There are two methods of depositing a thin layer of nickel onto the surface of a metallic object. One is electroplating, the other electroless plating. So what is the difference and why would you use one over the other?
In this post we’ll look at the differences between these two types of nickel plating, from the chemistry behind the processes, to the ideal uses for each.
The process of electroplating occurs when a rod of the plating method is used as an anode. The anode is immersed in a bath of electrolyte which contains the salt of the metal to be plated. For nickel plating, the salt used is Nickel Chloride.
With electroplating, two or three plating processes may be used, sometimes with a layer of a different metal underneath to improve adhesion.
Disadvantages of electroplating
Electroplating may result in hydrogen embrittlement, where the hydrogen gas leaks out at the surface of the cathode and diffuses into the surface of the component to be plated, making it brittle.
This embrittlement can be reduced by post plate heat treatment at a low temperature, which reverses the process of hydrogen diffusion into the surface layers of the component.
Electroless nickel plating
The other method of plating with nickel is electroless nickel plating. This type of plating doesn’t need an electric current because it happens using a chemical reaction.
The electroless nickel solution consists of nickel ions, reducing agents and other chemicals. The most commonly used reducing agent is sodium hypophosphite.
Electroless nickel plating has many fantastic properties which makes the process superior to other types of metal plating.
- The process extends the life of any component that it coats.
- The metal layer deposited by the electroless nickel plating process has an even thickness over all surfaces of the component.
- This effect cannot be achieved with electrodeposited coatings.
- Electroless nickel plating also provides excellent wear and corrosion resistance, as well as hardness and lubricity.
Another advantage of the process of electroless nickel plating is that the parts to be plated do not need to conduct electricity. This means that electroless nickel plating can be applied to ceramics, composites and polymers.
This method of plating is great for producing prototypes of metallic parts by plating a polymer casting or part to give some idea of the finished piece.
It is still possible for electroless nickel plated parts to suffer from hydrogen embrittlement, so for parts that are prone to corrosion through use, post heat treatment may be needed to improve the adhesion of the nickel and reduce the internal stresses within the nickel that has been deposited. When heat treating electroless nickel, it is also important to ensure that the heat treatment doesn’t temper-soften the existing material.
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