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 SteelAtmospheric Exposure For 3 Years

Before Cleaning

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

After Cleaning

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

Before Cleaning

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

After Cleaning

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

HVOF and Hard Chrome on 7075 AluminumAtmospheric Exposure for 3 Years

Before Cleaning

Pits

HVOF and Hard Chrome on 7075 AluminumAtmospheric Exposure For 3 Years

After Cleaning

Pits

HVOF and Hard Chrome on 7075 AluminumAtmospheric Exposure for 3 Years

Before Cleaning

Pits

HVOF and Hard Chrome on 7075 AluminumAtmospheric Exposure For 3 Years

After Cleaning

Pits

HVOF and Hard Chrome on 7075 AluminumAtmospheric Exposure For 3 Years

After Cleaning

Pits

PROTECTION RATINGS FOR 4 MIL COATINGS OVER 7075 ALUMINUM (PLATES)

0 2 4 6 8 10 12

WC/Co *

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

(edges epoxy-masked)

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.