Bad adhesion of hard chrome on stainless steel
We think we have problems with adhesion of hard chrome on AISI 316. The failure can be seen as small areas (0.1 - 1 cm2) with very high roughness. The rest of the chrome is perfect.
The procedure is
1. Cyanidic alkaline degrease at room temp. + rinse in water
2. Anodic etch in 65 wt % sulfuric acid at room temp., 10-20 A dm-2, 60 seconds.
3. Direct transfer to Wood nickel at room temp. (approx. 200 g/l nickel chloride, pH=0 adjusted with HCl), 2 V cathodic, 60 seconds + rinse in water
4. Hard chrome deposition (mixed catalyst), 100 µm, 55°C, 30 A dm-2, C.E approx. 15 %,
Our AISI 316 samples are turned and have a good and smooth surface.
We will try to replace the bath because we have heard that chloride contamination (from Wood nickel) may have an influence.
PLEASY REPLY, IF YOU HAVE AN OPINION ON THIS! WE THROW OUT 50 % OF OUR SAMPLES. SOMETIMES THE PRETREATMENT WORKS, SOMETIMES IT DOESNT.Lasse Christoffersen
Technical University of Denmark - Lyngby, Denmark
Just a few adjustments I would make:
1. Cyanidic alkaline degrease at 140 degrees F + rinse in water
2. Wood's Nickel Strike at room temp. (approx. 200 g/l nickel chloride, Do not try to adjust pH to 0, just add acid based on a titration), Plate at a current density instead of by voltage., 60- 180 seconds + rinse in water
3. Hard chrome deposition (mixed catalyst), 100 µm, 55°C, 30 A dm-2, C.E approx. 15 %
I am not sure that chrloride will cause adhesion problems but you can try to test your chromium solution by a Hull cell test to check for chlorides. Plate a Brass panel with nickel for 10 minutes, 2 amp and then plate for 3 minutes 10 amp chrome on top of the nickel. If your chromium solution is contaminated with chloride you will observe etching at the low current densities. To get rid of the chlorides, check the answers regarding chlorides in chrome at this web site.
One more thing, you have to determine whether the problem is related to the plating solution or to the pretreatment process. Try to plate another kind of stainless steel and see whether you still face adhesion problems. Try to plate steel ( skipping the strike nickel) to determine whether the stirke causes the problem ()Too much iron in the strike can etch the stainless). You will have to try and eleminate each of the pretreatment processes in order to detect the trouble maker.
chemical process supplier
An alternate to Toms suggestion, use periodic reverse in your cyanide cleaner at room Temp.
The sulfuric treatment seems aggressive.
With the minimum time in rinse tanks and between tanks, especially between tanks, your process should work. I think that the part is passivating, probably after the nickel strike, but it could be after the etch also.
Chloride affects the catalyst ratio. Since you are using a fluoride, I doubt if the chloride will have much effect until it gets quite high. When it does, you will have the affect of too much catalyst.James Watts
- Navarre, Florida
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