Letter 26129

Economically getting chrome plating adhesion on Hastelloy and stainless steel  

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We have been chosen to hard chromium plate two materials; one is a stainless steel, and the other a nickel based Hastelloy. At this stage I don't know the exact compositions or final heat treated conditions, but I do know they are French alloys.

We trialled them by using the standard vapour degrease, grit blast and reverse sulphuric/hydrofluoric etch, but as we all know, some of these alloys can be very hard to properly activate. The result was no adhesion after chrome plating.

Next we tried using a nickel strike and flash sulphamate nickel plate in addition to the above, and it worked quite well. But we want to avoid using this to keep our costs down. Does anyone have a suggestion as to what cleaning and activation cycle we may employ that will give us the good adhesion required, without having to resort to the nickel underplating?

Trevor Rowlands
Materials & Processes Engineer - Melbourne, Victoria, Australia

Trevor,

Hastaloy is almost the same alloy like Inconel 648 and 718 thats is a very difficult alloy to plate on. I have describe a method for it in letter 12398. This method work for me.

Regards,

Anders Sundman     surface finishing engineer Sweden

Prep as you have, Light reverse current etch in chrome tank. Big hassle and expense is the big knife switch you will need.

Jon Quirt
- Minneapolis, MN

Trevor,

As a jobbing shop, I get hundreds of jobs that are "stainless" or "hastelloy". The thing that we find always works is a good hydrogen flush. If the alloy has a high chrome content(A bluish colour) then a light etch first, if a high nicklel content(a yollowish colour) then stright in the vat live. If your not sure of the voltage to flush, Start plating at lowest posiable voltage, and turn up untill you see the first bubbles appear, then turn up a 1/2 Volt every 5 minutes, to the plating speed. On some of the Hastelloys you have to raise the voltage above the plating voltage for a few seconds to 'strike' and start them plating.

Regards, Steve ;-)

PS. For practical demonstrotion send air tickets to.....

Steve Kelson
hard chrome plating - Cheshire, England

Would try activation H2SO4/HF using current 30-50 A/sq dm, and then as Mr Steve Kelson suggested.

Cair Shishani
aircraft maintenance - Abu Dhabi, UAE

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