lectures 16 and 17 new trends in surface engineering...

Lectures 16 and 17

New Trends in Surface Engineering and Coating

Technologies:Superhardness and

Superlubricity

Motivation for Superhard and Lubricious Coatings

• Increased durability/long life (warranty)• Conservation

– Energy– Environment– Material

• Product safety/reliability• Economic reasons/cost• Productivity

Superhardness:Recent Developments

Hardness of Materials

• Classification of materials based on their hardness:<20 GPa : Soft Materials>20 GPa : Hard Materials

(Nitrides (TiN, CrN, TiAlN) , Carbides (TiC, WC), Carbonitrides (TiCN), DLC)

>40 GPa : Super HardMaterials (Superlattice, Nanocomposite, c-BN, Diamond, DLC, a-CNx)

Hardness:Definition,

Classification

Progress in Superhard Coatings

Hardness• Hardness is the resistance of a material to plastic deformation• Dislocation movements result in plastic deformation. • As dislocation density increases, because dislocations

movements are inhibited by each other, the hardness of the material increases.

• Grain boundaries act as a barrier to moving dislocation under stresses above yield strength of materials

• Hardness of a material depends on;– the materials crystal structure (lattice geometry and bonding

energy)– microstructure of the material (point, line and surface defects)

• dislocation density• grain size• amount and strength of grain boundaries

Definition

Nanostructured, superlatticeCoatingarchitectureFor superhardness • Major improvement in coatings technology for < 10 years

• How to maximize H/E ? “elastic strain to failure”• Hardness, Toughness and Wear resistance increase• Limitation : T-induced phase transformations & diffusion• Tribological behavior / mechanisms : still open questions …

• Obstruction of dislocation glideand crack propagation

• Grain boundary sliding

Historical concept Veprek 95 Schiotz 01

Nanocomposites• nc-metal nitride / metal Musil 99• nc-metal nitride / a-nitride (silicide) Veprek 99• nc TI-B-N system Mitterer 98, Rebholz 98• nc-metal carbide / a-C Voevodin 97-99

Zhang 03 (Review)

Barnett 03

Superlattice Barnett 03, Münz 03 (Reviews)

… after annealing at 1000°C / 1h… no hardness decrease

Courtesy of C. Donnet

Hard Coatings

• Key factors that affect crystalline rigidity or resilience of solid materials and coatings

High Coordination Numbers

Covalent Bonds

Dense atomic packing

“Hardness-Bond Type” Relation

Hard materials for nanocompositecoatings in the bond triangle and changes in properties with the change in chemical bonding

Surface Engineering: Science and Technology I, The Minerals, Metals and Materials Society, 1999, pp. 207–231.H. Holleck, in: A. Kumar, Y.W. Chung, J.J. Moore, J.E. Smugeresky (Eds.)

Origin ofHardness

Grain Size – Hardness Relation• Hall – Petch Equation

(hardness – grain size relation)

H(d) = H0 + Kd-1/2

K : Material related coefficientd : Grain size of the materialH : Hardness

• Because finer grains have more grain boundaries inhibiting dislocation movements, a decrease in grain size results in an increase in material hardness

• Below a certain grain size, grain boundary sliding becomes more dominant than dislocation movement. Such a situation decreases hardness in nano-structured materials

• General assumption for this critical grain size in the literature is that Hall-Petch equation can not be applied to the materials with grains finer than approx. 10 nm.

• For such materials, common approach is to strengthen the grain boundaries.• Grain boundary sliding causes a softening in nanocomposite materials because of the

large amount of defects in grain boundaries allowing fast diffusion of atoms and vacancies under stress.

• Below a certain grain size, this relation deviates from the actual hardness of materials due to effectiveness of the grain boundary sliding process rather than dislocation movements

Origin ofHardness

Nanocomposite Coatings

• Formulations based on the uses of immiscible elements and/or phases.

• Two main categories:- Hard phase / Hard phase

• nc-MeN / nitride (e.g., a-Si3N4, a-TiB2)(a: amorphous)

– Hard phase / Soft Phase• nc-MeN / metal (e.g., Cu, Ni, Y, Ag, Co)

Nano-Composite Coatings• Miterer et al.[1] deposited nanocrystalline phases within a metal matrix, such as

TiN in Ni, ZrN in Ni, Zr–Y–N, ZrN in Cu, CrN in Cu. The hardness of these coating systems varied from 35 GPa to approximately 60 GPa.

– In these coatings, a certain chemical affinity to each other forms high strength grain boundaries.

– The dislocation and the grain boundaries increase the hardness, while the existence of a metal matrix improves toughness. However, thermal stability is still problem

• DLC, amorphous carbon nitride or other hard amorphous materials are employed as the primary phase for the amorphous matrix and nano-sized refractory nitrides, such as TiN, Si3N4, AlN, BN, etc., are used as strengthening phases.

• TiC in DLC matrix produces a nanocomposite of hardness of 32 GPa [2]• Veprek et al [3]. deposited 4–11 nm TiN crystals in amorphous Si3N4 matrix and obtained

a coating hardness of 50–70 GPa. • Zhang et al.[4] prepared TiCrCN nanocomposite coatings with hardness of 40 GPa, in

which 8–15 nm TiCrCN crystals were formed in an amorphous DLC matrix

[1] C. Miterer, et al., Surf. Coat. Technol. 120–121 (1999) 405.[2] A.A. Voevodin, J.P. O’Neill, S.V. Prasad, J.S. Zabinski, J. Vac. Sci. Technol. A 17 (1999) 986.[3] Veprek, et al., J. Vac. Sci. Technol. B 116 (1) (1998) 19.[4] S. Zhang, Y.Q. Fu, H.J. Du, Surf. Coat. Technol. 162 (2002) 42–48.[5] Also, See MRS Bulletin, March 2003 Issue

CurrentPractices

Hard phase / Hard phaseNanocomposite Coatings

– Strong bonds at grain boundaries

– All phases are hard

– One phase is amorphous

– Decreased grain sizes

Due to Veprek’ and his group (Veprek, J. Vac. Sci. Technol. B 116 (1) (1998) 19.

Coating : nc-TiN / a-Si3N4, or a- and nc-TiB2(a:Amorphous, nc:Nanocrystalline)

TiN grain size average 3-6 nm105 GPa Hardness!!!

Scientific explanation for increased hardness:Griffith theory

Nano-structured Coatings with Super-hardness

(Veprek, 1999)

These coatings, produced by a plasma-based deposition process, can potentially minimize wear-related problems in most machine elements, hence increase their reliability

Nano-composite TiN/amorphous Si3N4

Ultrananocrystalline Diamond Films

Nano-grains are heldtogether by sp2-bondedcarbon atoms (onlyone atomic layer thick) which is perhaps responsiblefor the observed superhardness

Max. Hardness is only achieved when the grain boundaries of hard nitride phase is surrounded by a few monolayers of thin soft metals.

Hard phase surroundedBy relatively thick soft phase

Soft nano-composite

Hard phase is surrounded byA very thin soft phase

Superhard nano-composite

Hard phase / Soft phaseNanocomposite Coatings

Hard phase / Soft phaseNanocomposite Coatings

J. Musil’ and his group (Musil, et al., Surface and Coatings Technology, 115(1999) 32.)

Coating parameters – Structure – Nanocomposite coating hardness(Bias voltage, Temperature, N2 pressure eg. – XRD, SEM – Microhardness)

No particular explanation for increased hardness???

23022TiN (J.L.He)160?ZrN10125Ti-Cu-N (J.L.He*)232310-15Zr-Cu-N478,19,5Al-Cu-N301,522Ti-Cu-N (J.L.He)

35170-90CrCu-N551-238Zr-Cu-N

HardnessHardness (GPa)(GPa)% Cu (at.)% Cu (at.)Average Grain SizeAverage Grain Size(nm)(nm)

CoatingCoating

*

Deformation Mechanism of Nano-Composite Coatings

Deformation

Hardness Enhancement in Superlattices

Large ∆d0

coherency strains (Cahn 1963)

"local hardnening"

Chu & Barnett, J. Appl. Phys. 77 (1995) 4403

Shinn, Hultman, Barnett,J. Mater. Res. 7 (1992) 901

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40Multilayer period [nm]

Har

dnes

s [G

Pa]

∆Gshear∆do = 0

TiN / V0.6Nb0.4 N∆Gshear= 0∆do

V0.6Nb0.4N / NbN

NbN / VN ∆Gshear= 0∆do

TiN / NbN ∆Gshear∆do

TiN / VN ∆Gshear∆do

Increased hardness for:

Large ∆Gshear (Koehler 1970)hinder dislocation movement across phase boundaries

From where comes the strengthening?!

J.W. Cahn, Acta Met. 11 (1963) 1274M.Shinn, Hultman, Barnett, J.Mater.Res (1992)

Coherency strain hardening

Different shear moduli: ∆Gshear

GTiN

GNbN

Barriers for dislocation movement

Lattice mismatch: ∆d0

J.C. Koehler, Phys. Rev, B 2 (1970) 547S.L.Lehoczky, J.Appl.Phys. 49 (1978) 5479

3.6%mismatch NbN

TiN

Deformation study by nanoindentation• Slip lines propagate through the top TiN layer• Slip arrested at the superlattice interface

10 mN:

TiN/NbNTiN/NbNS.L.S.L.J. Molina, Clegg,

Joelsson, Hultman,unpubl.

Sample made by Focused Ion Beam (FIB) preparation

It takes 3.5 more load to induce the same damage in a TiN/NbN single-crystal superlattice

200 nm

L.Hultman, Engström, Odén, Surf. Coat. Technol. 133/34 (2000) 227J.Molina, Hultman, Phil.Mag.A82 (2002) 1983

∴ Dislocation glide confined to within layers in agrement with theory for Koehler-hardening !

(110)[1-10] slip in MgO

ΛΛ = 12 nm= 12 nm

Zone axis [100]

Pile-up

0.5 0.5 µµmm

Tensile CrackTensile Crack

No slip!No slip!

35 mN nanoscratchPlane rotation

Formation of dislocation walls & sub-grains

Reduction & expansion (!) of layer periods

13

TiC/DLC Nano-Composites

Low Crit Load, NHigh Crit Load, N

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

30 40 50 6 0 7 0 8 0 9 0 10 0

Carbon Content, at. %

Crit

ical

Load

,N

0

2

4

6

8

10

Peak

Con

tact

Pres

sure

, GPa

Super-Toughness Effect

TiC

TiC/DLC

DLC

50 N load1.0 µm thick on steel

Hardness 30 GPaElastic modulus 400 GPa

Mechanical behavior adaptation:•at low load – hard and stiff•at high load – ductile (by GB sliding)

J. Appl. Phys., 82 (1997) 855

13

200 nm

High toughness was achieved for TiC/DLC and WC/DLC hard composites because of: 1) nanocrack termination and2) ductility by grain boundary sliding.

WC/DLC Nano-Composites

0

10

20

30

40

50

60

40 50 60 70 80 90 100Carbon Content, at. %

Low

Crit

ical

Loa

d, N

Super-Toughness Effect

W-DLCWC

WC/DLC

J. V.S.T. A, 17 (1999) 986

Superlubricity or Frictionless Sliding:

Recent Developments

Friction: Resistance to sliding• From the very beginning mankind

has always been fascinated by friction and was often challenged to use, reduce, or control it to make life easier/more enjoyable.

• It is more common yet less understood than many other physical phenomena.

• Since the beginning, we often relied on it (or lack of it) for safety (or mobility).

10,000 B.C.

3,000 BC

Basic concepts&

shortcomingsTribo-mechanisms

Macro mechanisms

Holmberg 01

Micro mechanisms

Transfer

Tribochemistry

Nano mechanisms

Adhesion and Friction

Ff = σ.Ar

A1 A2

Ar = A1 + A2 + . . .

To achieve low friction both σ and Ar must be small.This means extreme hardness but very low shear strength.

Friction coefficient, µ = Ff / Fn

where, Fn is the normal force

Shear strength of contact spot

Adhesion and FrictionReal Surface Contour Real Contact Areas

Elastic/plastic Deformation

Adhesive Bonding

Shear and Recovery

Major Adhesive Forces

OTHERS- Ionic- Magneticπ-bonding/attraction

Capillary

Electrostatic

van der WaalsCovalent

Metallic

Friction vs Energy/Economic Losses

• Economic Losses in U.S. due to inadequate control of friction and wear

• Worldwide, it is estimated that 1/3 to 1/2 of world’s energyproduction is used to combat friction and wear (A. Z. Szeri, Tribology: Friction, Lubrication, and Wear; Hemisphere Publishing, 1980, p.2)

• Therefore, even very small improvements in energy efficiency (friction) and durability (wear) can save billions of dollars.

Loss Cost(b$)

Material 100Wear 100Friction 70

When lost-labor, down-time, cost of replacement parts added, these figures may double.

Latest Estimate: $500BP. Cummins/ORNL

1990 2000

10-3

10-2

10-1

1980

Teflon

MoS2, DLC H2S(g)MoS2

Fric

tion

Coe

ffici

ent,

<µ>

“NFC”

ULTRALOW FRICTION

LOW FRICTION

SUPERLOW FRICTION

Classification and History of Low-friction Materials and Coatings

WD-40

Debris entrapment

Transfer film lubrication

Tribochemicalfilm

Near-FrictionlessCarbon

Courtesy of I. L. Singer

??

0.15-0.60.20.20.10.1-0.6

B2O3Re2O7MoO3TiO2 (sub-stoichiometric)ZnO

Single Oxides

0.3-0.10.35-0.20.2-0.10.47-0.20.180.3-0.20.1

CuO - Re2O7CuO - MoO3PbO - B2O3CoO-MoO3Cs2O-MoO3NiO - MoO3Cs2O-SiO2

Mixed Oxides

0.2-0.350.15-0.20.2-0.30.15-0.250.2

AgPbAuInSn

Soft Metals

0.002-0.250.01-0.20.150-0.70.07-0.50.05-0.150.02-0.20.15-0.25

MoS2WS2HBNGraphitegraphite fluorideH3BO3GaSe, GaS, SnSe

Lamellar Solids

Typical range of Friction Coefficient*

Key Examples Classification

Classification of Low-friction or self-lubricating Materials

-Multiple slipsystems

-Low meltingpoint

-Rapid recovery/recrystallization

Higher ionic potential

Large difference in Their ionic potentials

*Strongly affected by test conditions, environment and temperature

What makes them low friction

A layeredCrystal

structure

0.1-0.50.05-0.15

Electroplated Ni and Cr films consisting of PTFE, graphite, diamond, B4C etc. particles as lubricantsNano-composite or multilayer coatings consisting of MoS2, Ti, DLC, etc.

Thin-Film (<50 micrometer) Composites

0.05-0.4Metal-, polymer-, and ceramic-matrix composites consisting of graphite, WS2, MoS2, Ag, CaF2, BaF2, etc.

Bulk or Thick-Film (>50 micrometer) Composites

0.1-0.20.2-0.40.15-0.250.04-0.15

Zinc steariteWaxesSoapsPTFE

Organic Materials/ Polymers

0.02-10.003-0.50.15-0.150.05-0.30.05-0.2

DiamondDiamond-like carbon Glassy carbonHollow carbon nanotubesFullerenes Composites

Carbon-Based Solids

0.2-0.40.15-0.2

CaF2, BaF2, SrF2CaSO4, BaSO4, SrSO4

Halides and Sulfates of Alkaline Earth Metals

Classification Cont’d

High chemical inertnessLow surface and/or chemicalinteractions

PTFE

Solidlubricant

Multi-layercoatings

Same mechanism as for oxides

Non-stick

single asperity or nano-contact

engineering surfaces

microsystem domain

F=σsA F=µN

experimental tools

AFM, IFM, SFA, QCM, HRTEM

atomistic coarse-grained continuum

micromachine devices

molecular-scale energy dissipation

constitutive laws for the interface

Lennard-Jones

simulation

Atomic ScaleContacts

MolecularDebris

POD, etc.

Superlubricity (a state of frictionless or near-frictionless sliding: In what scale?

Engines,Turbines, etc.

Courtesy of M. Dugger



microsystem domainAtomic ScaleContacts

MolecularDebris

Vanishing friction: Is it really possible?(across the boundaries)

Virtual Lab. Real Lab. Practical Application

Yes Yes/Depends Perhaps / Maybe / No

MEMS devices Industrial Gears

1Å cm-m

AFM, FFM

Vanishing Friction: MD - Simulations and Single Asperity/Nano-Contact Experiments

In virtual world, everything (including vanishing friction etc.) seems to be possible.Theoretical Studies/ Predictions:Sokoloff, Hirano, Brenner, Robbins, etc.Work by Motohisa Hirano et al.:Superlubricity: A state of vanishing friction.Both theoretically and experimentally demonstrated frictionless sliding between Si(001) and a W (011) tip in ultra-high vacuum, (PRL, 78(1997)1448)).

Hirano’s movie

Superlubricity/State of frictionless sliding



microsystem domainAtomic ScaleContacts

MolecularDebris

Vanishing Friction: Nano-scales Systems

• 0D against 1D Carbon Structures

• 1D on 1D

• 1D on 2D

• 2D on 2D

D. E. Luzzi, University of Pennsylvania

Sliding Between 0-D (C60) and 1D Carbon Structures

HRTEM

IncommensurateNo edge effectNo dangling bonds

NearlyFrictionless Sliding betweenC60 and nanotube

Luzzi’s Movie:

The Case of Nested Carbon Nanotubes (1D/1D)

Rod Ruoff - Northwestern UniversityStick-slip

Smooth Sliding

11--D Carbon Sliding Against 2D Carbon Sliding Against 2--D Carbon StructuresD Carbon Structures

Commensurate Incommensurate

Tribolever

Dienwiebel et.al.,

PRL, 92(2004)126101

µ ~ 0.001STM of one layer of

graphite

2D/2D

Dry N2

Brenner’s Movie (NC State)

Others who have also modeled/simulated/predicted frictionless sliding in graphite include:•Mate, et al., “Atomic-scale friction of a tungsten tip on a graphitesurface” PRL, 59(1987)1942.•Buzio, et al., Carbon, 40, 883 (2002).•Dienwiebel, et. al., “Superlubricity of Graphite”, PRL, 92(2004)126101.

Superlow µ in Other Materials:•Socoliuc, et al., “Entering a new Regime of Ultralow Friction”, PRL, 92(2004)134301 (Si tip over NaCl crystal)•Martin et al., Singer et al., (in-situ deposited or H2S-produced MoS2)•And others . . .

Superlow µ Citing on Graphite and Others at Nano Scale

Lattice image of graphite

STM-Graphite

Superlubricity in MoS2

• Martin et. al., 1993, (PVD-MoS2)

• Singer, et al. (In-situ H2S formed monolayers of MoS2 tested in UHV)

STM Image

N-type MoS2

Near frictionless sliding in UHV

PVD MoS2•Atomically clean & smooth surfaces

µ = 0.001

Mo

Mo

S

S

The Case ofBoric Acid

Inside Wear TrackLow Magnification High Magnification

Sliding interface

Solid Lubricant

Proposed Lubrication Mechanism for Layered Solids

Platelike crystallites are oriented in the direction of sliding.Note intercrystallite slip/shear consistent with proposed mechanism

PinOn

Disk Machine



microsystem domain

F=µNconstitutive laws for the interface


MolecularDebris

Friction Vanished (When scale is right)Practical Applications

Perhaps / Maybe / No

Summary

Yes, superlow friction was indeed achieved at

atomic/nano-scale simulations/experiments

along certain sliding directions, on certain

atomically smooth crystalline materials

that are also atomically clean and

structurally intact) (no deformation, dirt,

or asperities on surface).

Is it possible to vanish friction in micro-to-macro scale systems?

Plasmas: Ions, electrons, energetic atoms, molecules, clusters, etc

High-energyIon beams

Yes, perhaps, by designing new coatings

Microwave CVD

Sun

The ultimate plasma

PECVD

Advanced plasma-based deposition technologies may be key to achieving the kinds of super-critical,non-eqlubirium chemical/physical states needed for the synthesis of new coatings with unusual

properties, such as super-low friction.

Si

Film

Synthesis of superlow friction carbon filmsAt Argonne National Laboratory

TEMSEM

AFMH-13 - 3D

PECVD

Methane – Hydrogen Plasma

Typical plasma gas composition: 25% CH4 + 75% H2

Timeline: 1989-present

Friction Experiments: Pin-on-disk Machines

LoadSapphireBall

DiskLoad: 1 - 20 NSpeed: 0.3 - 1 m/sEnvironment: Dry NitrogenBall Radius:3.175 - 5 mm

Contact geometry Operating principles

Coating

Nearly-Frictionless Carbon (NFC)

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 1000 2000 3000 4000 5000 6000

Time (s)

Coated sapphire ball against coated sapphiredisk in dry nitrogen

0.001

Erdemir, A., et al., J. Vac. Sci. Technol., A 18(2000)1987

Load: 10 NSpeed: 0.3 m/sTemperature: 23oCBall Radius:3.175 mm

Width of WearTrack

Wear Scar (0.18 mm)

Ball Side

Disk Side

1997LoadSapphireBall

DiskLoad: 10 NSpeed: 0.3 m/sEnvironment: Dry NitrogenBall Radius:3.175 mm

0

0.005

0.01

0.015

0.02

0.025

0.03

0 1000 2000 3000 4000 5000 6000

DLC-coated SapphireDLC-coated Steel

Time (s)

Depending on Surface Roughness and/or Substrate Material, these coatings can provide friction coefficients

of 0.001 – 0.006 (in inert or vacuum environments)

Soft, less rigid, and Rough steel ball/disk

Hard, smooth and more rigid sapphireBall/disk

Fric

tion

Coe

ffici

ent Steel Substrate

Sapphire Substrate

Sliding Distance vs WearWear Volume

0.00E+00 0.00E+007.62E-06

1.22E-04

8.1E-068.0E-067.8E-06

0.0E+00

2.0E-05

4.0E-05

6.0E-05

8.0E-05

1.0E-04

1.2E-04

1.4E-04

10 50 150 250 500 5000 50000

Distance [m]

Wea

r Vol

ume

[mm

^3]

Wear TrackDisk

Ball

Ball

Load: 10 NSpeed:0.5 m/sEnvironment: Dry N2Coated Steel ballAgainst Coated Steel Disk

(Results From Naval Research Lab. Washington, D.C.)

100µm

<µ>=0.00310 100 1000

0.0000.0250.0500.0750.1000.1250.150

5.0 mm track, 3.0 mm/sec

RUN-IN

cycles

AFTERBEFORE

J. Heimberg, K. J. Wahl, I. L. Singer/NRL

µ

100µm

Third Bodies?

Evolution de f et Rc en fonction de N

0

0.05

0.1

0.15

0.2

0.25

0 500 1000 1500 2000 2500 3000

Nombre de cycles, N

Coe

ffici

ent d

e fr

otte

men

t f

0

1

2

3

4

5

6

7

Rési

stan

ce é

lect

rique

de

cont

act R

c

Frictional Performance of Argonne’s NFC Coating(Test was run at Ecole Centrale de Lyon, France)

Test Conditions: 5 N Load, 1 mm/s velocity, Steel Substrate

0.003

Courtesy of M. Bellin

Not all carbon films are created equal (at least tribologically)

0.7

0.001

0.01

0.1

1

Source Gas Chemistry

H- f

r ee

DL

C

C2H

2-G

row

n D

LC

C2H

4-G

row

n D

LC

CH

4-G

row

n D

LC

75%

CH

4+2 5

% H

2G

row

n D

LC

25%

CH

4+7 5

% H

2G

row

n D

LC

Fric

tion

Coe

ffici

ent

Test Conditions: Load, 10 N; Speed, 0.5 m/s; Temperature, 22oC; Environment, Dry N2,9.5 mm-diameter M50 Balls

H/C=0H/C=1

H/C=10

H/C=4

0.003

Plasma Discharge

PECVD

Near-FrictionlessState

Plasma gas composition has a strong influence on friction

A Model for Superlubricity of Hydrogenated Carbon Films

Super-hydrogenatedDLC

H-terminatedC atoms

+

+

WW

F

Erdemir, Surface and Coatings Technology, 146-147(2001)292

HydrogenMolecule

HydrogenAtom

BondedHydrogen

Figure 7.Courtesy of L. Curtis and P. Zapol

Sliding NFC Surfaces



microsystem domain

F=µN


MolecularDebris

Friction Vanished (When test conditions are right)

Dream Reality Practicality

Yes Yes/Depends Maybe / No

SummaryYes, superlow friction was achieved on a carbonfilm in inert gas environments and under realistic/macro-scale test conditions. But, unfortunately, in practical world, we hardly use inert environmentsand the operating conditions of most everydaymachines require the use of a lubricant and they often operate at high temperatures.

Is there still any hope?

POD

0

0.05

0.1

0.15

0.2

0.25

0 100 200 300 400 500 600

Distance (m)

Limits of Carbon-film Lubricity

Fric

tion

Coe

ffici

ent

Ambient Air, 40% R.H.

Dry Air

Dry Nitrogen

SteelBall 0.01

NFCBall H2O, H3O+,OH-

NFC6_SQ11

00.020.040.060.080.1

0.120.140.16

0 2000 4000 6000 8000 10000

Number of cycles

Fric

tion

coef

ficie

nt

0

10

20

30

40

50

RH

(%)

f RH

N2 AA N2 DA N2

Test Environment vs Friction

Load

AISI 52100Steel Ball

Disk

DLC (NFC)Film

Uncoated Ball/Coated Disk N2: Dry Nitrogen; AA: Ambient Air; DA: Dry Air;

RH: Relative Humidity

Friction

RH 0.01

Load: 10N Max. Hertz Press ~ 1 GPaSpeed: 0.1 m/s

Future Directions in the Design of Superlow Friction Coatings

SmartProcesses

(hybrids, etc.)Nanostructured,

Superlattice, Gradient

Multicomponent, Multilayer

Single component

Textured, Adaptive (smart)

Nano-composite Coatings: superhard

Self-lubricating

Sculptured Coatings

1980s 1900s 2000s

Novel Coating Architectures for the 21st Century

Historical developments and new trends in tribological and solid lubricant coatings,C. Donnet and A. Erdemir, Surface and Coatings Technology,180 –181 (2004) 76–84

Superlattice and/or multi-layer coatings

Adaptative & smart coatingsExamples

Voevodin 02

Self-adjustment of YSZ/Au/MoS2/DLC vs. Temperature & Environment

• Concept of adaptative coatings = f (temperature, environment, pressure)• Smart = adaptative + reversible

TiAlN + Y, Cr : friction-induced oxide formation Savan 99WC/DLC/WS2 : cycled air / vacuum friction Voevodin 99,00CaF2/WS2 : friction-induced CaSO4 formation at high T John 98MoS2 or WS2 / ZnO or PbO : friction induced PbMO2 or ZnWO4 Walck 97

Courtesy of C. Donnet

lectures 16 and 17 new trends in surface engineering...

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