Wear resistant and low friction
nanocomposite coatings
Dr Tomasz Suszko
http://www.balticnet-plasmatec.org
•
Lecture outline
Plasma sputtering – short description
•
•
DC-, triode-, RF-, magnetron sputtering
Nonreactive and reactive mode
•
Low friction nanocomposite coatings
•
Chosen results: Mo2N/Cu nancristaline films
– structure, mechanical and tribological
properties
•
•
Structure, hardness
Friction & wear mechanisms in temperature range
RT-400°C
International Student Summer School „Nanotechnologies in materials engineering”
Warsaw - Koszalin 2006
Tomasz Suszko
suszko@tu.koszalin.pl
2
http://www.balticnet-plasmatec.org
Plasma
- the 4th
state of matter
http://fusedweb.pppl.gov/CPEP
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suszko@tu.koszalin.pl
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Fundamentals of plasma sputtering
– DC sputtering (diode sputtering)
http://www.balticnet-plasmatec.org
Disadvantages:
• Low ion current density
(low sputtering rate)
Cathode
Voltage
~1.5 kV
• Electron
emission
+
• Sputtering
10
1
0.1
0.01
10
100
1000
Electron energy [eV]
• Implantation
• High working gas pressure
resulting in scattering (low
deposition rate)
• Defects
generation
• E-m radiation
Ionisation coeffcient
Pressure
~10 Pa
noble gas
(e.g. Ar)
Anode
+ substrate
• Dielectric materials can not
be sputtered
• High voltage is needed
International Student Summer School „Nanotechnologies in materials engineering”
Warsaw - Koszalin 2006
Tomasz Suszko
suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
Fundamentals of plasma sputtering
– triode sputtering
+ Lower working gas pressure
– 0.1 Pa (higher deposition
rate)
+ 100 V
Substrate
Target
+ Higher ion current density
(higher sputtering rate)
Ionisation coeffcient
+
0.5 kV
-
10
1
0.1
0.01
10
1000
Electron energy [eV]
– Dielectric materials can
not be sputtered
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Tomasz Suszko
suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
Fundamentals of plasma sputtering –
microwave assisted sputtering
+ Lower working gas pressure
– 0.1 Pa (higher deposition
rate)
Microwave antenna
+
–
Substrate
Target
0.5 kV
Ionisation coeffcient
+ Higher ion current density
(higher sputtering rate)
10
1
0.1
0.01
10
100
1000
Electron energy [eV]
– Dielectric materials can
not be sputtered
International Student Summer School „Nanotechnologies in materials engineering”
Warsaw - Koszalin 2006
Tomasz Suszko
suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
Fundamentals of plasma sputtering – RF
sputtering
Matchbox
The differce in:
• mobility of
electrons and ions
• areas of electrodes
results in
negative target
selfbias
thus,
RF
dielectric materials
can be sputtered
Substrate
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Tomasz Suszko
suszko@tu.koszalin.pl
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Fundamentals of plasma sputtering –
motion of the electron in electromagnetic
field
http://www.balticnet-plasmatec.org
v e cos a
a
ve
ve sin a
ve
RL
ve cosa
a
ve cosa
RL 
ve
vR
vd
RL
E
B
cathode
eB
L 
me
International Student Summer School „Nanotechnologies in materials engineering”
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 sin a
L
Tomasz Suszko
suszko@tu.koszalin.pl
8
http://www.balticnet-plasmatec.org
International Student Summer School „Nanotechnologies in materials engineering”
Warsaw - Koszalin 2006
Tomasz Suszko
suszko@tu.koszalin.pl
9
http://www.balticnet-plasmatec.org
International Student Summer School „Nanotechnologies in materials engineering”
Warsaw - Koszalin 2006
Tomasz Suszko
suszko@tu.koszalin.pl
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Ionisation coeffcient
http://www.balticnet-plasmatec.org
Fundamentals of plasma sputtering
– magnetron sputtering
– unbalanced magnetron sputtering
10
+ Low working gas
pressure – 0.1 Pa
1
+ Very high ion current
density is possible (high
sputtering rate)
0.1
0.01
10
100
1000
Electron energy [eV]
Substrate
DC or pulsed
power supply
There is a possibility to control the
substrate ion current and the energy
of the ions as well
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suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
What materials can be sputtered and
deposited?
Whatever one need?
It must be kept in mind that:
• Compounds, targets are made of, are
decomposed to the atomic form and only then
can react again on the substrate (not always
getting appropriate conditions)
• Sputtered atoms are scattered along their way
towards substrate (the lighter the more intense
thus the stoichiometry can change)
• A sputtered compound can not to easily
evaporate (sufficient vacuum can not be obtain)
International Student Summer School „Nanotechnologies in materials engineering”
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Tomasz Suszko
suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
End of part one
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From yesterday
http://www.balticnet-plasmatec.org
•Mean free path
•Secondary electron emmision
•Ion implantation
•Sputtering
•Charging effect
•Thermoemission
•Magnetic mirror and trap
•Larmor frequency and radius
•Magnetron source (gun)
International Student Summer School „Nanotechnologies in materials engineering”
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Tomasz Suszko
suszko@tu.koszalin.pl
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Fundamentals of plasma sputtering –
reactive sputtering
http://www.balticnet-plasmatec.org
Compounds of the
target and gas elements
Inert gas (e.g. Ar)
Reactive gas (N2, O2, CH4 etc.)
Control unit
Optical signal
(optical emission spectroscopy)
For poorly conducting
or insulator deposits
pulsed power supply is
very usefull
•
•
•
•
Gas pressure
Gas flows
Discharge power
(Substrate bias –
energy of the ions)
• (Substrate ion
current density)
Pumping system
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What I won’t speak about is...
http://www.balticnet-plasmatec.org
•Plasma enhanced chemical vapour deposition
•Laser ablation
•Plasma spraying
•Ion implantation
(clasical or
plasma immersion)
•Plasma nitriding or
carburazing
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etc.
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suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
Working gases:
• Ar (inert gas),
• N2 (for nitrides),
• O2 (for oxides),
• CH4, C2H2 (for carbides and
DLC)
Plasma maintained by:
• DC or pulsed discharge
(magnetron),
• Vacuum arc, RF e-m waves
What we use
for deposition is...
Targets made of:
• Ti, Al, Mo, V, Ag, Cu
but also
• Fe, Ni, Co
and
• Si
International Student Summer School „Nanotechnologies in materials engineering”
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Tomasz Suszko
suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
What we develop for process control and
data acquisition is...
Valve unit
Gases
Optical signal
Coils supply
Spectrometer
Magnetron sources
Pulsed power
supply
Pulsed power
supply
Substrate
bias
and heating
Pumping system
International Student Summer School „Nanotechnologies in materials engineering”
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Tomasz Suszko
suszko@tu.koszalin.pl
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What we interest in is...
http://www.balticnet-plasmatec.org
F
L
Continuous looking for novel anti-wear coatings and
development of their deposition methods
Phenomena in the tribolgical contact between hard
coated surface and a counterpart
• Structure, elemental and phase composition of the coatings
in the initial state (after deposition)
• Stress, adhesion, hardness of the coatings
• Friction during tribological tests (especially in elevated
temperatures)
• Tribomutation - chemical and physical changes of the „third
body” – elemental and phase composition, structure etc. of
that
• The role of oxides in friction process
International Student Summer School „Nanotechnologies in materials engineering”
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Tomasz Suszko
suszko@tu.koszalin.pl
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Where can we look for hard compounds?
http://www.balticnet-plasmatec.org
International Student Summer School „Nanotechnologies in materials engineering”
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How to obtain hard films
http://www.balticnet-plasmatec.org
 Chemical sythesis
( DLC, c-BN, AlMgB, C3N4 )
 Forming proper physical microstructure
• Nitride or carbide multilayers
(TiN/CrN, TiN/TiAlN i in.)
• Composites
nc-MexN/a-Si3N4
nc-MexC/a-C:H
np. nc-TiN/a-Si3N4
• Composites
MexN/M
np. (ZrN/Cu, Cr2N/Cu, TiN/Ag)
International Student Summer School „Nanotechnologies in materials engineering”
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Tomasz Suszko
suszko@tu.koszalin.pl
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Hardness is not all - there is friction also!
http://www.balticnet-plasmatec.org
F A
A 
 



L
L
AH H
Soft
materials
F
A 
A
large
small
Shear strength
Hardness
 A 
small
Hard
materials
large
L
F
A
L
 Shear strength and hardness depend on each other
thus friction coefficients are comparable for various
izotropic materials.
International Student Summer School „Nanotechnologies in materials engineering”
Warsaw - Koszalin 2006
Tomasz Suszko
suszko@tu.koszalin.pl
22
Self-lubricating materials
http://www.balticnet-plasmatec.org
• As a result of rubbing, a thin low-shear-strengh layer should appear
• The material should be hard (what ensures
small contact area)
F
L
Composite materials:
guaiac wood
PTFE impregnated bronzes
bearing metals with graphite or MoS2
inclusions
ceramic/carbon fiber composites
Izotropic materils:
diamond
International Student Summer School „Nanotechnologies in materials engineering”
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suszko@tu.koszalin.pl
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Self-lubricating FILMS
http://www.balticnet-plasmatec.org
Hard coating
Enviromental
gas
Lubricating film
RTDinfo - Mag. Europ. Res., 39, 2003
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http://www.balticnet-plasmatec.org
An attempt - Mo2N/Cu coatings
Mo2N as a hard coating
MoO3 as a solid lubricant
Cu additive as a mean for
hardness enhancement
International Student Summer School „Nanotechnologies in materials engineering”
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suszko@tu.koszalin.pl
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http://www.balticnet-plasmatec.org
Mo2N/Cu nanocrystalline films –
structure, mechanical
and tribological properties
Outline
1.
2.
3.
4.
5.
Deposition method
Some remarks on the structure
Hardness of the films
Friction & wear in temperature range RT-400°C
Conclusions
Suszko et al., Surf. Coat. Tech., 200, 2006, pp. 6288-6292
Suszko et al., Surf. Coat. Tech., 194, 2005, pp. 319-324
International Student Summer School „Nanotechnologies in materials engineering”
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http://www.balticnet-plasmatec.org
Deposition method:
unbalanced magnetron sputtering
optical signal
Ar, N2
external coils
Cu
Mo
pulsed power
supply
pulsed power
supply
sample
30 cm
Temperature: 200 °C
Bias: -30 V
pumps
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Structure – XRD spectra
http://www.balticnet-plasmatec.org
18
16
Co Kα radiation
← Cu (111)
← γ-Mo2N (111)
γ-Mo2N (200)→
Cu (200)→ 21% at. Cu
9% at. Cu
6% at. Cu
Intensity [a.u.]
14
12
Fe (substrate)
10
1% at. Cu
8
6
4
2
0
40
0% at. Cu
45
50
55
Diffraction angle 2ϑ [°]
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65
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The influence of copper content on
crystalite size
http://www.balticnet-plasmatec.org
Crystallite size obtained from
Scherrer’s formula
13
K
Mo2N (200) t 
 cos
12
Crystallite size [nm]
AFM image of the pure
γ–Mo2N nitride
11
10
9
8
7
6
5
0
5
10
15
20
Cu content (at. %)
25
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Structure
Crystallite size and film hardness
http://www.balticnet-plasmatec.org
40
Load-depth
sensitive method
DUH 202 (FN 20 mN)
13
30
12
Traditional method
(FN 100—1000 mN)
Mo2N (200)
H (GPa)
Crystallite size (nm)
35
11
10
25
20
Load-depth
sensitive method
Hysitron (FN 2mN)
15
9
10
8
Mo2N (111)
0
5
10
15
20
25
Cu content (% at.)
7
6
5
0
5
10
15
20
Cu content (% at.)
25
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Friction coefficient
http://www.balticnet-plasmatec.org
1.0
• Normal force:
1N
0.9
• Fixed and
scanned
temperature
• Counterpart:
alumina ball
Friction coefficient
Ball on disc
configuration
•
TiN
• Speed: 5 cm/s
0 % at. Cu
3 % at. Cu
7 % at. Cu
0.8
22 % at. Cu
0.7
0.6
0.5
0.4
0.3
0
100
200
300
400
Temperature [°C]
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Wear rate coefficient - a definition
0.5
0
-0.5
-1
-1.5
1
Friction coefficient
μm
http://www.balticnet-plasmatec.org
b) 100°C
0
100
200
300
μm
400
500
600
700
0.8
0.6
0.4
0.2
0
0
1000 2000 3000 4000 5000
Revolution number
Worn volume of the sample per work unit done
against friction force
2rA
2rA
 m3 
kF 
 n

 n
 
n
 F (s)ds  Fi si 2r  Li ni L ni  J 
V
s
i 1
i 1
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A
i 1
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Wear behavior: 20-400°C
Wear rate
( m3/J )
10 -12
400°C
10 -13
Wear rate
300°C
10 -14
for TiN
RT – 0.8·10-14
200°C –
1.5·10-14
10 -15
100°C
RT, 200°C
400°C – 3·10-15
10 -16
0
5
10
15
20
25
Copper content (at. %)
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Wear behavior – "100°C effect"
http://www.balticnet-plasmatec.org
1
0.5
0
0
RT: kF ~10-16 m3/
In
Out
200 400 600 800 1000
Raman shift [cm-1]
100°C: kF ~2·10-14 m3/J !
1
0.5
0
0
In
Out
200 400 600 800 1000
Raman shift [cm-1]
200°C: kF ~10-16 m3/J
1
0.5
0
0
In
Out
200 400 600 800 1000
Raman shift [cm-1]
Mo2N 0% Cu
International Student Summer School „Nanotechnologies in materials engineering”
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Wear behavior – the influence
of Cu addtion (100°C friction test)
http://www.balticnet-plasmatec.org
0 at. % Cu
6 at. % Cu
kF ~2·10-14 m3/J
kF ~10-16 m3/J
9 at. % Cu
1 at. % Cu
50 m
50 m
2.5 at. % Cu
22 at. % Cu
50 m
50 m
50 m
50 m
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http://www.balticnet-plasmatec.org





Conclusions
Relatively low friction coefficient against
alumina is observed in room temperature.
1-3 at. % of Cu additive increases hardness
of Mo2N coatings.
Low wear rate is registered in temperatures
bellow 250°C.
"The 100°C effect" is observed for samples
with low content of copper. This effect is
eliminated when films contain >6 at. % Cu .
Coatings gradually oxidize in temperature
over 300°C.
International Student Summer School „Nanotechnologies in materials engineering”
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