Atmospheric Corrosion Testing
Comparison of Electrodeposited Hard Chrome
to HVOF WC/17Co and Tribaloy 400
Three-Year Atmospheric Exposure
Exposures Conducted at
Naval Research Laboratory
Marine Corrosion Test Facility, Key West, FL
Report Prepared by Paul Natishan and Bruce Sartwell
Naval Research Laboratory
Atmospheric Corrosion Testing
Substrate Materials: 4340 steel and 7075-T73 aluminum alloy
Substrate Preparation: For EHC, grit blast with 180-220 grit Al2O3
For HVOF, grit blast with 54 grit Al2O3
Coating Deposition:
EHC deposited at NADEP Jacksonville following MIL-STD-1501; on 7075
alloy, 0.0015-inch-thick sulfamate Ni deposited prior to Cr
WC/17Co deposited at NADEP Jacksonville using hybrid Diamondjet gun,
hydrogen fuel, Diamalloy 2005 powder
Tribaloy 400 deposited at Southwest Aeroservice 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
Before Cleaning
HVOF and Hard Chrome Coatings on 4340 Steel
Atmospheric Exposure For 3 Years
After Cleaning
HVOF and Hard Chrome Coatings on 4340 Steel
Atmospheric Exposure For 3 Years
Before Cleaning
HVOF and Hard Chrome Coatings on 4340 Steel
Atmospheric Exposure For 3 Years
After Cleaning
PROTECTION RATINGS FOR 4 MIL COATINGS OVER 4340 STEEL (PLATES)
Edge
Hard Chrome, with nickel
sublayer
Face
Triballoy 400 **
WC/Co *
0
2
4
6
8
Protection Ratings (10 = Best)
** "T-400" (Stellite): 60% Co, 28% Mo, 9% Cr, 3% Si
* Diamalloy 2005 (Sulzer-Metco): 83%WC, 17% Co
10
12
HVOF and Hard Chrome on 7075 Aluminum
Atmospheric Exposure for 3 Years
Before Cleaning
Pits
HVOF and Hard Chrome on 7075 Aluminum
Atmospheric Exposure For 3 Years
After Cleaning
Pits
HVOF and Hard Chrome on 7075 Aluminum
Atmospheric Exposure for 3 Years
Before Cleaning
Pits
HVOF and Hard Chrome on 7075 Aluminum
Atmospheric Exposure For 3 Years
After Cleaning
Pits
HVOF and Hard Chrome on 7075 Aluminum
Atmospheric Exposure For 3 Years
After Cleaning
Pits
PROTECTION RATINGS FOR 4 MIL COATINGS OVER 7075 ALUMINUM
(PLATES)
Hard Chrome, with nickel
sublayer
Edge
Face
Triballoy 400 **
WC/Co *
(edges epoxy-masked)
WC/Co *
0
2
4
6
8
Protection Ratings (10 = Best)
** "T-400" (Stellite): 60% Co, 28% Mo, 9% Cr, 3% Si
* Diamalloy 2005 (Sulzer-Metco): 83%WC, 17% Co
10
12
Summary
1. On 4340 steel, the HVOF WC/Co coating outperformed the
EHC and HVOF T-400 coatings.
2. On 7075 aluminum, in general the EHC coating performed
best.
3. On 7075 aluminum, two samples of a smaller dimension (3 x
4 inches) had protection ratings that were better than the
EHC coatings on the 4 x 6 inch samples.
4. Some general corrosion of the WC/Co coatings was
observed.