Most raw materials apart from precious metals will easily oxidize and corrode over the course of time if they get exposed to several environmental situations or corrosive applications. Many components need to be designed with a surface engineering evaluation that will ensure that the final product can function safely and effectively over its intended lifespan. Even the smallest evidence of corrosion can easily cause serious shortfalls on the functionality of some parts and components. Electroless nickel plating provides the ultimate solution that prevents corrosive attacks over a number of corrosive mechanisms such as chemical attack corrosion or galvanic corrosion.
Electroless nickel plating is applicable to a number of basic metals such as brass, copper, steel, and different aluminum alloys; it is currently used for the promotion of corrosion performance over a diverse range of industries but especially power transmission, oil and gas, heavy equipment, marine, automotive and railway among others. Electroless nickel plating doesn’t require an external source of electrons for deposition; it uses an auto catalytic process that doesn’t require that passage of an electric current through the parts in order to form that plated deposit that gives improved uniformity over the electrolytic deposit. It is this uniformity in electroless nickel plating that that improves corrosion resistance in all features of the part and especially those that were traditionally difficult to coat such as counter bores or through holes.
The other advantage of electroless nickel plating has to do with the fact that nickel will automatically co-deposit phosphorous in varying amounts between 4 and 13 percent depending on the bath type. The level of phosphorous deposition has a direct impact on the deposit properties such as ductility, hardness, and corrosion resistance. Additionally, some post-plate heat treatment is sometimes used in order to change the structure of the electroless nickel plating which will automatically increase hardness to as high as 70 Rc. The traditional electroless nickel plating can be broken down into three different specific groups depending on the amount of phosphorous co-deposition.
High phosphorus: High phosphorous electroless nickel plating provides the greatest level of corrosion resistance thanks to its 11 to 13 percent phosphorus levels; it is also non-magnetic and has the lowest melting point in addition to being the most ductile. The deposit will have a semi-bright appearance and it also has a slower rate of plating as compared to the medium phosphorous electroless nickel plating.
Medium Phosphorus: Medium phosphorous electroless nickel plating has separately been referred to as the workhorse with its 6 to 10 percent phosphorous deposit. It has a good level of corrosion resistance, solderability, and a very high melting point. It has a semi-bright to a bright appearance with its best advantage being that it plates faster thereby reducing the cost.
Low Phosphorus: With less than 5 percent phosphorus deposition, the low phosphorous electroless nickel plating offers the highest hardness but it is the least ductile owing to its microcrystalline as-plated structure; it also offers the least corrosion resistance of the three types of black electroless nickel plating.
This article is penned by Lora Davis for Sheffield Platers, Inc.