Similar to burnishing and chrome plating, chemical nickel plating is one of those surface treatments that give metal components new properties. In this article, therefore, we delve into what electroless nickel plating is and what advantages it brings.
What is Chemical Nickel Plating?
Chemical nickel plating is a surface treatment of a metal alloy, which is carried out by immersion in a nickel sulphate solution. To this is added a chemical reductant, usually represented by sodium hypophosphite, capable of generating a controlled autocatalytic reaction.
The oxidation-reduction that takes place between the nickel sulphate cation and the sodium hypophosphite anion gives rise to a nickel-phosphorus deposit, which will coat the surface of the treated part.
The coating takes place chemically and no electric current is involved: the result is a nickel layer of uniform thickness, suitable for both threaded elements and internal surfaces.
As far as the materials that can undergo the treatment are concerned, there are no particular restrictions: almost all alloys used by precision mechanical shops can undergo this process.
The Advantages of Electroless Nickel Plating
The advantages of using chemical nickel plating are manifold and mainly affect the strength of the treated part.
Thanks to this nickel-phosphorus layer, the part acquires anti-corrosion and wear protection. In addition, the combination with further heat treatment allows a very high degree of hardness to be achieved.
Aesthetically, the treated parts take on a very bright metallic colour, which remains for some time before oxidising. Their morphological characteristics remain unchanged, with a slight increase in thickness given by the coating.
Thickness of Chemical Nickel Plating
As mentioned, one of the advantages of this technique is the uniform distribution of the nickel-phosphorus layer, regardless of the shape of the part. The thickness of the coating, however, must be carefully studied, based on certain parameters.
First of all, the desired degree of resistance must be considered. Also decisive are the environmental conditions to which it will be subjected, the concentration of phosphorus in the electroless nickel, and the type of material to be exposed to the treatment.
The characteristics of the part, such as porosity, and the reactions that can be triggered between the base and the coating determine the greater or lesser durability of the nickel plating.
As a result, the thickness can vary significantly, ranging from 5 to 50-100 microns. This is the case, for example, with components designed for the marine environment, which are continuously stressed and exposed to corrosive action.
As the microns increase, so does the resistance, which is why the height of the coating must be carefully evaluated and chosen.
Chemical or Electrolytic Nickel Plating?
Electrolytic nickel plating, or electroplating, is very different from its chemical counterpart, both in execution and in areas of use.
Firstly, this treatment uses electric current to deposit the coating on the component. Such a method results in a layer with an uneven thickness, higher at the edges and almost absent on the inner surfaces.
It is not suitable for technical areas and is therefore often used as a decorative coating.