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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. Atmospheric Corrosion Testing. Substrate Materials: 4340 steel

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corrosion testing
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

atmospheric corrosion testing
Atmospheric Corrosion Testing

Substrate Materials: 4340 steel

Substrate Preparation: For EHC, grit blast with 180-220 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 0.004 inches

Tested as-deposited (no grinding)

Epoxy masking used on non-coated surfaces

slide3

HVOF and Hard Chrome Coatings on 4340 Steel

Atmospheric Exposure For 3 Years

Thickness 0.004”, Coatings Not Ground

additional corrosion testing
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 0.006 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

additional corrosion testing6
Additional Corrosion Testing

4340 rods

CoatingThickness GroundSpray Co.# of samples

WC/Co 0.003” Y Hitemco 2

WC/Co 0.003” Y Southwest 2

WC/Co 0.003” N H 2

WC/Co 0.003” N S 2

WC/Co 0.010” Y H 2

WC/Co 0.010” Y S 2

WC/CoCr 0.003” Y H 2

WC/CoCr 0.003” Y S 2

WC/CoCr 0.003” N H 2

WC/CoCr 0.003” N S 2

WC/CoCr 0.010” Y H 2

WC/CoCr 0.010” Y S 2

EHC 0.003” Y S 2

EHC 0.010” Y S 2

Total 28

Repeat this exact matrix for the 4340 plates and the 300M rods.

slide7

breached

coating

August 2000

August 2001

WC/Co coatings (ground) on 300M steel.

slide8

breached

coating

August 2000

August 2001

WC/Co coatings (ground) on 4340 steel.

slide9

breached

coating

August 2000

August 2001

Comparison of hard chrome samples.

slide12

general

corrosion

breached

coating

unground

ground

WC/Co coatings (3 mil) on 4340 steel.

slide13

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.

slide14

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.

slide15

general

corrosion

general

corrosion

breached

coating

unground

ground

WC/Co coatings (3 mil) on 300M steel.

slide16

general

corrosion

breached

coating

ground

3 mil

ground

10 mil

WC/Co coatings on 4340 steel.

slide17

general

corrosion

general

corrosion

breached

coating

ground

10 mil

ground

3 mil

WC/Co coatings on 300M steel.

slide18

general

corrosion

EHC

10 mil

WC/Co

ground

10 mil

Comparison of HVOF and EHC coatings on 4340 steel.

slide19

general

corrosion

EHC

10 mil

WC/Co

ground

10 mil

Comparison of HVOF and EHC coatings on 300M steel.

slide20

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.