HCAT – TORONTO September 24-26, 2002 1 Nihad Ben Salah, M&P Héroux Devtek Inc.- Landing Gear...

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HCAT – TORONTOSeptember 24-26, 2002

Nihad Ben Salah, M&P

Héroux Devtek Inc.- Landing Gear DivisionENG/R&D - Longueuil, Québec (Canada)

FINISHING, FLUID COMPATIBILITY AND NDT

INSPECTION OF HVOF COATING

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Introduction

Progress Producibility: Finishing, fluid compatibility

and NDT on WC-10Co-4Cr HVOF coating

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HCAT – TORONTOSeptember 24-26, 2002Progress/ Producibility

Testing Chemical stripping: 100% achieved (see

previous presentations). Final report about to be released

Finishing and superfinishing – 80% achieved, Narrowing the optimum grinding parameters window for a better productivity

Fluid compatibility: Corrosion tests achieved – Hydrogen embrittlement in progress

NDT : MPI, FPI, Barkhausen Noise Inspection on finished parts

All tests should be finished by March 2003

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HCAT – TORONTOSeptember 24-26, 2002Finishing – ”Rough” previous

Results

Higher wheel speed improves the finish (5000 to 7000 SFM) “High work speed with low crossfeed improves the finish and decreases the total time of grinding” BUT… Optimum infeed seems to be around 0.0002 in. Higher infeed decreases the finish and damage the coating. Lower grit (bigger abrasive particles) decreases productivity. The required finish is obtained after a longer time of grinding. For the same time, finish is better for higher grit, BUT…

Samples: 4inch OD x 12inch L

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HCAT – TORONTOSeptember 24-26, 2002Finishing –New results &

Interpretation

A good finish does not mean a good coating (FPI results)Most of the used grinding parameters did not damage the steel substrate (100% BNI). Concerns are raised when using higher grit wheel with inappropriate wheel speed and infeed.Higher wheel speed improves the finish but affect the coating integrity.When using higher grit, thickness control is betterFor a better control of the integrity of the coating (quality and thickness) it is safer to target an average finish after grinding and improve it by superfinishing

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HCAT – TORONTOSeptember 24-26, 2002Superfinishing -

Results

For these tests, 2µinch Ra and 95-99% Bearing Ratio were typical super-finish characteristics of WC-Co-Cr reached.

The stone gives a fuzzy and “less cosmetic” finish The ribbon gives the best cosmetic finish Pressure and work speed shall be higher when using paste

and ribbon, and the minimum when using the stone To have a better cosmetic finish, the two last passes

should be done without vibration. No need to have very high finish as starting point for

superfinishing

Abrasive used : Diamond (paste, stone, ribbon)

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Abusive Grinding

Grinding:*Small samples of Aermet 100, OD 0.625inch, ID0.440 inch

*No cooling fluidTests: *Metallographic preparation per ASTM E1920 and Buehler Tech-note

*Micro-hardness profile *Cross section SEM observations

Coating: Spalling, delamination, cracks, affected microstructureSubstrate : Heat affected thickness of the substrate varies from 12 to 40 mils. Overheating could be high enough to decrease Aermet 100 hardness to 50 HRC.

DO NOT UNDERESTIMATE ABUSIVE GRINDING

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HCAT – TORONTOSeptember 24-26, 2002Abusive Grinding/SEM

Observations

Crack

Inequal thickness due to abusive grinding

(B)

(A)

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Bad Surface finish

Abusive Grinding/SEM Observations

Abusive grinding seems to have affected the microstructure of

the coating

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HCAT – TORONTOSeptember 24-26, 2002Abusive Grinding/SEM

Observations

DelaminationCrack

Crack preceding spalling in Area (A)

Delamination observed in Area

(B)

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HCAT – TORONTOSeptember 24-26, 2002Abusive Grinding/Micro-hardness

profile

Aermet 100 Base Metal- Area with thinner coating (A)

400

600

800

1000

1200

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Distance (inch)

Mic

ro-H

ard

nes

s V

icke

rs,

HV

300

Average Hardness 650 Hv : 58HRC


HVOF coating thickness < 1mils

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HCAT – TORONTOSeptember 24-26, 2002Abusive Grinding/Micro-hardness

profile

Aermet 100 Base Metal- Area with thicker coating (B)

400

600

800

1000

1200

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Distance (inch)

Mic

ro-h

ard

nes

s (H

v300

)

Aermet 100 hardness decrease at the interface with the coating- 50.5 HRC

HVOF coating thickness=2mils



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Calibration for maximum response of BNI with HVOF WC-Co-Cr coating and different substrates (4340, 300M and Aermet 100)

NDT- Barkhausen Noise

Calibration for burns detection OK

Set-up for Barkhausen Noise Inspection (BNI)

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HCAT – TORONTOSeptember 24-26, 2002NDT- Barkhausen Noise-Set up

(1)

MP decreases when HVOF coating or Cr plating thickness increases

MP decreases less drastically with HVOF coating thickness than with Chrome

BNI Vs Thickness - GAIN=50 MAGN=70

40

60

80

100

120

140

0 2 4 6 8 10

Thickness (mils)

Bar

khau

sen

Noi

se (M

P)

Chrome

HVOF WC-Co-Cr

Substrate: 4340 HT 260-280 ksi

Axial sensor

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Different calibration is needed for different substrates.

BN signal is the lowest for 300M0

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20

30

4050

60

70

80

90

0 20 40 60 80 100

MAGN

Bark

haus

en N

oise

(MP) 300M Bare

4340 Bare

Aermet 100

NDT- Barkhausen Noise-Set up (2)

Circumferential sensor

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Burns in the substrate are easily detected through HVOF coating on calibration test pieces

Calibration with coating is optimum for shot peening effect detection on calibration test pieces


020406080

100120140

0 20 40 60 80 100

MAGN

MP

Shot peen No shot peen

HVOF Coating on SP surface HVOF coating on burned surface

Gain=50

Axial sensor

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Cracks in the substrate that are not linked with overheating cannot be detected by the RollScan


BNI calibration on cracked 4340 test piece at different MAGN level with the circumferential probe far from the crack and near the crack

(GAIN=25)

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

0 20 40 60 80 100

MAGN

Ba

rkh

au

sen

No

ise

(B

N)

Far from the crack

On the crack

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Types of imperfections observed on the HVOF coating: cracks, pull-out, pits, porosities, “spiralling”

Warning: Some defects are only detected by visual inspection of ground HVOF with Neon light - Could not be detected by FPI.

These defects are more detectable in the ground condition than in the superfinished

Method used for chrome (per ASTM E1417) type I, Method C, sensitivity level 3 is more sensitive than the method used for Aluminum Method A.

On going: FPI, method C with higher sensitivity (level 4: Ultrahigh), MPI

NDT Inspection of the coating

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HCAT – TORONTOSeptember 24-26, 2002NDT- Visual

Visual Neon light observed defects: Pull out of HVOF coating

These defects are rarely detected by FPI

“Indents”Pull-out

Pull-out

Pull-out

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NDT- FPI

Best finish after grindingRa=6µinch, tp=57% visual after SF

Worst finish after grindingRa= 19-22 µinch, tp=0%Visual after SF

240R75 wheel7000/575

120R75 wheel

4500/100 6500/200

No pull-out observed

After SF: Ra= 2-3 µinch, tp= 90-99%

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NDT- FPIFPI detectable defects

« pits »

« Spiralling » associated with some pull-out not visible here

Ra=7Tp=28%

« Spiralling » not associated with pull-out

Porosities?

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NDT

What are « defects » in the HVOF after grinding?

What should the FPI/MPI operators reject?

Acceptance and rejection criteria should be defined

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HCAT – TORONTOSeptember 24-26, 2002Fluid Compatibility-

Tests

Organic and semi-organic solutions (Immersion tests at room and high temperature)

Corrosion preventive products Greases Hydraulic fluids Grease + hydraulic fluids Degreasers

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HCAT – TORONTOSeptember 24-26, 2002Fluid Compatibility-

Tests Aqueous Solutions : Tafel plots for solutions

used by immersion, Cyclic Voltametry for solutions used with applied potential to determine dissolution rates. Tests were done on freshly prepared and used (from the shop) solutions at IMI (NRC)

Cleaning solutions Inspection related products (FPI, MPI, nital

etch) Plating and stripping solutions

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Fluid Compatibility- Tests

Aqueous Solutions : Hydrogen Embrittlement susceptibility in all previous solutions.

Notched specimens for H2 embrittlement type 1a (standard) per ASTM F-519, uncoated notch (keep the test valid per Spec. + simulate any possible galvanic corrosion), Load 75% NTS

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Fluid Compatibility (Results)

1- None of the organic tested fluid in the given conditions reacted with the HVOF coating: No Thickness change No Weight change No Finish change No visual modification

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Fluid Compatibility (Results)2- Aqueous solutions:No relevant dissolution rate observed on any tested solution used by immersion (higher rate 0.008 mils/h in the Mn phosphate solution)Plating solutions are harmless in term of dissolution because the process is cathodic (0.003 mils/h)Oakite cleaning solution, anodic process could be a problem, voltametic curves show a possible high dissolution rate after 5 minutes of immersion (0.5 mils/h)

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(Solutions tested so far: Cleaning solutions and nital etch)

Fluid Compatibility/Hydrogen

Embrittlement

nb of specimens Solution Immersion time (minutes) Bake Life (hrs) Status2 (base line) None - - 200 2 pass

4 Nitric acid 3 yes/ 4 hours 1h30 Fail at the notch4h30 Fail at the notch

58h30 Fail at the notch1h30 Fail at the notch

4 Nitric acid 3 No 2 Fail at the notch95 (?) Fail at the notch

Results not Available4 Oakite 3 No 148 Fail at the notch

54h30 Fail at the notchResults not Available

4 B&B Spray-it-in 20 No 33 Fail at the notch95(?) Fail at the notch

Results not Available

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HCAT – TORONTOSeptember 24-26, 2002Fluid

Compatibility/Hydrogen Embrittlement

Recommandations:1) Increase when possible the baking temperature or the

duration2) Process HVOF coating after any plating operation when

possible

Possible interpretation:1) HVOF coating could be a barrier for hydrogen removal2) Cleaning solutions/steel/HVOF coating: Galvanic cell?

On going:1) Tests in all plating solutions2) Tests with increasing baking time3) Repeat tests on cleaning solutions4) SEM observations of failed specimens

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How the notch looks like when the whole specimen is HVOF coated

Fluid Compatibility/Hydrogen

Embrittlement

HCAT – TORONTO September 24-26, 2002 1 Nihad Ben Salah, M&P Héroux Devtek Inc.- Landing Gear...

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Transcript of HCAT – TORONTO September 24-26, 2002 1 Nihad Ben Salah, M&P Héroux Devtek Inc.- Landing Gear...