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HCAT – TORONTO September 24-26, 2002 1 Nihad Ben Salah, M&P Héroux Devtek Inc.- Landing Gear Division ENG/R&D - Longueuil, Québec (Canada) FINISHING, FLUID.

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Presentation on theme: "HCAT – TORONTO September 24-26, 2002 1 Nihad Ben Salah, M&P Héroux Devtek Inc.- Landing Gear Division ENG/R&D - Longueuil, Québec (Canada) FINISHING, FLUID."— Presentation transcript:

1 HCAT – TORONTO September 24-26, Nihad Ben Salah, M&P Héroux Devtek Inc.- Landing Gear Division ENG/R&D - Longueuil, Québec (Canada) FINISHING, FLUID COMPATIBILITY AND NDT INSPECTION OF HVOF COATING

2 HCAT – TORONTO September 24-26, Introduction Progress Producibility: Finishing, fluid compatibility and NDT on WC-10Co-4Cr HVOF coating

3 HCAT – TORONTO September 24-26, Progress/ 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

4 HCAT – TORONTO September 24-26, Finishing – 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 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

5 HCAT – TORONTO September 24-26, Finishing –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 better For 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

6 HCAT – TORONTO September 24-26, Superfinishing -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)

7 HCAT – TORONTO September 24-26, Abusive Grinding Grinding:*Small samples of Aermet 100, OD 0.625inch, ID0.440 inch *No cooling fluid Tests: *Metallographic preparation per ASTM E1920 and Buehler Tech-note *Micro-hardness profile *Cross section SEM observations Coating: Spalling, delamination, cracks, affected microstructure Substrate : 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

8 HCAT – TORONTO September 24-26, Abusive Grinding/SEM Observations Crack Inequal thickness due to abusive grinding (B) (A)

9 HCAT – TORONTO September 24-26, Bad Surface finish Abusive Grinding/SEM Observations Abusive grinding seems to have affected the microstructure of the coating

10 HCAT – TORONTO September 24-26, Abusive Grinding/SEM Observations Delamination Crack Crack preceding spalling in Area (A) Delamination observed in Area (B)

11 HCAT – TORONTO September 24-26, Abusive Grinding/Micro-hardness profile

12 HCAT – TORONTO September 24-26, Abusive Grinding/Micro-hardness profile

13 HCAT – TORONTO September 24-26, Calibration for maximum response of BNI with HVOF WC-Co-Cr coatingCalibration 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)

14 HCAT – TORONTO September 24-26, NDT- 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 Axial sensor

15 HCAT – TORONTO September 24-26, Different calibration is needed for different substrates. BN signal is the lowest for 300M NDT- Barkhausen Noise-Set up (2) Circumferential sensor

16 HCAT – TORONTO September 24-26, 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 NDT- Barkhausen Noise-Set up (3) Gain=50 Axial sensor

17 HCAT – TORONTO September 24-26, Cracks in the substrate that are not linked with overheating cannot be detected by the RollScan NDT- Barkhausen Noise-Set up (4)

18 HCAT – TORONTO September 24-26, 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

19 HCAT – TORONTO September 24-26, NDT- Visual Visual Neon light observed defects: Pull out of HVOF coating These defects are rarely detected by FPI Indents Pull-out

20 HCAT – TORONTO September 24-26, NDT- FPI Best finish after grinding Ra=6µinch, tp=57% visual after SF Worst finish after grinding Ra= µinch, tp=0% Visual after SF 240R75 wheel 7000/ R75 wheel 4500/ /200 No pull-out observed After SF: Ra= 2-3 µinch, tp= 90-99%

21 HCAT – TORONTO September 24-26, NDT- FPI FPI detectable defects « pits » « Spiralling » associated with some pull-out not visible here Ra=7 Tp=28% « Spiralling » not associated with pull-out Porosities?

22 HCAT – TORONTO September 24-26, NDT What are « defects » in the HVOF after grinding? What should the FPI/MPI operators reject? Acceptance and rejection criteria should be defined

23 HCAT – TORONTO September 24-26, Fluid Compatibility- Tests Organic and semi-organic solutions (Immersion tests at room and high temperature) Corrosion preventive products Greases Hydraulic fluids Grease + hydraulic fluids Degreasers

24 HCAT – TORONTO September 24-26, Fluid 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

25 HCAT – TORONTO September 24-26, Fluid Compatibility- Tests Aqueous Solutions : Hydrogen Embrittlement susceptibility in all previous solutions. Notched specimens for H 2 embrittlement type 1a (standard) per ASTM F-519, uncoated notch (keep the test valid per Spec. + simulate any possible galvanic corrosion), Load 75% NTS

26 HCAT – TORONTO September 24-26, 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

27 HCAT – TORONTO September 24-26, Fluid Compatibility (Results) 2- Aqueous solutions: No relevant dissolution rate observed on any tested solution used by immersion (higher rate 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)

28 HCAT – TORONTO September 24-26, (Solutions tested so far: Cleaning solutions and nital etch) Fluid Compatibility/Hydrogen Embrittlement

29 HCAT – TORONTO September 24-26, Fluid Compatibility/Hydrogen Embrittlement Recommandations: 1)Increase when possible the baking temperature or the duration 2)Process HVOF coating after any plating operation when possible Possible interpretation: 1)HVOF coating could be a barrier for hydrogen removal 2)Cleaning solutions/steel/HVOF coating: Galvanic cell? On going: 1)Tests in all plating solutions 2)Tests with increasing baking time 3)Repeat tests on cleaning solutions 4)SEM observations of failed specimens

30 HCAT – TORONTO September 24-26, How the notch looks like when the whole specimen is HVOF coated Fluid Compatibility/Hydrogen Embrittlement


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