Electrolytic and Electroless Nickel

Q. What are the main differences between electrolytic nickel and electroless nickel? Can one be substituted for the other in metal finishing? C.Q.

 

A. The two processes are very different and result in different deposit properties. In my travels as a consultant and instructor, I have come to realize that many people in our industry do not have a solid understanding of the differences. Here are some things to consider when comparing electrolytic and electroless nickel processes:

Electrolytic Nickel	Electroless Nickel
Non-uniform thickness of deposit. Thicknesses dependent on current density at different locations on part surface. Fixturing may be required if differences in thickness can not be tolerated. Thickness controlled by current density and time in tank.	Uniform thickness of deposits even on parts with a complex shape as long as the part is properly prepared. No current density issues. Thickness usually controlled by time in the tank.
Deposit is essentially pure nickel.	Deposit is a nickel/phosphorus alloy and does not have the same physical properties as electrolytic nickel.
Deposit has a microhardness in the range of 250–450 VHN.	Deposit has microhardness of 340–600 VHN. If deposit is heat treated, hardness can be increased to 1000–1150 VHN range.
Deposit tends not to have lubricity and non-galling properties.	Deposit has some inherent lubricity and non-galling properties.
Thin deposits are porous.	Deposits are less porous and give better barrier corrosion protection to ferrous materials.
Causes hydrogen absorption, a problem with high-strength steels.	Causes reduced hydrogen absorption estimated to be less than 20% of that caused by electrolytic nickel.

There are a number of different types of electrolytic and electroless nickel plating baths available.
 

Electrolytic Nickel Baths	Comments
Watts nickel	Typically formulated with nickel sulfate and nickel chloride. Usually contains additives to smooth and brighten the deposit. Stress-reducing agents are usually be required to reduce internal stress level of the deposit.
Bright Nickel	Similar to the Watts bath but with higher levels of brighteners. The brightener system usually contains two components. Bright nickel deposits cause problems with soldering and brazing.
Sulfamate nickel	This plating bath gives a very pure nickel deposit with minimal stress. The deposit can be soldered and brazed with a minimum amount of difficulty.
Black nickel	An attractive black finish primarily applied for decorative purposes. Depending on the thickness it can be shiny or matte in appearance.
Electroless Nickel	Comments
Low phosphorus (1–3% P)	Provides a hard deposit. With heat treatment, can obtain hardness values similar to hard chrome.
Medium phosphorus (6–8% P)	Most commonly found EN bath. Very good corrosion protection if properly applied.
High phosphorus (12–13% P)	Provides greatest amount of corrosion protection. An excellent coating for parts exposed to an acidic environment. Also used in the electronics industry. Solderability decreases rapidly after parts are removed from the plating bath.
Electroless Nickel Composites	Teflon (PTFE) can be added to the bath to give a super-slick finish.

 

Please keep in mind that the tables are general and there are many variations in both electrolytic and electroless plating baths. As the above information indicates, electrolytic and electroless nickel are normally not interchangeable. In general, electroless nickel is more expensive than electrolytic nickel to apply on a square foot basis.