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

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

HVOF and Hard Chrome Coatings on 4340 SteelAtmospheric Exposure For 3 Years

Thickness 0.004”, Coatings Not Ground

PROTECTION RATINGS FOR 4 MIL COATINGS OVER 4340 STEEL (PLATES)

0 2 4 6 8 10 12

WC/Co *

Triballoy 400 **

Hard Chrome, with nickelsublayer

Protection Ratings (10 = Best)

Edge

Face

** "T-400" (Stellite): 60% Co, 28% Mo, 9% Cr, 3% Si* Diamalloy 2005 (Sulzer-Metco): 83%WC, 17% Co

Additional Corrosion TestingTo 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, EHCOn 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 Testing4340 rodsCoating Thickness Ground Spray 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.

August 2000 August 2001

breached coating

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

WC/Co coatings (ground) on 4340 steel.

August 2000 August 2001

breached coating

Comparison of hard chrome samples.

August 2000 August 2001

breached coating

Type 300M Metal Coating Appearance Ratings

0 2 4 6 8 10 12

WC/Co 3 Gr Hitem

WC/Co 3 Gr SWAero

WC/Co 3 UG Hitem

WC/Co 3 UG SWAero

WC/Co 10 Gr Hitem

WC/Co 10 Gr SWAero

WC/Co/Cr 3 Gr Hitem

WC/Co/Cr 3 Gr SwAero

WC/Co/Cr 3 UG Hitem

WC/Co/Cr 3 UG SWAero

WC/Co/Cr 10 Gr Hitem

WC/Co/Cr 10 Gr SWAero

EHC 3 Gr SWAero

EHC 10 Gr SWAero

Co

atin

g T

ype

Appearance Rating

Series2

Series1

Type 4340 Metal Coating Appearance Ratings

0 2 4 6 8 10 12

WC/Co 3 Gr Hitem

WC/Co 3 Gr SWAero

WC/Co 3 UG Hitem

WC/Co 3 UG SWAero

WC/Co 10 Gr Hitem

WC/Co 10 Gr SWAero

WC/Co/Cr 3 Gr Hitem

WC/Co/Cr 3 Gr SwAero

WC/Co/Cr 3 UG Hitem

WC/Co/Cr 3 UG SWAero

WC/Co/Cr 10 Gr Hitem

EHC 3 Gr SWAero

EHC 10 Gr SWAero

Co

atin

g T

ype

Appearance Rating

Series2

Series1

breached coating

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

unground ground

general

corrosion

Comparison of HVOF and EHC coatings on 4340 steel.

general

corrosion

WC/Coground10 mil

WC/Co-Crground10 mil

EHCground10 mil

Comparison of HVOF and EHC coatings on 300M steel.

general

corrosion

WC/Coground10 mil

EHCground10 mil

WC/Co-Crground10 mil

breached coating

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

unground ground

general

corrosion general

corrosion

WC/Co coatings on 4340 steel.

ground10 mil

ground3 mil

breached coating

general

corrosion

WC/Co coatings on 300M steel.

ground10 mil

ground3 mil

breached coating

general

corrosion

general

corrosion

Comparison of HVOF and EHC coatings on 4340 steel.

general

corrosion

EHC10 mil

WC/Coground10 mil

Comparison of HVOF and EHC coatings on 300M steel.

general

corrosion

EHC10 mil

WC/Coground10 mil

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.