Q&A: Nickel Phosphorous Plating

Q. Can you give me any information about nickel phosphorous electrolytic plating? Does it have the same set of properties as electroless nickel plating? H.S.

A. Electrolytic nickel phosphorous plating is not widely used in the United States. However, it does offer some unique properties not found in other plating processes. Typically, nickel phosphorous alloys are plated using an electroless process. The electroless process will give you a very uniform deposit, but thicknesses are usually limited by the plating bath, and you need to continuously monitor and add additional materials to the bath. The electrolytic nickel phosphorous plating bath allows for thicker deposits, and the newer formulations do not require the attentiveness of the operators that the electroless process requires.

The electrolytic nickel phosphorous plating bath is based on a patented process developed by NASA and the University of Alabama. Some of the advantages of this plating process compared to electroless nickel phosphorous plating are given below:

1. Metal additions are not necessary because the anodes provide the nickel.
2. A consistent plating rate can be maintained throughout the plating process.
3. Plating tanks do not have to be stripped as in electroless plating.
4. Deposits of varying thickness can be obtained.
5. Corrosion-resistant alloys similar to those obtained with electroless nickel are available.
6. Much less operator interaction is required compared to electroless nickel.

A comparison among some of the properties of electrodeposited nickel phosphorous and other materials is shown in the table below:

Parameter	Electrodeposited Ni	Electroless Ni	Electrolytic NiP
Plating Temperature	38 – 50°C	82 – 90°C	45 – 60°C
Metal Concentration Control	Soluble anode	Chemical additions	Soluble anode
Ultimate tensile strength	800 MPa	850 MPa	1,800-2,150 MPa
Hardness (Rockwell C)	22-24	48 – 52	55 - 64
Thick Deposits	Yes	No	Yes