Electroless Nickel Plating Finish Options Explained

Electroless Nickel Plating Finish Options Explained

The key factor which determines the properties of an electroless nickel coating is the phosphorus content. An incorrectly specified coating can fail to meet the requirements of the application for which it is intended.

Low Phosphorus Deposits

A low phosphorus coating is one of the hardest types of coatings available, with an average hardness of approximately 850 HV when deposited. These types of coatings are best for components that will be subjected to abrasion immediately after plating. While they do exhibit moderate corrosion resistance, the appearance of the coating is typically slightly brighter than medium or high phosphorus coated components.

Medium Phosphorus Deposits

The medium phosphorus type (5% – 9% P) is one of the most popular types. Medium phosphorus Nickel coatings have reasonable hardness and good corrosion protection, and thus can be used for general engineering components, such as hydraulic parts, pumps, etc. They produce a semi-bright appearance, and have good dimensional accuracy.

High Phosphorus Deposits

High phosphorus coatings (10-13% P) provide the highest level of corrosion resistance and are ideal for extremely aggressive chemical services or for services exposed to salt spray testing. High phosphorus deposits are virtually amorphous and have a low number of grain boundaries which are the primary paths of corrosion. These coatings have a lower hardness than the other two types and may benefit from post plating heat treatment.

Matching the Finish to Your Part

Wear is the dominant specification criterion for low phosphorus (LP) coating. In all other cases, the dominant specification criterion is corrosion. Thus for general engineering parts, including hydraulic components, pumps, and engineering moulds, medium phosphorus (MP) coating is the normal specification. Many organisations that specify engineering materials, including hydraulic components and engineering parts, use the material selection guidance from an institution such as the Institution of Mechanical Engineers to form a formally documented specification for the part.

Getting the amount of phosphorus in the coating right the first time can save a lot of money in stripping and re-plating later.