Tribo-Mechanical Evaluations of HIPed Thermal Spray Cermet

Coatings

V. StoicaV. Stoica Heriot-Watt UniversityHeriot-Watt University,, UKUK

Rehan Ahmed

Heriot Watt University, UK

T. ItsukaichiT. Itsukaichi Fujimi Inc., Japan Fujimi Inc., Japan

S. TobeS. Tobe Ashikaga Inst. of Tech., JapanAshikaga Inst. of Tech., Japan

R. Gadow, M. EscribanoR. Gadow, M. Escribano University of Stuttgart, GermanyUniversity of Stuttgart, Germany

INTRODUCTIONThe aim of this investigation was to integrate the potential benefits of two process technologies of thermal spraying and HIPing to improve coatings tribo-mechanical performance.

The specific objectives were to improve coating strength and wear resistance by :

•Improved intersplat cohesion by HIPing post-treatment.

•Transform the mechanism of coating adhesion from mechanical interlock to metallurgical bonding.

•Improve the homogeneity and crystallinity of coating microstructure.

•The aim of this investigation was to integrate the potential benefits of two process technologies of thermal spraying and HIPing to improve coatings tribo-mechanical performance.

The specific objectives were to improve coating strength and wear resistance by :

•Improve intersplat cohesion.

•Transform the mechanism of coating adhesion from mechanical interlock to metallurgical bonding.

•Improve the homogeneity and crystallinity of coating microstructure.

POWDER

MANUFACTURE

(WC-NiCrBSiFeC)

HVOF SPRAYING

HIPing POST-TREATMENT

•Coating Microstructure (SEM, XRD)

•Mechanical Strength (Modulus, Hardness, Toughness)

•Sliding Wear Resistance (Ceramic and Metallic couples)

•Residual Stress

STARTING POWDERSTARTING POWDER

• Pre-alloying of WC-NiCrBSiFeC powders.Pre-alloying of WC-NiCrBSiFeC powders.

• Two different compositions: WC-10%NiCrBSiFeC and WC-Two different compositions: WC-10%NiCrBSiFeC and WC-40%NiCrBSiFeC were produced by the agglomeration and 40%NiCrBSiFeC were produced by the agglomeration and sintering.sintering.

WC-WC-10%NiCrBSiFeC10%NiCrBSiFeC

WC-WC-40%NiCrBSiFeC40%NiCrBSiFeC

Alloy composition: Cr 7.6%, Si 3.6%, Fe 2.4%, B 1.6%, C 0.25%, Alloy composition: Cr 7.6%, Si 3.6%, Fe 2.4%, B 1.6%, C 0.25%, Ni Bal.Ni Bal.

WC-10%Ni alloy WC-10%Ni alloy (400(400m)m)

440C steel substrate (8mm thick)440C steel substrate (8mm thick)

THERMAL SPRAYINGTHERMAL SPRAYING• Functionally graded coatings were produced by the Functionally graded coatings were produced by the

HVOF (JP5000) process on 440-C bearing steel substrate HVOF (JP5000) process on 440-C bearing steel substrate to minimise the mismatch of thermal and elastic to minimise the mismatch of thermal and elastic properties. properties. • The spraying parameters were as follows:The spraying parameters were as follows:

Oxygen flow – 893 lit/minOxygen flow – 893 lit/minKerosene flow – 0.321 lit/minKerosene flow – 0.321 lit/minspraying distance – 380 mmspraying distance – 380 mmSpraying rate – 50 g/minSpraying rate – 50 g/min

Shot-blasting WC-40%Ni alloy WC-40%Ni alloy (100(100m)m)

Grinding and polishing

32 mm diameter

• Two Different HIPing temperatures of 850oC and 1200oC were adapted at a pressure of 150 MPa.

• Cooling and heating rates were optimised to 4oC/minute.

• Holding time was 60 minutes.

• Uncapsulated HIPing conditions.

HIPing POST-TREATMENTHIPing POST-TREATMENT

COATING COATING MICROSTRUCTURE MICROSTRUCTURE

Substrate

WC-40NiCrBSi

WC-10NiCrBSi

As sprayed coatingsAs sprayed coatings

SubstrateWC-40NiCrBSi

WC-10NiCrBSi

HIPed at 850HIPed at 850ooC coatingsC coatings

Substrate

HIPed at 1200HIPed at 1200ooC coatingsC coatings

7µm 7µm7µm

10µm 10µm10µm

-WC

-WC

-WC

-WC

-WC -W

C

-WC

-Ni 3B

-W2C

-Ni

-W2C

-Fe

W3C

-W

As-sprayed coating -W2C

XRD EVALUATIONSXRD EVALUATIONSPowder vs. Sprayed CoatingPowder vs. Sprayed Coating

10 20 30 40 50 60 70 80 90

-WC

-WC

-WC

-WC -W

C

-WC

-NiB

-Ni

-Ni

Starting powder

WC

WC

-WC

-WC

-WC

-WC

-WC

HIPed at 1200oC

-WC

-WC

-Ni

-Ni 2S

i

-Ni 2W

4C

-Ni 3B

-Ni 5S

i 2

-Fe

W3C

-Ni 2W

4C-N

i 4B3

-Ni 4B

3

-Fe

W3C

WC-W

C

-Ni

-WC

-WC

-WC

-WC -W

C

-WC

-Ni 3B

-W2C

-W2C

-FeW

3C

10 20 30 40 50 60 70 80 90

W

-W2C

As-sprayed coating-W

C

-WC

-WC

-WC

-WC -W

C

-Ni

-Ni 2W

4C -Fe

W3C

-W2CHIPed at 850oC

XRD EVALUATIONSXRD EVALUATIONSSprayed and HIPed coatingsSprayed and HIPed coatings

MIROHARDNESS MIROHARDNESS EVALUATIONSEVALUATIONS

Substrate

WC-40%NiCrBSi

WC-10%NiCrBSi

0

200

400

600

800

1000

1200

1400

0 50 150 250 350 450

As-sprayed

HIPed at 850

HIPed at 1200

Vic

kers

Har

dnes

s

Distance from Surface (µm)

INDENTATION MODULUS INDENTATION MODULUS =E(1-=E(1-22))

As-Sprayed

HIPed at 850oC

HIPed at 1200oC

0

50

100

150

200

250

300

350

400

450

0 50 100 150 200 250 300 350 400

Distance from Surface (µm)

Inde

ntat

ion

Mod

ulus

(G

Pa)

WC-40%NiCrBSiWC-10%NiCrBSi

Surface

As sprayed coatingsAs sprayed coatings HIPed at 850C coatingsHIPed at 850C coatings HIPed at 1200C coatingsHIPed at 1200C coatings

SEM observations: HVOF coatingsSEM observations: HVOF coatings

Cryogenic fractured coatingsCryogenic fractured coatings

micro-crackspores

pores

As-sprayed coatingAs-sprayed coating

INDENTATION TOUGHNESS INDENTATION TOUGHNESS

200 m

HIPed at 850HIPed at 850ooC coatingC coating

200 m

HIPed at 1200HIPed at 1200ooC coatingC coating

200 m

Cracks

Sliding directionSliding direction

SLIDING WEAR SLIDING WEAR TESTS TESTS

Reciprocating ball on plate apparatusReciprocating ball on plate apparatus

Normal Normal loadload

Ball

Coating

Test conditionsTest conditions

Counter Body(balls)

440C Steel

SiSi33NN44 ceramic ceramic

Load 12 and 22 N

Sliding Speed

0.012m/s

Dry/Lubricated

Dry

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

HIPed at 1200oC

Vol

ume

loss

(m

m3)

As-sprayed HIPed at 850oC

Coatings Vs steel, 12N loadCoatings Vs steel, 22N load

Coatings Vs ceramic, 12N loadCoatings Vs ceramic, 22N load

SLIDING WEAR: SLIDING WEAR:

COATING VOLUME COATING VOLUME LOSSLOSS

SLIDING WEAR: WEAR SLIDING WEAR: WEAR SCARSSCARS

As-sprayed coatingAs-sprayed coating

HIPed at 850HIPed at 850oC coatingC coating HIPed at 1200HIPed at 1200oC coatingC coating

Three dimensional interferometric plots of the coatings Three dimensional interferometric plots of the coatings tested against ceramic balls (load – 22N)tested against ceramic balls (load – 22N)

0

0.2

0.4

0.6

0.8

1

Total volume loss, 12N load

Total volume loss, 22N load

As-sprayed HIPed at 850oC HIPed at 1200oC

Total volume loss (mm3)

SLIDING WEAR: TOTAL VOLUME SLIDING WEAR: TOTAL VOLUME LOSSLOSS

Total volume loss – Total volume loss – Coatings Vs steel ballsCoatings Vs steel balls

SLIDING WEAR: TOTAL VOLUME SLIDING WEAR: TOTAL VOLUME LOSSLOSSTotal volume loss – Total volume loss – Coatings Vs ceramic ballsCoatings Vs ceramic balls

0

0.02

0.04

0.06

0.08

0.1

As-sprayed HIPed at 850oC HIPed at 1200oC

Ball volume loss, 12N loadCoating volume loss, 12N load

Ball volume loss, 22N loadCoating volume loss, 22N load

To

tal v

olu

me

loss

(m

m3)

Why improvement in wear resistance?

FRICTION FRICTION

0

0.2

0.4

0.6

0.8

1

1.2

1.4

100 200 300 400 500 600

As-sprayed

HIPed at 850oC

HIPed at 1200oC

Friction coefficient

Time (mins)

Coatings Vs steel balls (load - 22N)Coatings Vs steel balls (load - 22N)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

100 200 300 400 500 600

Time (mins)

Coatings Vs ceramic balls (load - 22N)Coatings Vs ceramic balls (load - 22N)

As-sprayed

HIPed at 850oC

HIPed at 1200oC

Friction coefficient

SLIDING WEAR: WEAR SLIDING WEAR: WEAR MECHANISMSMECHANISMS

As-sprayed coatingsAs-sprayed coatings HIPed at 850HIPed at 850oC coatingC coatingHIPed at 1200HIPed at 1200oC coatingC coating

SEM micrographs within the wear tracks of the SEM micrographs within the wear tracks of the coatings tested against steel (load – 12N)coatings tested against steel (load – 12N)

RESIDUAL STRESS RESIDUAL STRESS MEASUREMENT MEASUREMENT

-1400

-1200

-1000

-800

-600

-400

-200

0

0 20 40 60 80 100 120 140 160 180 200 220

Res

idua

l str

ess

(MP

a)

Distance from the surface (µm)

As-sprayed

HIPed at 850C

HIPed at 1200C

CONCLUSIONSCONCLUSIONS1.1. Uncapsulated HIPing can be successfully applied to Uncapsulated HIPing can be successfully applied to

post-treat thermally sprayed coatings. post-treat thermally sprayed coatings.

2.2. HIPing post-treatment can improve the sliding wear HIPing post-treatment can improve the sliding wear resistance of thermal spray cermet coatings.resistance of thermal spray cermet coatings.

3.3. Wear resistance improves with the increase in HIPing Wear resistance improves with the increase in HIPing temperature. temperature.

4.4. Improvement in sliding wear resistance is thought to Improvement in sliding wear resistance is thought to originate from the increase in coating’s hardness, originate from the increase in coating’s hardness, elastic modulus and fracture toughness.elastic modulus and fracture toughness.

5.5. HIPed coatings show WC recovery and formation of HIPed coatings show WC recovery and formation of complex carbides.complex carbides.

6.6. Results indicate higher elastic modulus after HIPing Results indicate higher elastic modulus after HIPing due to higher bonding between lamellas.due to higher bonding between lamellas.

WORK IN PROGRESSWORK IN PROGRESS

Influence of HIPing pressure, HIPing vs. Vacuum Heat Treatment.

Influence of Coating Materials, especially WC-Co Coating Substrate Bonding Mechanism. Measurement of Adhesive and Cohesive strength. Optimisation of HIPing Parameters Influence on Fatigue and Impact performance