Georgia Institute of Technology, Technion - IIT

Mechano-Chemical

Surface Modification With Cu2S:

Inducing Superior Lubricity

Michael Varenberg, Grigory Ryk, Alexander Yakhnis,

Yuri Kligerman, Neha Kondekar, Matthew T. McDowell

Tribology Labs @ Mechanical Engineering

2Lubricated Friction

Friction C

oeffic

ient

Viscosity Velocity

Load

Full-film

h >> Rh ≈ R

h → 0

Boundary

Mixed

Solid 1

Solid 2

Lubricant

FN

vh

Surface roughness, R

3Friction in Boundary Lubrication

I – Nonpolar base oil

II – Fatty acid dissolved in the base oil: reacts with the metallic surface

forming a metallic soap

III – EP additive dissolved in the base oil: reacts when Tr is reached

IV – Hypothetical curve for an effective combination of II and III

Temperature

Tm(II)

0.1

0.2

0.3

Friction c

oeffic

ient

Tr(III)

0.4

0.5

IV

Tm(III)High Low

4Surface Film Formation

Approach State-of-the-art

InputExtreme pressure and anti-wear agents

containing S, Cl, P, etc.

Methods

and

means

Complex formulation

of general-purpose oil

as a mean of transportation

Uncontrolled interaction

during service

Outcome Non-uniform surface film

ImpactGood oil lubricity leading

to low friction and wear

Approach State-of-the-art Hypothesized

InputExtreme pressure and anti-wear agents

containing S, Cl, P, etc.

Methods

and

means

Complex formulation

of general-purpose oil

as a means of transportation

Simple

direct

tailored

surface treatment

during

manufactureUncontrolled interaction

during service

Outcome Non-uniform surface film Uniform surface film

ImpactGood oil lubricity leading

to low friction and wear

Superior oil lubricity leading

to ultra-low friction and wear

5Surface Finishing Processes

Abrasive processesGrinding, honing, lapping,

polishing, etc.

Cold-working processesShot peening, laser-shock peening,

burnishing, etc.

6Deformation Induced Diffusion

The surfaces are activated by heat and rupture of atomic

bonds at newly generated grain boundaries and dislocations.

This leads to anomalous acceleration of the diffusion activity.

Given the presence of such elements as sulfur, chlorine or

phosphorus in the immediate environment DURING the

finishing mechanical treatment, stable lubrication-beneficial

subsurface layers can be formed in advance

7

FeSFe S? ?

Al2O3

Fe

Al2O3

Fe

Potential Pathway

Cu2S

FeS

Cu2S

Cu

Cu2SCu

FeS

Cu CuDisplacement reaction

Al (-1.662)

Fe (-0.447)

Mo (-0.200)

W (0.100)

Cu (0.342)

Most reactive

Least reactive

8Surface Treatment

Particles

Shield

Specimen

Carrier gas

Vibrating

reservoir

Peened surface Nozzle

Treated surfaces: Ground cast iron

Shot peening media: Al2O3, size 44-75 mm, and Cu2S, size <44 mm

Carrier gas: N2, pressure 2 bar

9Material and Surface Properties

Material Al2O3 Cu2SCast

iron (CI)

CI after

Al2O3

CI after

Cu2S

CI after

Al2O3+

Cu2S

Mild

steel

UseShot peening

media

Tested

surfaces

Counter

surface

Hardness,

HV2,600 90 191±16 250±35 214±52 256±25 307±39

Ra, mm - - 2.3 1.0 0.7 1.0 0.3

10Experimental Details

0

150

100

50

Time, s0 150 300 450 600 750 900 1050

Speed, rpm

5

8

7

6

Friction force, N

F

L

Load

Friction gage

Ring sample Spindle axis

Block sample

Moving

block

holder

Rings: Mild steel

Blocks: Grey cast iron

Loads: 30, 50 N Speeds: 0.1-0.9 m/s

Lubrication: SN90 base oil, 55 cPa s @ 30 °C, 2 drops/min

11Frictional Performance

Al2O3+Cu2S

Cu2S

Al2O3

Reference

Speed/load, m s-1 N-1

0.001 0.010

0.06

0.04

0.02

Frictio

n c

oe

ffic

ien

t

0.10

0.16

0.14

0.12

0.08

30 N

50 N

12X-ray Photoelectron Spectra

0

2

4

6

8

10

12×103

Inte

nsity,

counts

85 80 75 70 65

Binding energy, eV

Reference

Al2O3

Cu2S

Al2O3+Cu2S

Cu 3p1/2

Cu 3p3/2 Al 2p

0

5

10

15

20

25

30×103

Inte

nsity,

counts

960 950 940 930

Binding energy, eV

Reference

Al2O3

Cu2S

Al2O3+Cu2S

Cu 2p1/2

Cu 2p3/2

0

1

2

3

4

5

7×103

Inte

nsity,

counts

175 170 165 160

Binding energy, eV

Reference

Al2O3

Cu2S

Al2O3+Cu2S

S 2p

6

13Worn Surfaces

40 mm

Not peened Peened with Al2O3

Peened with Cu2S Peened with a blend of

Al2O3 and Cu2S

40 mm

40 mm 40 mm

14Summary

• A direct route to the formation of a surface layer of

superior lubricity is presented as an alternative to the

use of oil additives for friction reduction

• An ultra-low friction coefficient of about 0.01 is obtained

with base oil lubrication after shot peening the surface

using a mixture of Cu2S and Al2O3

• Preliminary results suggest that the surface treated with

a blend of Al2O3 and Cu2S particles exhibits high wear

resistance

Varenberg, Ryk, Yakhnis, Kligerman, Kondekar and McDowell, Tribol. Lett. 64 (2016) 28

15Acknowledgments

Yuri

Kligerman

Grigory

Ryk

Alexander

Yakhnis

Neha

Kondekar

Matthew T.

McDowell

Carl E. Schustak Energy Research and Development Fund

New York Metropolitan Research Fund