Copper/Nickel Alloy Plating is Brittle

A. Hi Maurice!

Copper and nickel form a solid solution completely across the phase diagram- they don't form any weird crystal structure or intermetallic compound that would account for any brittleness. I wouldn't think that would happen, so I agree with your surprise that it is!

If I were faced with this problem internally, I'd examine the broken plating chips with my SEM, looking for intergranular fracture- and if I found it I'd try to see what was on the grain boundaries that might make the plating fracture there. I normally wouldn't consider hydrogen, since it shouldn't embrittle copper as it does steel, but I'd keep it in mind as a convenient scapegoat. I'd use the EDS part of the SEM to look for other elements, but EDS is only going to find them if they are say, more than 1%. It's certainly possible something like selenium or arsenic might be on the grain boundaries, embrittling them, and I'd never see it.

I'd also mount and polish a sample, and look at it metallographically, as those are the tools readily available in our lab. That would show what geometry grains I was getting- long, or blocky, or equiaxed, etc- and that might shed some light on the issue.

If you want to send me a sample, I'll take a quick look. Ted has my contact info, but I'm not hard to find anyway.

Good luck!

Lee Gearhart metallurgist East Aurora, New York