Cobalt electroplating over nickel-plated steel
in the past cobalt was used as a brighterner for Nickel plating electrolyites, now since Cobalt is about 5 times more expensive than Nickel, is hardly used but you can add about 30 grams per litter of CoSO4 to your regular nickel plating solution and you will end up with a Nickel/Cobalt alloy that is stronger and whiter than plain Nickel, also keep in mind that in these type of baths Cobalt plates out faster than Nickel, that means that a 10% Cobalt Sulfate(90% Nickel Sulfate) plating bath will produce about a 70% Nickel/ 30% Cobalt alloy plating.