Nickel is a hard and self passivating metal. Those qualities make it an ideal constituent of alloys like stainless steel and German silver, and as a surface treatment (often in combination with phosphorous or PTFE). However, the method by which the coating is applied can make a significant difference to the result.
Application methods fall broadly into two approaches – electroplating and electroless methods that use an autocatalytic reaction to deposit the layer of nickel or nickel composites.
Electroless nickel plating is often the best method when the main objective is corrosion protection. Typically, the immersion solution contains a fluid alloy of nickel and 4-14% phosphorous, along with reducing agents. This is maintained at a temperature around 90 degrees centigrade to encourage the reaction to take place.
The result is a very even layer that penetrates into every corner equally. The finished surface appearance is very similar to an electroplated one.
When the percentage of phosphorous is low the finished product has better high temperature tolerance and greater density, but a high phosphorous content gives even higher corrosion protection and a more glass-like finish.
By contrast, the deposition layer produced by electroplating is about 99% nickel. It still provides corrosion protection but not as much as the electroless methods can.
Electroless methods create the opportunity to deposit nickel composites. These are usually combinations of nickel and a polymer such as PTFE. When well dispersed the PTFE imparts a low friction and non-stick surface without impairing the hardness or corrosion resistance of the nickel or nickel/phosphorous alloy. These surfaces are substantially more wear-resistant than one created by nickel electroplating.
Nickel can also form useful composites with graphene. The result is an extra hard surface with increased thermal conductivity.
Generally speaking, electroplating produces a shinier more appealing surface than electroless deposition. On the other hand, it can be used to deliberately create a light-resistant dark surface.
For some products, the ideal surface treatment strategy may involve more than one type of treatment – either consecutively or on different parts of the item. This might be a simple heat application in some cases but can be more complex in others. In practice there are many proprietary, or bespoke, treatment refinements available and we always recommend contacting a specialist early in your design process.