SUPERHARD COATINGS FOR ADVANCED VEHICLE SYSTEMS APPLICATIONS

Ali Erdemir and Dileep SinghTribology Section

Energy Technology Division

April 19, 2006

Rationale and Goals

Injectors

Design and develop new coatings to reduce friction

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 performanceAnalyze test data and examine sliding surfacesDetermine friction and wear mechanismsIntegrate superhard coatings with laser texturingPrepare reports

Industrial Collaborations

Burgess-Norton performing tests in fired engines (interested in licensing the technology)Eaton (a CRADA is underway)CaterpillarBorgWarnerWestportFederal MogulCoating Systems Manufacturers (Hauzer TechnoCoating, Ion Bond, CemeCon).

Technical Accomplishments

Successfully produced superhard coatings in a production-scale sputter ion plating systemDemonstrated their superhard and low-friction natureVerified their extreme resistance to scuffing and wearDemonstrated their compatibility with and superior performance in EGR-contaminated oilsInitiated surface analytical studies to understand lubrication mechanismsFirst measurements of residual stresses in thin coatings made using X-rays at the Advanced Photon SourceCollaborated with an outside company to demonstrate its performance in piston pin applications

Upper Surface

Lower Surface

LubricantBoundaryLayersAsperity Contacts

Mechanical Seals

Boundary Lubrication

MixedLubrication Full Film

Lubrication

Viscosity * Speed/Load

Fric

tion

Coe

ffici

ent

? ?

Schematic Illustration of Boundary Lubrication

Big Question ?: Can we design coating systems that

are not only superhard (for wear control) but also low-friction (for friction control) under severe boundary lubricated sliding conditions?

In these components friction and wear result mainly from direct metal-to-metal contacts which often occur under high pressures, low sliding velocity and in low viscosity oils.

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 electronMicroscopy image of New, nano-structured Coating

NanoGrains

Optimization of deposition process parameters is key to the development of these novel coatings providing superhardness, toughness and exceptional friction and wear properties.

Superhard:

67GPa

Patent PendingTwo 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 Under Boundary 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

MixedLubrication Full Film

Lubrication

Viscosity * Speed/LoadFr

ictio

n C

oeffi

cien

t

No measurable wear

Fric

tion

Coe

ffici

ent

More than 75% reduction in friction

0

200

400

600

800

1000

0 500 1000 1500 2000 2500Time (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 basestockSpeed - 750 rpmTemperature - Ambient RT

Load

(N)

BlockOn

Ring

Could not be scuffed.Test was terminated due to overheatingof oil that producedheavy 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 4320Time (s.)

Fric

tion

Coe

ffici

ent

0

200

400

600

800

1000

1200

1400

1600

1800

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Friction CoefficientRing Temp.Load

Load

(N)

Rin

g Te

mp

*10-3

Mobil 1 10W30

Resistance of Superhard Coatings to Scuffing Cont’d

Surface Analytical Studies(Preliminary TOF-SIMS Results)

SHC coated ring vs. SHC coated block In 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 V8 engine.

Field Test Results: Superhard Coatings on Piston Pins

Control pin

Superhard-coatedpin

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 developedTheir superior friction, wear, and scuffing performance was demonstratedTheir resistance to EGR-contaminated diesel engine oils was confirmedFundamental surface analytical studies and x-ray stress measurements were initiatedExcellent results were obtained from limited field tests and more work is underway

Future PlansPerform bench-top life and field testsDetermine the effects of oil viscosity on friction and wear Perform more tests in EGR contaminated oils; explore corrosion/erosion related degradationElucidate lubrication mechanism(s) using surface sensitive techniques (UIUC, ANL-APS).Elucidate the extent of internal stresses and correlate findings 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 in Thin 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 adhesion energies

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

Differential Aperture X-Ray Microscopy (DAXM)

Residual strains measured by comparing shift in diffraction spot positions from grains at specific coating depth with those ofunconstrained 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-Ray Microscopy (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 Substrate Mo on Si Substrate

Samples fabricated by O. Eryilmaz (ANL)

Sputter deposition200-300°C deposition temperatureAr pressure and sputtering biasCoating thicknesses ~ 3-5 µm

Residual strains measured on as-fabricated and annealed (500°C for 1 h) samples

Diffraction Data from CDRXM

Residual strains measured by CDRXM: Mo coating

x

z

y

Si

Mo

Mo-large grains bond coat

SiCTE = 2.6 ppm/KMoCTE = 4.8 ppm/K

X-Rays

Residual strains measured by CDRXM: SHC on Si substrate

x

z

y

Si

SHC

Mo-large grains bond coat

SiCTE = 2.6 ppm/KSHCCTE = ? X-Rays

SummaryFor the first time, depth resolved residual strains in thin coating systems has been measured using CDRXM technique CDRXM technique, with sub-micron resolution, allows strain measurements 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 PlansCompare residual strain measurements obtained from DAXM and CDRXM techniques (FY 06)Characterize coating adhesion properties using mechanical tests such as nano-indentation (FY 07)

Compare strain measurements with FEM (FY 07)

Measure residual strains/stresses in thin coatings fabricated under various 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

ContributorsO. EryilmazG. Chen

B. Larson (ORNL)

J. L. Routbort

Weijin Liu