Hard, anti-wear and (or) low friction coatings Dr Tomasz Suszko - - PowerPoint PPT Presentation

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Hard, anti-wear and (or) low friction coatings Dr Tomasz Suszko - - PowerPoint PPT Presentation

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Hard, anti-wear and (or) low friction coatings Dr Tomasz Suszko What is the object of our studies? Coatings having : thickness >50nm and <100m ceramic or metallic (not polimeric-like, liquid crystals etc.) obtained

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Hard, anti-wear and (or) low friction coatings

Dr Tomasz Suszko

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

HARD

  • what is hardness?
  • what compounds can be hard?

ANTI-WEAR

  • what is wear?

LOW FRICTION - where friction come from? COATINGS

  • how do properties of a coating differ from

bulk material

What is the object of our studies?

Coatings having :

  • thickness >50nm and <100µm
  • ceramic or metallic (not polimeric-like, liquid crystals etc.)
  • obtained mainly with PVD methods
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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

What is hardness, actually? Is it a physical quantity?

On the Mohs scale (1812) a pencil lead has a hardness of 1 a fingernail has hardness 2.5 a copper penny, about 3.5 a knife blade, 5.5 window glass, 5.5

No, it isn't in any way

  • comparative, highly nonlinear

Digression: Extended Mohs scale has additional 5 stages for hardest materials 10 - fused zirconia ZrO2 11 - fused alumina Al2O3 12 - silicon carbide SiC 13 - boron carbide B4C 14 - boron nitride BN 15 - diamond

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

HR = E - e

Rockwell's hardness It also isn't any physical quantity

„Resistance of materials to plastic deformation, usually by indentation”

What is hardness, actually?

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Stress vs strain depndence

F F ultimate strength yield strength tensile strength strain hardening necking Stress Strain steel aluminium ceramics not always sharply defined F F very low ductility!

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Vicker's hardness It looks like a physical quantity

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Brinell's hardness It looks like a physical quantity too

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Different indentation geometries

Vickers (load - newtons) Brinell (load - kilonewtons) Knoop (load - decimals

  • f newtons)

Berkovich (load - mili and micronewtons) shape of the plastically deformed zone plastically deformed elastically deformed (no real border) undisturbed

What is hardness, actually?

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

What is hardness, actually?

  • It seems like a method for obtaining

compression strength

  • In fact the material is compressed,

stretched, shared, fractured

  • Hardness is not precisely defined

superposition of given material's elasticity, strength (against compression, tension, sharing and fracture)

  • Hardness is mainly expressed in

units of stress (GPa, kG/mm2)

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Indentation hardness is not a single fundamental property but a combination of properties, and varies with the type of test. The modulus of elasticity and the depth of indentation influence

  • conversions. Therefore separate conversion tables are

necessary for different materials.

Hardness conversion

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Depth-sensing (Oliver-Pharr) method

  • f hardness measurements
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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Where can we look for hard compounds?

  • Diamond, HV 8000-10000
  • Cubic boron nitride HV 5000
  • Boron carbide HV 4000
  • Silicon carbide HV 2600
  • Silicon nitride HV 1700
  • Titanium diboride HV 3000
  • Titanium carbide HV 2800
  • Titanium nitride HV 2300
  • Tungsten carbide HV 2300
  • Aluminum oxide HV 2100
  • Molibdenum nitride HV 2000
  • Chromium nitride HV 1800
  • Iron tricarbide HV 1300
  • Chromium carbide HV1300
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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

What have we

  • btained?

A monocristal :-) ? Is the structure important?

Lets cover a tool with TiN

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

As an example - very common material

  • copper
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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Metals can be made into nanocrystalline materials that perform better than regular metals. How to do it? Roll copper at the temperature of liquid nitrogen. Then, heat to around 450K Result: – Structure with micrometer sized grains and nanocrystalline grains – Increased strength and hardness of metal because of the nanocrystalline grains – High ductility

As an example - very common material

  • copper

Source: J. Schiotz et al., Nature, 391 (1998) 561

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Increasing Copper Strength

  • Plastic deformation of copper introduces work-hardening

(copper gets stronger) and reduces the grain size

  • Hall-Petch relation predicts materials get stronger as grain size

decreases: σy = σ0 + KHPd-1/2 900 MPa 100 nm Nanograin Copper 2.9 GPa 10 nm Nanograin Copper 443 MPa 400 nm Copper Cold Worked Copper Material 393 MPa Yield Strength

Can we do in endlessly? It's a pity - no.

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

TiN 2600 HV50 (26 GPa) TiN/TiAlN 4800 HV50 (48GPa) TiAlN (not presented) 3000 HV30 (30GPa)

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

source: http://www.pvd-coatings.co.uk/

Digression - balI cratering

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Digression - balI cratering

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Digression - arc deposition

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Digression - arc deposition arc magnetron

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Another example CrN/CrCN film

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Hardness depends not only on elemental or phase composition but also on structure. So, we came to nanocomposities Is it something new? Damascenian steel - do you know it?

When we google „nanocomposite”...

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Binary multilayer CrN/TiAlN

hindered crack propagation

Superhard materials

Binary nc-TiN/a-Si3N4

TiN grains a-Si3N4 "films" ≈ 10 nm 1 ML hindered crack propagation 5 nm

source: Euroschool 2008, Ljubljana; EPF, Lausanne

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

  • n-MeN/a-nitride (nMeN/a-Si3N4, where: Me=Ti, W, V)
  • n-MeN/n-nitride; for example: n-TiN/n-BN
  • n-MeC/a-C or a-C:H; for example: TiC/DLC; TiC/a-C:H,

Mo2C/a-C:H

  • n-MeN/metal, for example: ZrN/Cu, CrN/Cu, Mo2N/Cu,

Mo2N/Ag

  • n-WC + n-WS2/DLC
  • n-MeC/a-SiC, for example: TiC/a-SiC/a-C:H

Examples of nanocomposite coatings for tribological aplications

How can we obtain such composite coatings?

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

The carbon-hydrogen system

Hybridizations of carbon

sp3: four identical σ-bonds, single bonds in hydrocarbons (e.g. ethane), elemental as diamond sp: two identical σ-bonds, two extra electrons (π-bonds), triple bonds in hydrocarbons (e.g. acethylene), elemental does not exist

H3C–CH3 H2C=CH2 HC≡CH

sp2: three identical σ-bonds, one extra electron (π-bonds), double bonds in hydrocarbons (e.g. ethylene), elemental as graphite

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

DLC - diamond like carbon

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Source: J. Patscheider, Surf. Coat. Technol. 146-147 (2001) 201

Composition-structure dependence in TiN/SiN nanocomposite

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Lets come back to the hardness measurements

  • how to measure hardness of a coating?

substrate deformed zone film Thin film / large load Thick film / small load film substrate deformed zone

There is no general formula!

Hcomposite = f (L, Hfilm, Hsubstrate, tfilm) low L, high tfilm ⇒ Hcomposite = Hfilm high L, low tfilm ⇒ Hcomposite = Hsubstrate

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

How to measure hardness of a coating?

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

TiC/a-C:H nanocomposite thin films from our lab

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

X-Ray Diffraction (XRD) Sources of line broadening: Instrumental broadening

  • non ideal optics
  • wavelength dispersion
  • axial divergence od the X-ray

beam Detector resolution Finite crystallite size Extended defects

  • stacking faults

Lattice strain

Digression - calculation of crystallite size Must do we have a kind of TEM?

http://www.bmsc.washington.edu/people/merritt/bc530/bragg/

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Digression - calculation of crystallite size Must do we have a kind of TEM?

Scherrer (1918) first observed that small crystallite size could give rise to line broadening. He derived a well known equation for relating the crystallite size to the broadening, which is called the Scherrer Formula. d = K λ / (β cos θ) d = crystallite size K = Scherrer somewhat arbitrary value that falls in the range 0.87-1.0 λ = the wavelength of the radiation β half width at half maximum of a reflection (in radians) located at 2θ. Now we are able to measure crystallite size without having TEM! Though there are some limits :-(

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Crystallite size measurement accuracy

Conventional diffractometer (FWHM ~ 0.10° at 20° 2θ) Accurate Size Range < 45 nm Rough Upper Limit = 90 nm Monochromatic Lab X-ray (Cu Kα FWHM ~ 0.05° at 20° 2θ) Accurate Size Range < 90nm Rough Upper Limit < 180 nm Synchrotron (λ = 0.8 A, FWHM ~ 0.01° at 20° 2θ) Accurate Size Range < 233 nm Rough Upper Limit = 470 nm

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

TiC/a-C:H nanocomposite thin films

Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Mo2N/Ag nanocomposite thin films

Gulbinski, W. et al.., Surf. Coat. Technol. (2006) in press

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

And now lets switch to friction Where does that phenomena come from?

  • the most popular is Coulomb's model
  • the most adequate is Bowden & Tabor's concept
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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

L A L F

σ µ = =

 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 strength Hardness = = =

H AH A

σ σ

F L

A

σ σ

A A

≈

large small small large

Soft materials

F L

Hard materials

A

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

F L

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(?) material: diamond

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

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

Self-lubricating FILMS

Hard coating

Enviromental gas Lubricating film

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

How do we measure friction

somewhat disgusting...

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

How do we measure friction

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Friction and wear

 Abrasive wear  Adhesive wear

 Fretting

 Fatigue  Corrosion

 Creep  Fracture  Thermal shocks

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Friction - flash temperature

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Friction - an example

  • f temperature dependence
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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

      = = = =

∑ ∑ ∑ ∫

= = =

J m 2 2 2 ) (

3 1 1 1 n i i n i i i n i i i s F

n L A n L r rA s F rA ds s F V k

π π π

Wear rate coefficient - a definition

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

  • 1.5
  • 1
  • 0.5

0.5 b) 100°C 100 200 300 400 500 600 700 μm μm 1000 2000 3000 4000 5000 0.2 0.4 0.6 0.8 1 Revolution number Friction coefficient

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Mo2N as a hard coating MoO3 as a solid lubricant Cu additive as a mean for hardness enhancement

An attempt - Mo2N/Cu coatings

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Mo2N/Cu nanocrystalline films – structure, mechanic

ical and trib ibolo logical l propertie ies

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

2.

Deposition method

3.

Some remarks on the structure

4.

Hardness of the films

5.

Friction & wear in temperature range RT-400°C

6.

Conclusions

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Deposition method: unbalanced magnetron sputtering

pulsed power supply pulsed power supply sample external coils pumps Ar, N2 Mo Cu

  • ptical signal

30 cm Temperature: 200 °C Bias: -30 V

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Structure – XRD spectra

2 4 6 8 10 12 14 16 18 Intensity [a.u.]

Fe (substrate)

0% at. Cu 1% at. Cu 6% at. Cu 9% at. Cu 21% at. Cu 40 45 50 55 60 65

Diffraction angle 2ϑ [°]

← γ-Mo2N (111)

γ-Mo2N (200)→

← Cu (111) Cu (200)→

Co Kα radiation

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Cu content (at. %)

5 10 15 20 25 5 6 7 8 9 10 11 12 13

Crystallite size [nm]

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

ϑ β λ

cos K t =

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Structure

Crystallite size and film hardness

Cu content (% at.)

5 10 15 20 25 5 6 7 8 9 10 11 12 13

Crystallite size (nm)

Mo2N (111) Mo2N (200)

5 10 15 20 25 10 15 20 25 30 35 40

Cu content (% at.) H (GPa) Load-depth sensitive method DUH 202 (FN 20 mN) Load-depth sensitive method Hysitron (FN 2mN) Traditional method (FN 100—1000 mN)

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

100 200 300 400 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Temperature [°C] Friction coefficient

0 % at. Cu 3 % at. Cu 7 % at. Cu 22 % at. Cu

  • Fixed and

scanned temperature

TiN

Friction coefficient

  • Ball on disc

configuration

  • Counterpart:

alumina ball

  • Speed: 5 cm/s
  • Normal force:

1 N

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European Summer School PPST Koszalin August 2008

Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Wear behavior: 20-400°C

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

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Wear behavior – "100°C effect"

RT: kF ~10-16 m3/

100°C: kF ~2·10-14 m3/J !

200°C: kF ~10-16 m3/J

200 400 600 800 1000 0.5 1 Raman shift [cm-1]

Out In

200 400 600 800 1000 0.5 1 Raman shift [cm-1]

Out In

200 400 600 800 1000 0.5 1 Raman shift [cm-1]

Out In

Mo2N 0% Cu

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

6 at. % Cu

50 µm

9 at. % Cu

50 µm 50 µm

22 at. % Cu 0 at. % Cu

50 µm

1 at. % Cu

50 µm 50 µm

2.5 at. % Cu

Wear behavior – the influence

  • f Cu addtion (100°C friction test)

kF ~10-16 m3/J kF ~2·10-14 m3/J

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Tomasz Suszko tomasz.suszko@tu.koszalin.pl

Conclusions

 Relatively low friction coefficient against

alumina is observed in room temperature.

 1-3 at. % of Cu additive increases hardness

  • f 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

  • ver 300°C.