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Corrosion Testing of HVOF Thermal Spray Coatings

Corrosion Testing of HVOF Thermal Spray Coatings. By: Stephen P. Gaydos Boeing – St. Louis 20 February 2002. Chrome Plate Baseline. #1 Problem is QQ-C-320 Has No Corrosion Resistance Requirement Ferroxyl Porosity Test (Allows 15 pits/150 sq.in.) Why No Corrosion Testing In QQ-C-320?

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Corrosion Testing of HVOF Thermal Spray Coatings

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  1. Corrosion Testing of HVOF Thermal Spray Coatings By: Stephen P. Gaydos Boeing – St. Louis 20 February 2002

  2. Chrome Plate Baseline • #1 Problem is QQ-C-320 • Has No Corrosion Resistance Requirement • Ferroxyl Porosity Test (Allows 15 pits/150 sq.in.) • Why No Corrosion Testing In QQ-C-320? • Chrome Plate Contains Cracks and Porosity and Could Not Pass a Corrosion Test • Chrome Plate Appears to Work O.K. in Severe Service Environments So Corrosion Testing Never Added as Requirement

  3. HVOF Corrosion Testing • What Criteria Do You Use for HVOF? • Can’t Use QQ-C-320 So Create Your Own • Put in Salt Spray and Look for Red Rust (Most Popular Criteria Being Used) • Tells You if You Have Base Metal Corrosion • Put in Salt Spray and Look For Any Signs of Corrosion – Base Metal or Coating • Currently Under Investigation • Conduct Electrochemical Testing • Potentiodynamic, Potentiostatic, EIS, etc.

  4. HVOF Sample Prep • 1018 Steel - 1” O.D. Bar • Grit Blast • Apply per BAC 5851 • St. Louis Metallizing • SM Diamond Jet & TAFA JP5000 • Powders - WC-17Co • SM 2005 (Normal) & 2006 (Fine) • TAFA 1343VM (Normal) & 1343VF (Fine)

  5. HVOF Sample Prep (Cont.) • Powders - WC-10Co-4Cr • SM 5847 • TAFA 1350VM • Thickness 3 to 5 mils • As Sprayed and Ground to 8 micro inch • Sealers • Metco Seal AP and URS

  6. Chrome Plate Prep • 1018 Steel - 1” O.D. Bar • Grit Blast • Chrome Plate per PS 13102 (QQ-C-320) • 2 to 3 mils thick • Two Different Plating Vendors Used • Optional Ni Underplate Applied At 1.5 mils • As Plated (No Grinding) • Sealers • Metco Seal AP or URS • IMPCO RC-80 per PS 11501

  7. HVOF Specimen Prep

  8. HVOF Test Specimens (Before) TAFA/1350VM/8uin DJ/5847/8uin

  9. Corrosion Tests • Salt Spray Tests • ASTM B117 - Neutral Salt Spray • ASTM G85 - SO2 Salt Spray • Electrochemical Tests • Determine Corrosion Rates (mils per year) • Potentiodynamic • EIS

  10. Salt Spray Test Results

  11. 5% NaCl Salt Spray Results for Chrome Plating Cr Plate 2 Weeks = Cr Plate 2 Days = Cr* Plate 1 Week = Cr* Plate 2 Weeks = *Cr Plate Vendor #2

  12. SO2 Salt Spray Results for Chrome Plating 1 Week for Cr* Plate 2 Days for Cr Plate *Cr Plate Vendor #2

  13. Salt Spray Results for Ni/Cr Plating 30 Days in 5% NaCl Salt Spray 30 Days in SO2/NaCl Salt Spray

  14. 5% NaCl Salt Spray Results for HVOF Coatings 4 Week Exposure = For WC-Co TAFA/1343VM/8uin TAFA/1343VF/8uin DJ/2005/8uin DJ/2006/8uin 4 Week Exposure For = WC-Co-Cr DJ/5847/8uin TAFA/1350VM/8uin

  15. SO2 Salt Spray Results for HVOF Coatings Two Day Exposure = For WC-Co TAFA/1343VM/8uin TAFA/1343VF/8uin DJ/2005/8uin DJ/2006/8uin One Week Exposure For = WC-Co-Cr TAFA/1350VM/8uin DJ/5847/8uin

  16. Electrochemical Test Results

  17. *Cr Plate Vendor #2

  18. *Cr Plate Vendor #2

  19. *Different Cr Plate Source

  20. Conclusions • Not All Chrome Plate Behaves The Same In Corrosion Tests • Sealing Helps Chrome Plate But Does Not Appear to Help HVOF Coatings • HVOF WC-10Co-4Cr Has Better Corrosion Resistance Than WC-17Co • Nickel Underplate With Chrome Plating Has Superior Corrosion Resistance

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