superhard coatings for advanced vehicle systems applications

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SUPERHARD COATINGS FOR ADVANCED

VEHICLE SYSTEMS APPLICATIONS

Ali Erdemir and Dileep Singh

Tribology Section

Energy Technology Division

April 19, 2006



Rationale and Goals

Injectors

Design and develop new

coatings to reducefriction

Demonstrate their

energy saving and wear

reducing benefits

Scale-up and transfer

optimized technology to

industry

Powertrain components

Piston pins

• Nearly 10% of fuel energy

is consumed by friction in

engines (which amounts to

about one million barrels

of oil/day)

Gears



Approach

Design superhard coating composition for intended

applications

Develop a reliable deposition protocol for the

production of superhard coatings

Characterize structure and property

Demonstrate performance

Analyze test data and examine sliding surfaces

Determine friction and wear mechanisms

Integrate superhard coatings with laser texturing

Prepare reports



Industrial Collaborations

Burgess-Norton performing tests in fired engines

(interested in licensing the technology)

Eaton (a CRADA is underway)

Caterpillar

BorgWarner

Westport

Federal Mogul

Coating Systems Manufacturers (HauzerTechnoCoating, Ion Bond, CemeCon).



Technical Accomplishments

Successfully produced superhard coatings in a production-

scale sputter ion plating system

Demonstrated their superhard and low-friction nature

Verified their extreme resistance to scuffing and wear

Demonstrated their compatibility with and superior

performance in EGR-contaminated oils Initiated surface analytical studies to understand lubrication

mechanisms

First measurements of residual stresses in thin coatingsmade using X-rays at the Advanced Photon Source

Collaborated with an outside company to demonstrate its

performance in piston pin applications



Upper Surface

Lower Surface

Lubricant

BoundaryLayersAsperity Contacts

Mechanical

Seals

Boundary Lubrication

Mixed

LubricationFull Film

Lubrication

Viscosity * Speed/Load

F r i c t i o n

C o e f f i c i e n t

? ?

Schematic Illustration of Boundary Lubrication

Big Question ?:

Can we design coating systems thatare not only superhard (for wear

control) but also low-friction (forfriction control) under severe boundarylubricated sliding conditions?

In these components friction

and wear result mainly from

direct metal-to-metal contacts

which often occur under highpressures, low sliding

velocity and in low viscosityoils.

Major Causes of Friction in Lubricated Contacts



Conventional Hard Coatings

Design and Synthesis of a Superhard,Nanocomposite Coating

Superhard nano-composite

coating

0

0.02

0.04

0.06

0.08

0.1

0.12

0 5 10 15

KTF 210

Depth

Load (mN)

E/(1-v2) = 401.23 +/- 17.18 (GPa)

Hardness = 67015 +/- 4683 (N/mm2)

Wp = 0.14 nJ (%15)

We = 0.79 nJ (%85)

Substrate

Cross-Section electron

Microscopy image of

New, nano-structured

Coating

Nano

Grains

Optimization of depositionprocess parameters is keyto the development of these

novel coatings providingsuperhardness, toughnessand exceptional friction andwear properties.

Superhard:

67GPa

Patent Pending

Two more invention disclosures filed

High-mag image

Sputter ion plating system

Hardness Behavior

SEM Cross-section Images



0

0.05

0.1

0.15

0.2

0 2 104

4 104

6 104

8 104

1 105

Time (s)

Friction and Wear Performance UnderBoundary Lubrication Regime

Wear track

No noticeable wear

1.6X

Steel Pin/Steel Disk

Steel Pin/Superhard coated steel

Load: 20N, Velocity: 10 rpm,

10W30 Formulated Synthetic Oil

Boundary Lubrication

Mixed

LubricationFull Film

Lubrication

Viscosity * Speed/Load

F r i c t i o n

C o e

f f i c i e n t

No measurable wear

F

r i c t i o n

C o e f f

i c i e n t

More than 75% reduction in friction



0

200

400

600

800

1000

0 500 1000 1500 2000 2500

Time (Sec)

Normal Load

Steel / Steel

SHC / Steel

SHC / SHC

SHC - Super Hard Coating

Effect of SHC on scuffing resistance of steel surfaces

Test Configuration : Block on Ring ConfigurationLubricant - PAO 10 basestock

Speed - 750 rpmTemperature - Ambient RT

L o a d

( N )

BlockOn

Ring

Could not be scuffed.

Test was terminateddue to overheating

of oil that produced

heavy smoke.

Resistance of Superhard Coatings to Scuffing

Base oil



0.00

0.05

0.10

0.15

0.20

0 480 960 1440 1920 2400 2880 3360 3840 4320

Time (s.)

F r i c t i o n C o

e f f i c i e n t

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Friction CoefficientRing Temp.Load

L o

a d ( N )

R i n g T e m p * 1 0 - 3

Mobil 1 10W30

Resistance of Superhard Coatings to Scuffing Cont’d



Surface Analytical Studies

(Preliminary TOF-SIMS Results)

SHC coated ring vs.

SHC coated blockIn Mobil 1 10W-30

Total Ion PO2

FeS SBlue FeS

Red S



Tests were run at high

speed (hence high

temperature) for

100 hours in a V8engine.

Field Test Results:Superhard Coatings on Piston Pins

Control pin

Superhard-coated

pin

We had four coated pins in one bank of a V8 engine.

The other 4 cylinders only had manganese phosphate

coated pins (control pins).



Summary

A family of superhard coatings was successfully

developed

Their superior friction, wear, and scuffing

performance was demonstrated

Their resistance to EGR-contaminated diesel

engine oils was confirmed

Fundamental surface analytical studies and x-ray

stress measurements were initiated

Excellent results were obtained from limited field

tests and more work is underway



Future Plans

Perform bench-top life and field tests

Determine the effects of oil viscosity on friction and wear

Perform more tests in EGR contaminated oils; explorecorrosion/erosion related degradation

Elucidate lubrication mechanism(s) using surfacesensitive techniques (UIUC, ANL-APS).

Elucidate the extent of internal stresses and correlatefindings with performance and durability.

Integrate superhard coatings with laser surface texturing

to further enhance performance/durability Increase collaboration with industry, establish programs,

transfer technology (potential customers; Caterpillar,

Eaton, Federal Mogul, Burgess-Norton, Ford).



Rationale: Residual Stress Measurements inThin Coatings

Reduction of friction and wear in drive trains and

engine components, and consequently, reduction in

parasitic energy losses can result in >6% fuel savings

Performance of low friction and wear coatings is

strongly dependent on the residual stress profiles

Currently, no technique is available to profile residual

stresses in thin coatings

This is a new program in FY 06



Objectives

Develop and refine high-energy X-ray technique(s) at the

Advanced Photon Source (APS) to measure residual

strains/stresses for super-hard, nanocrystalline low-friction

coatings as a function of coating thicknesses

Correlate residual stresses in coatings systems to processing

technique and variables, material properties, and adhesionenergies

Compare experimentally measured residual stresses to calculated

stresses from finite element modeling

Develop an optimized coating processing protocol for a specific

coating system and applications

Diff ti l A t X R Mi



Differential Aperture X-Ray Microscopy(DAXM)

Residual strains measured by comparing

shift in diffraction spot positions from grains

at specific coating depth with those of

unconstrained grains

X-ray absorbing wire allows depth profiling

Depth resolution of ~0.5 µm is achievable

CCD

X-ray beam

Wire

Substrate

Film



Cross-Section Depth Resolved X-RayMicroscopy (CDRXM)

Samples fractured to expose cross-section

Depth of X-ray penetration dependent on

energy (~ 5-10 µm)

Sample moved in steps of 0.25 µm to scan

surface of the film to substrate

Invention report filed

CCD

X-ray beam

FilmSubstrate



Coating Systems Investigated

SHC on Si SubstrateMo on Si Substrate

Samples fabricated by O. Eryilmaz (ANL)

Sputter deposition

200-300°C deposition temperature

Ar pressure and sputtering bias

Coating thicknesses ~ 3-5 µm

Residual strains measured on as-fabricated and annealed (500

C for 1 h) samples



Diffraction Data from CDRXM

R id l t i d b



Residual strains measured byCDRXM: Mo coating

x

z

y

Si

Mo

Mo-large

grains

bond coat

SiCTE = 2.6 ppm/K

MoCTE = 4.8 ppm/KX-Rays

Residual strains measured by CDRXM:



Residual strains measured by CDRXM:SHC on Si substrate

x

z

y

Si

SHC

Mo-large

grains

bond coat

SiCTE = 2.6 ppm/K

SHCCTE = ? X-Rays



Summary

For the first time, depth resolved residual strains in thin coating

systems has been measured using CDRXM technique

CDRXM technique, with sub-micron resolution, allows strainmeasurements even in the bond coat

In-plane strains for Mo and SHC coatings are tensile and for the

Mo bond coat they are compressive Magnitude of in-plane strains in SHC coating is significantly higher

than in Mo coating and decrease from surface to the interface

Annealing significantly decreases the in-plane strains for SHC,however, for Mo films, decrease in in-plane strains is relatively

smaller



Future Plans

Compare residual strain measurements obtained from DAXM and

CDRXM techniques (FY 06)

Characterize coating adhesion properties using mechanical testssuch as nano-indentation (FY 07)

Compare strain measurements with FEM (FY 07)

Measure residual strains/stresses in thin coatings fabricated undervarious processing conditions (FY 07)

Correlate coating performance & adhesion with residual stresses

& processing (FY 08) Develop a protocol for developing coatings with optimal properties

(FY 08)

Establish industrial collaborations to transfer the technology



Contributors

O. Eryilmaz

G. Chen

B. Larson (ORNL)

J. L. Routbort

Weijin Liu

superhard coatings for advanced vehicle systems applications

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