Wear resistant and low friction nanocomposite coatings Dr Tomasz Suszko

Wear resistant and low frictionnanocomposite coatings

Dr Tomasz Suszko

2International Student Summer School „Nanotechnologies in materials engineering”

Warsaw - Koszalin 2006

Tomasz Suszkosuszko@tu.koszalin.pl

http://www.balticnet-plasmatec.org

• 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

Lecture outline

http://fusedweb.pppl.gov/CPEP

Plasma - the 4th

state of matter

Fundamentals of plasma sputtering– DC sputtering (diode sputtering)

Cathode

Anode+ substrate

Pressure~10 Panoble gas(e.g. Ar)

Voltage~1.5 kV

• Electron emission

• Sputtering

• Implantation

• Defects generation

• E-m radiation

Electron energy [eV]

10 100 10000.01

Disadvantages:

• Low ion current density (low sputtering rate)

• High working gas pressure resulting in scattering (low deposition rate)

• Dielectric materials can not be sputtered

• High voltage is needed

-+ 100 V

Target

0.5 kV-

Substrate Ionis

10 100 10000.01

+Lower working gas pressure – 0.1 Pa (higher deposition rate)

+Higher ion current density (higher sputtering rate)

– Dielectric materials can not be sputtered

Fundamentals of plasma sputtering– triode sputtering

10 100 10000.01

+Lower working gas pressure – 0.1 Pa (higher deposition rate)

+Higher ion current density (higher sputtering rate)

– Dielectric materials can not be sputtered

Fundamentals of plasma sputtering – microwave assisted sputtering

Target

0.5 kV–

Substrate

Microwave antenna

Substrate

Fundamentals of plasma sputtering – RF sputtering

MatchboxThe differce in:• mobility of

electrons and ions• areas of

electrodes

results in

negative target selfbias

dielectric materials can be sputtered

ca thode

vR E B

Fundamentals of plasma sputtering – motion of the electron in electromagnetic

ve cos

veve sin

ve c o s

International Student Summer School „Nanotechnologies in materials engineering”

There is a possibility to control the substrate ion current and the energy of the ions as well

– unbalanced magnetron sputtering

Substrate

Fundamentals of plasma sputtering– magnetron sputtering

DC or pulsed power supply

10 100 10000.01

+ Low working gas pressure – 0.1 Pa

+ Very high ion current density is possible (high sputtering rate)

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)

End of part one

•Mean free path•Secondary electron emmision•Ion implantation •Sputtering•Charging effect •Thermoemission•Magnetic mirror and trap •Larmor frequency and radius•Magnetron source (gun)

From yesterday

Fundamentals of plasma sputtering – reactive sputtering

Compounds of the target and gas elements For poorly conducting

or insulator deposits pulsed power supply is very usefull

Pumping system

Inert gas (e.g. Ar)Reactive gas (N2, O2, CH4 etc.)

Optical signal(optical emission spectroscopy)

• Gas pressure• Gas flows• Discharge power• (Substrate bias –

energy of the ions)• (Substrate ion

current density)

Control unit

What I won’t speak about is...

•Plasma enhanced chemical vapour deposition

•Laser ablation•Plasma spraying•Ion implantation (clasical orplasma immersion)

•Plasma nitriding orcarburazing

Plasma maintained by:• DC or pulsed discharge

(magnetron),• Vacuum arc, RF e-m waves

Plasma maintained by:• DC or pulsed discharge

(magnetron),• Vacuum arc, RF e-m waves

Working gases:• Ar (inert gas),• N2 (for nitrides),• O2 (for oxides),• CH4, C2H2 (for carbides and

Targets made of:• Ti, Al, Mo, V, Ag, Cubut also• Fe, Ni, Coand• Si

What we use for deposition is...

Coils supply

Pulsed powersupply

Substratebias

and heating

Pulsed powersupply

Spectrometer

Pumping system

Optical signal

GasesValve unit

Magnetron sources

What we develop for process control and data acquisition is...

http://www.balticnet-plasmatec.orgF

What we interest in is...

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

Where can we look for hard compounds?

Chemical sythesis ( DLC, c-BN, AlMgB, C3N4 )

Forming proper physical microstructure

• Nitride or carbide multilayers(TiN/CrN, TiN/TiAlN i in.)

• Compositesnc-MexN/a-Si3N4 nc-MexC/a-C:H np. nc-TiN/a-Si3N4

• Composites MexN/M np. (ZrN/Cu, Cr2N/Cu, TiN/Ag)

How to obtain hard films

Shear strength and hardness depend on each other thus friction coefficients are comparable for various izotropic materials.

Hardness is not all - there is friction also!

Shear strengthHardness

large small small large

Softmaterials

Hardmaterials

Self-lubricating materials

• As a result of rubbing, a thin low-shear--strengh layer should appear

• The material should be hard (what ensures small contact area)

Composite materials:

guaiac wood

PTFE impregnated bronzes

bearing metals with graphite or MoS2

inclusions

ceramic/carbon fiber composites

Izotropic materils:

diamond

RTDinfo - Mag. Europ. Res., 39, 2003

Self-lubricating FILMS

Hard coating

Enviromentalgas

Lubricating film

Mo2N as a hard coating

MoO3 as a solid lubricant

Cu additive as a mean for hardness enhancement

An attempt - Mo2N/Cu coatings

Mo2N/Cu nanocrystalline films – structure, mechanical

and tribological properties

Suszko et al., Surf. Coat. Tech., 200, 2006, pp. 6288-6292Suszko et al., Surf. Coat. Tech., 194, 2005, pp. 319-324

Outline

1. Deposition method2. Some remarks on the structure3. Hardness of the films4. Friction & wear in temperature range RT-400°C5. Conclusions

Deposition method:unbalanced magnetron sputtering

pulsed powersupply

sample

external coils

Ar, N2

optical signal

Temperature: 200 °CBias: -30 V

Structure – XRD spectra

Fe (substrate)

0% at. Cu

1% at. Cu

6% at. Cu9% at. Cu

21% at. Cu

40 45 50 55 60 65Diffraction angle 2ϑ [°]

← γ-Mo2N (111)

γ-Mo2N (200)→

← Cu (111)

Cu (200)→

Co Kα radiation

Cu content (at. %)0 5 10 15 20 25

stalli

Mo2N (200)

Crystallite size obtained from Scherrer’s formula AFM image of the pure

γ–Mo2N nitride

The influence of copper content on crystalite size

StructureCrystallite size and film hardness

Cu content (% at.)0 5 10 15 20 25

stalli

Mo2N (111)

Mo2N (200)

0 5 10 15 20 2510

Cu content (% at.)

Load-depthsensitive method

DUH 202 (FN 20 mN)

Load-depthsensitive methodHysitron (FN 2mN)

Traditional method(FN 100—1000 mN)

0 100 200 300 4000.3

Temperature [°C]

coeffi

0 % at. Cu

3 % at. Cu

7 % at. Cu

22 % at. Cu

• Fixed and scannedtemperature

Friction coefficient

• Ball on discconfiguration

• Counterpart: alumina ball

• Speed: 5 cm/s

• Normal force:1 N

Wear rate coefficient - a definition

Worn volume of the sample per work unit done against friction force

-1.5-1

0.5b) 100°C

0 100 200 300 400 500 600 700μm

0 1000 2000 3000 4000 50000

Revolution number

Wear behavior: 20-400°C

0 5 10 15 20 25

10 -15

10 -14

10 -13

10 -12

Copper content (at. %)

Wear rate( m3/J )

10 -16

400°C

300°C

RT, 200°C

100°C

Wear rate

for TiN

RT – 0.8·10-14

200°C – 1.5·10-14

400°C – 3·10-15

Wear behavior – "100°C effect"

RT: kF ~10-16 m3/

100°C: kF ~2·10-14 m3/J !200°C: kF ~10-16 m3/J0 200 400 600 800 1000

Raman shift [cm-1]

0 200 400 600 800 10000

Raman shift [cm-1]

0 200 400 600 800 10000

Raman shift [cm-1]

Mo2N 0% Cu

6 at. % Cu

9 at. % Cu

22 at. % Cu

0 at. % Cu

1 at. % Cu

2.5 at. % Cu

Wear behavior – the influence of Cu addtion (100°C friction test)

kF ~10-16 m3/JkF ~2·10-14 m3/J

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.

Wear resistant and low friction nanocomposite coatings Dr Tomasz Suszko

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