Electroless nickel (EN) plating is a chemical reduction process which depends upon the catalytic reduction process of nickel ions in an aqueous solution (containing a chemical reducing agent) and the subsequent deposition of nickel metal without the use of electrical energy. Due to its exceptional corrosion resistance and high hardness, the process finds wide application on items such as valves, pump parts etc., to enhance the life of components exposed to severe conditions of service, particularly in the oil field, marine sector, pharmaceuticals plant.
In the EN plating process, the driving force for the reduction of nickel metal ions and their deposition is supplied by a chemical reducing agent in solution. This driving potential is essentially constant at all points of the surface of the component, provided the agitation is sufficient
to ensure a uniform concentration of metal ions and reducing agents. Electroless deposits are therefore very uniform in thickness all over the part's shape and size. This process offers distinct advantages when plating irregularly shaped objects, holes, recesses, internal surface, valves or threaded parts.
Advantages of EN plating
- Uniformity of the deposits, even on complex shapes.
- Deposits are often less porous and this provides better corrosion protection to steel substrates,
much superior to that of electroplated nickel and hard chrome.
- The deposits cause about 1/5th as much hydrogen absorption as electrolytic nickel and about 1/10th as much hard chrome.
- Deposits can be plated with zero or compressive stress.
- Deposits have inherent lubricity and non-galling characteristics, unlike electrolytic nickel.
- Deposits have good wetability for oils
- Generally low phosphorus and especially eletroless nickel boron are considered solderable.
- Mid and high phosphorus EN's are far worse for solderability
- Deposits are much harder with as-plated microhardness of 450 - 600 VPN which can be increased to 1000 - 1100 VHN by a suitable heat-treatment