Copper/Nickel Alloy Plating is BrittleJune 19, 2012
Q. I am developing a Copper/Nickel alloy (98.5% Cu, 1.5% Ni.) The starting chemicals are Copper Sulfate pentahydrate, Nickel Sulfate hexahydrate and Trisodium Citrate as the complexing agent for the co-deposition. So far I have achieved the correct composition, but the alloy is very brittle. I am using an insoluble anode and no additives (as yet).
Can you explain the cause of the brittleness and how to correct it. The pH of the mixture is approx. 4-5. I am doing a potentiostatic deposition and according to my CV scan, the potential I am using should not cause excessive Hydrogen evolution.
Does anyone have any suggestions how to solve this problem
Plating Consultant - Danbury, Connecticut, USA
July 21, 2012
Can someone help me with this problem? A response either way would be greatly appreciated.
Consulting - Danbury, Connecticut, USA
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.
August 12, 2012
A. Hi Maurice