 125, pp. 3-23.
6. A. Iwabuchi: “The Role of Oxide Particles in the Fretting Wear of
Mild Steel,” Wear, 1991, 151, pp. 301-11.
Journal of Materials Engineering and Performance
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10. T. Kayaba and A. Iwabuchi: “Effects of the Hardness of Hardened
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11. C. Colombie, Y. Berthier, A. Floquet, and L. Vincent: “Fretting: Load
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12. A. Iwabuchi, K. Hori, and H. Kudo: “The Effects of Temperature,
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Mild Wear for S45C Carbon Steel and SUS304 Stainless Steel” in
Proceedings of the International Conference on Wear of Materials,
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13. M. Godet: “The Third-Body Approach: A Mechanical View of Wear,”
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pp. 223-45 (in Chinese).
Volume 11(3) June 2002—293
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