Electroless Nickel Plating

Electroless nickel plating is used in applications where corrosion resistance is desirable and when plating intricate surfaces or small or deep bores, for a uniform thickness and medium to high hardness. The process is limited to certain types of metals and it requires a strict, high level of quality control.

Electroless nickel plating is an auto-catalytic reaction used to deposit a coating of nickel on a substrate. Unlike electroplating, it is not necessary to pass an electric current through the solution to form a deposit. This plating technique is to prevent corrosion and wear. EN techniques can also be used to manufacture composite coatings by suspending powder in the bath. Electroless nickel plating has several advantages versus electroplating. Free from flux-density and power supply issues, it provides an even deposit regardless of workpiece geometry, and with the proper pre-plate catalyst, can deposit on non-conductive surfaces.

Electroless coating (also known as autocatalytic coating) is defined as the deposition of a metallic coating by a controlled chemical reduction that is catalyzed by the metal or alloy being deposited.

By far the most common form of electroless coating is nickel plating, which is actually a nickel-phosphorus alloy (2-10% P). Electroless nickel has the unusual quality of being amorphous and not crystalline in structure. These coatings possess high hardness, natural lubricity, and good wear and abrasion resistance.

Electroless nickel plating (EN) is an auto-catalytic chemical technique used to deposit a layer of nickel-phosphorus or nickel-boron alloy on a solid workpiece, such as metal or plastic. The process relies on the presence of a reducing agent, for example hydrated sodium hypophosphite (NaPO2H2•H2O) which reacts with the metal ions to deposit metal. The alloys with different percentage of phosphorus, ranging from 2-5 (low phosphorus) to up to 11-14 (high phosphorus) are possible. The metallurgical properties of alloys depend on the percentage of phosphorus.

Electroless nickel is sometimes an economical treatment to improve the performance of carbon steel in mildly corrosive environments (such as chlorides, trace acids, caustic solutions) and in situations where light wear may occur in service. It is, however, difficult to deposit electroless nickel on chromium-containing steels. Electroless nickel can be deposited on the internal diameter of tubular components and other difficult to access surfaces.

There are variants of electroless nickel plating, the most common of which include:

• composite electroless nickel, in which SiC (silicon carbide) particles are co-deposited with the nickel to enhance its strength and wear resistance
• duplex electroless nickel where an undercoat containing 14% phosphorus is used with a top coat of 5% phosphorus.