Influence of Post-treatment on the Tribo-mechanical properties of - - PDF document

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Influence of Post-treatment on the Tribo-mechanical properties of Cermet Coatings R. Ahmed, S. Stewart, V. Stoica Heriot-Watt University, UK Y. Itsukaichi Fujimi Inc., Japan HIPing Post-treatment Previous Investigations 1) Kuribayashi,

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Influence of Post-treatment on the Tribo-mechanical properties of Cermet Coatings

  • R. Ahmed, S. Stewart, V. Stoica

Heriot-Watt University, UK

  • Y. Itsukaichi

Fujimi Inc., Japan

HIPing Post-treatment – Previous Investigations

1) Kuribayashi, H., Suganuma, K., Miyamoto, Y., & Koizumi, M., “Effect of HIP treatment on plasma sprayed coating onto stainless steel”, American ceramic society bulletin, 65(9), 1306-1310, (1986). Al2O3, ZrO2 and TiC plasma spray coatings HIPed (Capsulated) at 1100 to 1300oC for 1hour at 100MPa - Remarkable improvements in hardness and tensile strength. 2)

  • H. Ito, Nakamura, R., Shiroyoma, M., & Sasaki, T., “Post-treatment of

plasma sprayed WC-Co coatings by hot isostatic pressing”, NTSC, CA, 233- 238, (1990). WC-Co plasma spray coatings HIPed (Capsulated) at 500 to 1000 oC for 30 minutes at about 5MPa – Remarkable improvements in hardness and abrasive wear resistance. Lamellar to granular transformation. 3) Khor, K.A. & Loh, N. L., “Hot isostatic pressing of plasma sprayed Ni-base alloys”, JTST, 3(1), 57-62, (1994). Numerous studies on Capsulated and uncapsulated HIPing of plasma sprayed NiCrAl and ZrO2-Y2O3 coatings – Improvement in hardness and modulus, reduction in porosity.

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Project Background

  • S. Tobe, Y. Ando, R. Ahmed and V. Stoica, “Enhancement of wear and mechanical

properties of thermally sprayed WC-Co coatings by HIPing post-treatment”, Tribology in Environmental Design, Second International conference, Bournemouth, UK, ISBN 1 860584152, 119-127, 2003.

As- Spray ed (Not HIPe d) Yes Yes Yes No Yes Capsulation 60 120 60 60 60 Holding Time (minutes) 150 150 150 150 150 Pressure (MPa) 1000 900 900 850 850 Temperature (oC) AS HC-5 HC-4 HC-3 HC-2 HC-1 HIP Code

Project Background (WC-Co coatings)

a) As sprayed sample (AS) b) HC-1 sample c) HC-2 sample d) HC-3 sample e) HC-4 sample f) HC-5 sample

HIPed @800oC (Capsulated) HIPed @800oC (Not Capsulated) HIPed @900oC (Capsulated) HIPed @900oC (Capsulated) HIPed @1000oC (Capsulated) As-Sprayed Coating Holding Time = 1 hour Holding Time = 1 hour Holding Time = 1 hour Holding Time = 1 hour Holding Time = 2 hour

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Aims of Current Investigation

  • Consider Economical and Design Factors
  • Higher Temperatures?
  • Influence of pressure? (HIPing vs. VHT)
  • Develop structure property relationship for

tribo-mechanical applications

Methodology of Investigation

POWDER MANUFACTURE (WC-12%Co)

  • Agg. & Sint.

HVOF SPRAYING (JP5000) POST-TREATMENT HIPed (850 & 1200oC @ 150MPa for 1 hour) (Uncapsulated) Vacuum Heating @1200oC for 1 hour

  • Coating Microstructure (SEM, XRD)
  • Mechanical Strength (Modulus, Hardness)
  • Residual Stress using Neutron Diffraction
  • Sliding Wear Resistance (Ceramic and Metallic couples)
  • Rolling Contact Fatigue Testing
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Hot Isostatic Pressing Unit

FURNACE PRESSURE VESSEL WORK- PIECE

HIPing Conditions

No Encapsulation 4 °C /minute Heating /Cooling rate Argon Environment 150 MPa Pressure 850 °C , 1200 °C Temperature

SEM – As-sprayed vs. HIPed@850oC

As-Sprayed HIPed @850oC

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SLIDE 5

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10 20 30 40 50 60 70 80 90

  • W2C
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co2W4C
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C

XRD – As-sprayed vs. HIPed @850oC

10 20 30 40 50 60 70 80 90

  • W2C
  • W
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • W2C
  • W2C
  • W2C
  • W2C
  • W2C

Intensity (Counts/sec)

As-sprayed HIPed@850oC SEM – As-sprayed vs. HIPed or VHT @1200oC As-Sprayed HIPed or VHT

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XRD – As-sprayed vs. HIPed @1200oC

Intensity (Counts/sec) 10 20 30 40 50 60 70 80 90

  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C
  • Co6W6C

10 20 30 40 50 60 70 80 90

  • W2C
  • W
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • WC
  • W2C
  • W2C
  • W2C
  • W2C
  • W2C

As-sprayed HIPed@1200oC

  • Carbon diffusion

towards the substrate

  • Formation of

Kirkendall voids

  • Diffusion layer

HIPed @1200oC C coating WC Co substrate Co6W6C & C Fe Cr

  • Diffusion of Fe and Cr from

substrate

  • Carbide dissolution to form

prismatic faces

  • Free Carbon & eta-phases

As-sprayed Kirkendall voids Cr 7% Fe 19% Co 5% C 48% Diffusion layer W 21% At%

Microstructural Changes -Summary

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Residual Strain –Neutron Diffraction

  • 4000
  • 3000
  • 2000
  • 1000

1000 0.5 1 1.5 2 2.5 3 As-Sprayed coating HIPed coating

Depth from coating surface (mm) Microstrain coating substrate

As-sprayed HIPed@1200oC

Incident Beam

Diffracted beam Sample Detector 1 Detector 2 ISIS Facility Set-up, UK

Hardness Comparison

200 400 600 800 1000 1200 1400 1600 1800 2000 50 100 150 200 250 300 350 400 450

As-sprayed HIPed at 850C HIPed at 1200C Heat-treated

COATING SUBSTRATE Depth from surface Vickers Hardness (HV300)

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Indentation Modulus = E(1

E(1-

  • ν

ν2

2)

)

100 200 300 400 500 As-sprayed HIPed @ 850°C HIPed @ 1200°C Vacuum heat-treated @ 1200°C

I n d e n t a t i

  • n

M

  • d

u l u s ( G P a )

Sliding direction Sliding direction

Sliding Wear Tests Sliding Wear Tests

Reciprocating ball on plate apparatus Reciprocating ball on plate apparatus

Normal load Normal load

Ball Coating

Test conditions Test conditions

Dry Lubrication 0.012m/s Sliding Speed 12 and 22 N Load 440C Steel Si Si3

3N

N4

4 ceramic

ceramic Counter Body (balls)

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Wear Performance - system

10 20 30 40 50 60 70 80

As-sprayed HIPed at 850C HIPed at 1200C Heat-treated

steel - 12N steel - 22N ceramic - 12N ceramic - 22N

Wear resistance (Nm/mm3)

Coating

Drive shaft connected via belt to motor rotates coated disc at 4000 rpm

Air pressure from bellows generates required contact load between balls and disc.

45o

0.5a

Maximum shear stress

Substrate

2a Hertzian Contact Width

Rolling Contact Fatigue Tests

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10

Full Film Lubricant Boundary Regime 2.7 GPa Hertzian Contact Stress 25 ºC Temperature Steel / Ceramic Planetary Balls

RCF Test Conditions RCF Test Results

1 2 3 4 As-sprayed HIPed @ 850°C HIPed @ 1200°C Vacuum heat-treated @ 1200°C Steel, 2.7GPa Ceramic, 2.7GPa

Stress cycles (×106)

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RCF Failure Modes

Micro-cracks WEAR TRACK

HIPed@1200oC Progressive and Predictable Failure Vacuum heated@1200oC Catastrophic Failure

Post RCF Test Analysis

200 (µm) 200 (µm) as-sprayed HIP 1200ºC 40µm 20µm

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Conclusions

1. Microstructural changes associated with the post-treatment of WC-Co coatings can significantly improve tribo-mechanical performance of components by improving the hardness (phase changes), cohesive strength (interlamellar bonding) and adhesive strength (diffusion zone)

  • f coatings.

2. Improvement in RCF performance was attributed to the diffusion at the coating substrate interface resulting in metallurgical bonding. 3. Sliding wear test results indicate that the overall wear resistance improves with the post-treatment, and best results were obtained for coatings HIPed at 850oC for ceramic and at 1200oC for steel counterbody. 4. Residual stress investigations confirmed that not only the post-treated coatings have lower and more uniform compressive strain, but also the strain gradient at the coating substrate interface is minimised after the post-treatment.

Acknowledgements

  • S. Davies at Bodycote HIP, UK (HIPing)
  • Prof. S. Tobe at Ashikaga Institute, Japan

for EPMA analysis

  • ISIS (Rutherford Lab, UK) for use of

neutron diffraction facilities

  • EPSRC, UK for financial contribution