Corrosion Testing of HVOF Thermal Spray Coatings

By: Stephen P. Gaydos Boeing – St. Louis 20 February 2002 1

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 2 2

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.

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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) 4 4

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 5 5

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 6 6

HVOF Specimen Prep

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HVOF Test Specimens (Before)

DJ/5847/8uin 8 TAFA/1350VM/8uin 8

Corrosion Tests

Salt Spray Tests  ASTM B117 - Neutral Salt Spray  ASTM G85 - SO 2 Salt Spray Electrochemical Tests  Determine Corrosion Rates (mils per year)  Potentiodynamic  EIS 9 9

Salt Spray Test Results

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5% NaCl Salt Spray Results for Chrome Plating

Cr Plate 2 Days = Cr Plate 2 Weeks = Cr* Plate 1 Week = *Cr Plate Vendor #2 11 Cr* Plate 2 Weeks = 11

SO2 Salt Spray Results for Chrome Plating

2 Days for Cr Plate *Cr Plate Vendor #2 12 1 Week for Cr* Plate 12

Salt Spray Results for Ni/Cr Plating

30 Days in 5% NaCl Salt Spray 13 30 Days in SO2/NaCl Salt Spray 13

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

TAFA/1350VM/8uin 14 DJ/5847/8uin 14

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

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DJ/5847/8uin

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Electrochemical Test Results

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*Cr Plate Vendor #2 18 18

*Cr Plate Vendor #2 19 19

*Different Cr Plate Source 20 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 21 21