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 Steel Atmospheric Exposure For 3 Years Thickness 0.004”, Coatings Not Ground

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 Testing 4340 rods Coating 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.

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

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

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

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

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.

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.

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

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

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

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.

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.

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.