2
JTEKT Engineering Journal No. 1006 (2009)
20
Study of Tribology in the Past Twenty Years
Fundamentals and Applications
The representative research results in the past 20 years at my
laboratory are introduced as follows,(1)Static friction coeffi
cient changes by the shape of contact area.(2)Different wear modes
are classifi ed in one diagram as Wear Map by introducing indexes
of severity of
contact.(3)Repeated sliding friction at self-mated SiC and Si3N4
in water generates friction coeffi cient below 0.01.
Micro texture on contact surfaces generates friction coeffi
cient in the order of 0.0001.(4)Tribocoating of indium on the
surface of SUS440C disk generates friction coefficient below
0.05
against Si3N4 pin in high vacuum.(5)N2 gas supply at the
contacts of Si3N4/CNx and CNx/CNx in air generate friction coeffi
cient in the order
of 0.001.(6)Tribolayer formed by tribo-chemical reaction changes
friction and wear drastically.
Key Words: micro-slip, wear map, water lubrication,
tribo-coating, N2-gas lubrication, tribolayer
1
TribosTribology
20
2
2.1(a)W
Prof. Koji KATO
FF d l F/Wl
lls
0.85(b) 2
ls 0.69
4
ls 0.32
20
3JTEKT Engineering Journal No. 1006 (2009)
W=7.85N
0.60.50.40.30.20.100 0.1 0.2 0.3 0.50.4
F
FW
W
F
l(=/) ls0.85()
dmm
F
F
F
ls0.49()ls0.48()
ls0.32()
dx
x
1
The effect of shape of contact area on micro-slip andstatic
friction coefficient
l0.29l0.29l0.30l0.29
2mm 2mm 2mm 2mm
2.2Wear Map
Type1Mode
Cutting modeWedge modePloughing mode 3 Dp f 2
(b)0.6
0.5
0.4
0.3
0.2
0.1
0
1.00.80.60.40.20f
l() =
(a)SEM
(Cutting)
(Wedge forming)
(Ploughing)
: W: F: H: R: a: h
DP = =R H2W
12
Rp p 2H2W 1
f
Dp
DP = =R H2W
12
Rp p 2H2W 1
2
Abrasive wear map of metals
ha
ha
F
FW
F
W
=l
l
x,d
W
F
W =7.85N
ls= 0.85
(a)
F
W(b)
ls= 0.69
1
Micro-slip in contact area corresponding to the increasein
friction force and the static friction coefficient
l0.22 l0.85l0.70l0.502mm2mm2mm2mm
l0.30l0.172mm2mm
l0.69l0.482mm2mm
20
4 JTEKT Engineering Journal No. 1006 (2009)
l Pmaxd KIc
c v W Hv
DTs
DTs
k q c
ScSeverity of Contact
vHWVkqcSc,t= ( )
cl
KIC
Sc,m= ( )
(110l)Pmaxd
20
15
10
5
0103 102 101 100
3
Wear map of ceramics describing mild and severe wear
(a3)
Es
Hs
Ys
(b)
(c)
4
7
6
5
4
3
21
7
6
5
4
3
21
Hf/Hs
Yf/Ys
3210
(d)
(a2)
Ef/Es2l0.25
/ t/a
45
Wear map of delamination of hard coatings
(a1)
20m
4m
2m
4
3
2
1
0
Z/a
0.00 1.601.200.800.40
wrvm/Pmax
l0.70l0.50l0.25
t/a0.5X/a0.0Ef/Es2.0
2 Scm Sct
3
2.3
SEM1.6 104 1
DDx
R101 /pass
20
5JTEKT Engineering Journal No. 1006 (2009)
10
0
20
2 4 6 8 (104)Passage Number of Ball
(Passes)
Amount of Plastic FlowDDx (m)
Relation between surface flow, number of friction passes and
contact pressure
6.0Mpa26.5Mpa45.1Mpa63.5Mpa
20mIndentation
0.52m/s
2.5
0
5.0
20 40 60 80 100
104
Contact pressure (MPa)
Flow RateR (m/Pass)
20mIndentation
Rough Surface(4m Rmax)
RxRy
R0.52m/s
10
The relationship between surface flow rate andcontact
pressure
3
3.111 SiC Si3N4
10nm 0.0112
Si3N4 6H2O 3SiO2 4NH3SiC 2H2O SiO2 CH4SiO2 2H2O Si(OH)4
104 l 0.15
S10C (0.1 wt.% C
steel)Rmax4mPm9.8MPaV0.52m/sAlkylnaphtalene(2835 at cst 38)
Flow wear
(a) (b)
(c) (d)
FrictionalDirection
1.6103 Passes 8103 Passes
1.6104 Passes 4.8104 Passes
6
Generation process of a flow wear particle of steel byrepeated
friction
0.25m/s; 26.5MPa
3.2104 Passes 0Pass 4.8104 PassesFrictional Direction
10m(a) (b) (c)
Simulation of flow wear process by the change ofVickers
indentation mark in repeated friction
S10C (0.1 wt.% C steel)Alkylnaphtalene (2835 cst at 38)
Rmax0.4mPm9.8MPaV0.52m/s
(a) (b)
SEM6
SEM images of flow wear particles of steel generated in oil
20
6 JTEKT Engineering Journal No. 1006 (2009)
14121086420
1.2
1.0
0.8
0.6
0.4
0.2
0
Sliding contact in waterLoad5NSliding velocity120mm/s
Frictioncoefficientl
l< 0.01
Water
Sliding cycles N104 cycles
SiC / SiC
Si3N4 / Si3N4
SiC / SiCSi3N4 / Si3N4
11SiC/SiCSi3N4/Si3N4
Reduction in friction coefficient of SiC/SiC and Si3N4/Si3N4 by
repeated friction in water
Si3N4 Pin/Si3N4 DiskSliding in waterLoad W5N
Sliding Velocity v120mm/sSliding cycles N87 500 cycles
12Si3N4Si3N4
Smooth wear surfaces on Si3N4 pin and Si3N4 diskformed by
repeated friction in water
3.2
13 SiC
14
Wc15Wc h/ d rWcoWcWc/Wco 2.0 2.5h/d 0.01 0.02r 516
1718 l
Wc17 l 0.0001
20mm
13SiC10
Micro-pits formed on SiC disk surfacePit diameter: 150mPit depth
: 34m
WcWcWcoWc
0
0.01
0.02
0.03
0.04
Friction coefficient l
SiC/SiCRotational speed n1 200min1LubricantPurified waterSupply
rate60ml/min
0 500 1 000 1 500Load WN
2 000 2 500 3 000 3 500
14Wc10
The effect of size and area ratio of micro-pits on critical
seizure load
Untexturedu150, 2.8%, Depth 3-4mu150, 22.5%, Depth 3-4mu350,
4.9%, Depth 3-4m
20
7JTEKT Engineering Journal No. 1006 (2009)
4
19
20
21
104
Si3N4 SUS440C22 SUS440C In TEM 400nm23 EDX SiCrOIn24 TEM In
SiC (CIP)
35040RSPCLP
3.4-82.7-7.92.6-7
7.74.94.0
Lower specimenUpper specimen10mm
100m 500m
Material
Textures name
Pit diameterd (m)
Pit depthh (m)
Pit area ratior (%)
SiC (CIP) SiC (CIP)
RSP(RectangularSmall Pit)
CLP(Circular Large Pit)
CLRSP(Circular Large
and Rectangular Small Pit)
350 40
500m
16SiC11
Three pit patterns formed on SiC disk surface
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
CLRSPCLPRSPNo texture
Stable friction coefficient
s Lubricantrefined waterSupply rate60ml/minTemperature14-20
*Under detection limit
173SiC/SiC11
The effect of three pit patterns on friction coefficients
ofSiC/SiC in water
0
1 000
2 000
3 000
4 000
5 000
CLRSPCLPRSPNo texture
Critical load WcN
Lubricantrefined waterSupply rate60ml/minTemperature14-20
183SiC/SiCWc11
The effect of three pit patterns on critical seizure loadWc of
SiC/SiC in water
2.02.51.52.01.01.50.51.0
Wc/Wco
0
0.01
0.02
0.03
0.04
0 5 10 15 20 25
Depth-diameter ratio / d
h
rPit area ratio %
SiC cylinder/SiC diskPit diameter d50-650mPit depth
h1.916.6mLubricantPurified water
15h/dr(%)Wc/WcoWco10
The relationship among depth/diameter ratio h/d andarea ratio
r(%) of pits on disc surface and the normalizedcritical seizure
load Wc/Wco
20
8 JTEKT Engineering Journal No. 1006 (2009)
Tribo-coating process Friction test
Load
(1min) (12min) 104106 (10 cycles)
19Tribo-coating12
Friction assisted coating lubrication (Tribo-coating):
Vapor-deposition of soft metal In for a few minutes justbefore and
after initiation of sliding
0 21 30
0.2.
0.4
0.6
0.8
1
Number of cycles104 cycles
Pin/DiskSi3N4/
SUS440cLubricantInH2nm/minth1-2minP1.3GPav24mm/sVR106Pa
Evaporation
Friction coefficientl
2012
The effect of interval tribo-coating
0
0.1
0.2
0.3
1050 15
Friction coefficientl
Number of cycles103 cycles
Range of friction coefficientobtained with soft metal films
Pin/DiskSi3N4/SUS440CP1GPav22mm/secVR106Pa In
(Tribo-coating)
In (Vapor deposition)Ag (Ion-plating)Pb (Ion-plating)
2113
The lower friction and longer life of Tribo-coating film
incomparison with films by vapor-deposition and ion plating
Carbon film (overcoat)
Tribo-layer
Si3N4 pin
(a) (b)
22InSiTEM14
TEM image of tribo-layer on Si disk surface formed
bytribo-coating of In
100nm 10nm
(a)
(b)
Counta.u.
Counta.u.
In
In
Cr
Cr
Cr
Cr
CuFe
Fe
Si
Si
O
O
0 1 2 3 4 5 6 7 8 9 10X-ray EnergykeV
0 1 2 3 4 5 6 7 8 9 10X-ray EnergykeV
23SiEDX14
Compositions in tribo-layer on Si disk surface analyzedby
EDX
(b)22(b)Black points in Fig. 22(b)
(a)22(a)Matrix in Fig. 22(a)
(b)Matrix
(a)Nano-particle
24TEM14
TEM image of tribo-layer
2.5nm
20
9JTEKT Engineering Journal No. 1006 (2009)
0.00.20.40.60.81.0
10 0001 000100Number of cycles N,
x103 cycles
101
N2 at 50th cycle
O2
Friction
coefficientl
Load1NSliding speed0.21-0.27m/sTemperature20-24HumidityRH
20-40%
100m 100m
10 cycles 10 000 cycles
l= 0.005
28CNx/CNxO250N217
The change in friction coefficient of CNx/CNx bysupplying N2 gas
after initial 50 cycles in O2 gas
5N2
Si3N4 CNx25267N2 0.0127 0.7 N2 0.02
dry airO2 dry airO2 50 100 N2ws28 O2 50 CNx/CNxN2l 0.00529lwsl
0.05l 5 10 8mm3/Nm
0
0.1
0.2
0.3
0.4
0.5
0.16
0.36
0.030.0090.05
VacuumAir N2 CO2 O2
PinSi3N4 ball (r4.0mm)Disk100nm CNx/SiNormal load100mNMaximum
contact pressure200MPaSliding speed4mm/s
Si3N4
Si3N4CNx
(1x105 Pa) (2x104 Pa) (7.4x104 Pa) (7.4x104 Pa) (7.4x104 Pa)
Friction coefficientl
25Si3N4/CNx15
The effect of gas environment on friction of Si3N4/CNx
0
0.1
0.2
0.3
0.4
0.5
N2VacuumAir ArHe
(4x103 Pa) (1.0x105 Pa)
0.35
0.14
0.01
0.20
0.31
Friction coefficientl
Disk100nm CNx/SiPinSi3N4 ball (r4.0mm)Normal
load750mNPmax400MPaV0.26m/s
(1.0x105 Pa)
26Si3N4/CNx16
The effect of gas environment on friction of Si3N4/CNx
0.0
0.2
0.4
0.6
0.8
1.0
14121086Number of cycles103 cycles
420
0L/min 1.2L/min 4.8L/minN2 N2Air
DiskCNx (100nm)/Si3N4PinSi3N4 ball (r4mm)Normal load200mNRotary
speed250min1 (0.4m/s)
Friction coefficientl
Air
27Si3N4/CNxN216
The effect of blowing N2 gas to the contact on frictionof
Si3N4/CNx in air
20
10 JTEKT Engineering Journal No. 1006 (2009)
012345
0
Air O2 N2 O2 N2Air N2From1st cycle
From1st cycle
Load1NSliding speed0.21-0.27m/s
(250min1)Temperature20-24HumidityRH 20-40%Gas flow rate2.0L/min.
(2.10cc/mm2s)Inner radius of tube4.5mm
Steady state
friction coefficientl
Specific wear amount
Wsx10
7 mm3 /Nm
0.1
0.2
0.3
100 cycles(400mN)
50 cycles
29CNx/CNxdry airO2N2lws(mm3/Nm)17
The values of friction coefficient l and wear ratio ws (mm3/Nm)
at CNx/CNx in dry air, O2, N2 and combination of gases
6
ZDDPZinc Dialkyl Dithio Phosphate 60
ZDDP PAOPoly-Alpha Phosphate30
31TEM 200nm ZnFePCSOCr31 EDX 200nm
Steel Cylinder
TEM Analysis
LoadWear Track
Plate(1082mm)Lubricant1%ZDDPin PAO (80)
7 mm stroke@7 Hz
Cylinder (66mm,bearing steel)
Iron Oxide Plate
R-O S S O-R
S SP P
R-O O-R R:-CH-CH2-CH-CH3CH3
CH3
ZDDP : 4-methyl-2-pentanol
Zn
1.0mm
l
0 1 000 2 000 3 000
0.20
0.15
0.10
0.05
0.00
Timesec.
30ZDDPPAO18
Out look of surface layer on oxidized steel plate formed by
friction against steel cylinder in oil (PAO) containing ZDDP
Upper Layer
Middle Layer
Bottom Layer
Tribofilm
R-O S S O-RS SP P
R-O O-R R:-CH-CH2-CH-CH3CH3
CH3
ZDDP : 4-methyl-2-pentanol
Zn
40nm
Iron Oxide Layer
TEM Cross Section PhotographNear the Surface
Carbon Layer(For protection)
31400nmTEMEDX Depth Profile18
TEM image of tribo-layer (400nm) on friction surface of steel
plate and depth profiles of elements by EDX
20
11JTEKT Engineering Journal No. 1006 (2009)
1
2Si3N4SiCSi3N4tribo-chemical wear
(Si3N4)
7.7mm 7.1mm1.0m 0.01m500m 0.14m
180min
Si3N4 Si3N4
34Magnetic fluid grinding of ceramic balls
34 Si3N4 40 100
1990
Si3N4 2223
35
Si3N4 SUS440C /
121314
7
32 1995
Shrink-Fitter 100
19
33
X-Y 2000
2021
100
32/Laser microscope using shrink fitter forceramicspolymer/metal
shrink fitting
XY Stage driven by Ultrasonic Motorfor LSI of 0.15m line
width
Electron BeamLithography System
X-Y stage
33X-Y
Totally ceramic X-Y stage driven by ultrasonic wave forelectron
beam lithography
20
12 JTEKT Engineering Journal No. 1006 (2009)
In
Pt heater Au wire
Membrane area Siwafer
SiO2
5mm
35In
A ball bearing with micro-evaporators of In for space
application
8
35 20 25 20
21
Si3N4 SiCSi3N4/SUS440C InSi3N4/CNX N2 15
J. Liu, K. Oba, K. Kato and H. Inooka: Partial Slip Visual izat
ion at Contact Surface with the Correlation Method, Visualization
Society of Japan, 15199547-53.
K. Hokkirigawa and K. Kato: Abrasive Wear Diagram, Proceedings
of Eurotrib85, 419851-5.
K. Adachi, K. Kato and N. Chen: Wear Map of Ceramics, Wear
203/2041997291-301.
D. F. Diao, K. Kato and K. Hayashi: The Local Yield Map of Hard
Coating under Sliding Contact, Thin Films in Tribology: Proceedings
of the 19th Leeds-Lyon Symposium on Tribology, Leeds, UK, 1991, D.
Dowson et al. Editors, Tribology Series, 251992Elsevier,
419-427.
K. Kato: Microwear Mechanisms of Coatings, Surface and Coating
Technology, 76-771995, 469-474.
T. Akagaki and K. Kato: Plastic Flow Process of Surface Layers
in Flow Wear under Boundary Lubricated Conditions, Wear, 1171987,
179-196.
T. Akagaki and K. Kato: Simulation of Flow Wear in Boundary Lubr
icat ion Us ing a Vickers Indentation Method, STLE Tribology
Transactions, 311988, 311-316.
M. Chen, K. Kato and K. Adachi: The Diff erence in Running-in
Period and Friction Coeffi cient between Self-mated Si3N4 and SiC
under Water Lubrication, Tribology Letters, 112001, 23-28.
20
13JTEKT Engineering Journal No. 1006 (2009)
M. Chen, K. Adachi and K. Kato: Friction and Wear of Self-mated
SiC and Si3N4 Sliding in Water, Wear, 2502001, 246-255.
X. Wang, K. Kato, K. Adachi and K. Aizawa: Loads Carrying Map
for the Surface Texture Design of SiC Thrust Bearing Sliding in
Water, Tribology International, 362003, 189-197.
K. Adachi, K. Otsuka, X. Wang and K. Kato: Eff ects of Surface
Texture on Water Lubrication Properties of Advanced Ceramics,
Journal of the Japan Society for Abrasive Technology, 502006,
107-110.
K. Kato, H. Furuyama and M. Mizumoto: The Fundamental Properties
of Tribo-Coating Films in Ultra High Vacuum, Proceedings of the
Japan International Tribology Conference Nagoya, 1990, 11990,
261-266.
K. Adachi and K. Kato: Reliable Design of Space System in
Tribology Viewpoint, Proceedings of the 22nd International
Symposium on Space Technology and Science, 1,2000, 593-598.
K. Adachi and K. Kato: In-situ and On-demand Lubrication by
Tribo-coating for Space Applications, Journal of Engineering
Tribology, IMechE, to be published.
N. Umehara, M. Tatsuo and K. Kato: Nitrogen Lubricated Sliding
between CNx Coatings and Ceramic Balls, Proceedings of the
International Tribology Conference Nagasaki, 2000, 2,2001,
1007-1012.
K. Kato, N. Umehara and K. Adachi: Friction, Wear and
N2-lubrication of Carbon Nitride Coatings: a Review, Wear,
254,2003, 1062-1069
K. Adachi, T. Wakabayashi and K. Kato: The Eff ect of Sliding
History on the Steady State Friction Coeff icient between
CNx-coating Under N2 Lubrication, Proceedings of the 31st
Leeds-Lyon Symposium on Tribology, 2004, Leeds, UK, D. Dowson et
al.Editors, Tribology and Interface Engineering Series, 48,
Elsevier,2005, 673-677.
K. Ito, J. M. Martin, C. Minfray and K. Kato: Formation
Mechanism of a Low Friction ZDDP Tribofilm on Iron Oxide, STLE
Transactions, 50, 2007, 1-6.
I. Nitta, K. Kigoshi and K. Kato: Study of the Fitting Strength
between Ceramic and Metal Elements with the Use of a Shrink Fitter
at Elevated Temperature (Proposal of the Shrink-Fit Method with the
Use of a Shrink Fitter and Experimental Results), JSME
International Journal Series 3, 32
1989, 632-639. T. Honda and K. Kato: The Infl uence of
Ultrasonic Shape on Frict ion and Wear Properties in Ultrasonic
Drive, JaST, 411996, 178-184.
K . Adach i , K . Kato and Y . Sasatan i : The Micromechanism of
Friction Drive with Ultrasonic Wave, Wear, 1941996, 137-142.
N. Umehara and K. Kato: A Study on Magnetic Fluid Grinding1st
Report, the Effect of the Floating Pad on Removal Rate of Si3N4
BallsTransactions of the JSMEC, 541988, 1599-1604.
N. Umehara and K. Kato: Principles of Magnetic Flu id Gr ind ing
o f Ceramic Ba l l s , J . Appl . Electromagnetics in Materials,
11990, 37-43.
