1. Corrosion Testing Acknowledgements to:
Paul Natishan, Rick Foster, CAPT Marty Mahon
Center for Corrosion Science & Engineering
Naval Research Laboratory
Washington, DC and Key West, FL

2. Atmospheric Corrosion Testing
Substrate Materials: steel
Substrate Preparation: For EHC, grit blast with grit Al2O3
For HVOF, grit blast with 54 grit Al2O3
Coating Deposition:
EHC deposited following MIL-STD-1501
WC/17Co deposited using hybrid Diamondjet gun, hydrogen fuel, Diamalloy 2005 powder
Tribaloy 400 deposited using Jet Kote II, hydrogen fuel, Stellite T-400 powder
Coating thicknesses of inches
Tested as-deposited (no grinding)
Epoxy masking used on non-coated surfaces

3. HVOF and Hard Chrome Coatings on 4340 Steel
Atmospheric Exposure For 3 Years
Thickness 0.004”, Coatings Not Ground

5. Additional Corrosion Testing
To address significant discrepancy between previous B117 and atmospheric testing on flat plates, and LG B117 testing on rods, additional B117 corrosion tests were conducted as follows:
Substrate Materials: 4340 rods, 1” diameter, 6” long
4340 plates, 3” x 4” x 3/16”
300M rods, 1” diameter, 6” long
Coatings: WC/17Co, WC/10Co4Cr, EHC
On rods, coatings to be applied on curved surface, terminating 1” from one end and 1/4” from other end (length of coating 4-3/4 inches)
On plates, only coat one face 3”-wide dimension coated edge-to-edge, on 4”-wide dimension, coating to terminate 1/2-inch from edge (coated area is 3” x 3”)
Deposition parameters to match Landing Gear JTP, plus must follow Boeing Spec. Sheet 160T1000 which requires that HVOF coatings not terminate with a square edge, but shall taper from full to zero thickness over a minimum length of inches
EHC coatings ground to 16 Ra finish; some HVOF coatings ground to 8 Ra
Non-coated areas to be cadmium plated (including chromate conversion coating) with slight overlap of EHC and HVOF coating

6. Additional Corrosion Testing
4340 rods
Coating Thickness Ground Spray Co. # of samples
WC/Co ” Y Hitemco
WC/Co ” Y Southwest
WC/Co ” N H
WC/Co ” N S
WC/Co ” Y H
WC/Co ” Y S
WC/CoCr ” Y H
WC/CoCr ” Y S
WC/CoCr ” N H
WC/CoCr ” N S
WC/CoCr ” Y H
WC/CoCr ” Y S
EHC ” Y S
EHC ” Y S
Total
Repeat this exact matrix for the 4340 plates and the 300M rods.

7. WC/Co coatings (ground) on 300M steel.
breached
coating
August 2000
August 2001
WC/Co coatings (ground) on 300M steel.

8. WC/Co coatings (ground) on 4340 steel.
breached
coating
August 2000
August 2001
WC/Co coatings (ground) on 4340 steel.

9. Comparison of hard chrome samples.
breached
coating
August 2000
August 2001
Comparison of hard chrome samples.

12. WC/Co coatings (3 mil) on 4340 steel.
general
corrosion
breached
coating
unground
ground
WC/Co coatings (3 mil) on 4340 steel.

13. Comparison of HVOF and EHC coatings on 4340 steel.
general
corrosion
WC/Co
ground
10 mil
EHC
ground
10 mil
WC/Co-Cr
ground
10 mil
Comparison of HVOF and EHC coatings on 4340 steel.

14. Comparison of HVOF and EHC coatings on 300M steel.
general
corrosion
WC/Co
ground
10 mil
EHC
ground
10 mil
WC/Co-Cr
ground
10 mil
Comparison of HVOF and EHC coatings on 300M steel.

15. WC/Co coatings (3 mil) on 300M steel.
general
corrosion
general
corrosion
breached
coating
unground
ground
WC/Co coatings (3 mil) on 300M steel.

16. WC/Co coatings on 4340 steel.
general
corrosion
breached
coating
ground
3 mil
ground
10 mil
WC/Co coatings on 4340 steel.

17. WC/Co coatings on 300M steel.
general
corrosion
general
corrosion
breached
coating
ground
3 mil
ground
10 mil
WC/Co coatings on 300M steel.

18. Comparison of HVOF and EHC coatings on 4340 steel.
general
corrosion
EHC
10 mil
WC/Co
ground
10 mil
Comparison of HVOF and EHC coatings on 4340 steel.

19. Comparison of HVOF and EHC coatings on 300M steel.
general
corrosion
EHC
10 mil
WC/Co
ground
10 mil
Comparison of HVOF and EHC coatings on 300M steel.

20. SUMMARY OF CORROSION TESTING
10 mil thick coatings fared better than 3 mil coatings of any composition in protecting the substrate.
The company applying the coating does not have a measurable, definitive effect on coating performance (given the small sample set).
Salt fog cabinet used at Kennedy Space Center appeared to be slightly more aggressive than one used at Naval Research Laboratory
EHC coatings outperform all other coating compositions, regardless of thickness in this year’s B117 test.
At 10 mil thickness, the data set infers WC/CoCr coatings show improved performance over WC/Co coatings, though one 10 mil WC/Co-Cr coating was breached.