Advantages of Duplex Electroless Nickel Coatings

Electroplating has been a popular and effective coating process for many years. As with any industrial coating process, electroplating has made significant advances over the past three decades. Today, plating options like electroless nickel plating give professional coaters the ability to tailor coatings to specific applications. In this guide, we will present some of the many advantages of an electroless nickel (EN) plating process called double-layer or “duplex” EN coating.

Electroless Nickel Plating vs. Duplex Plating

Electroless nickel plating is the process by which a metal substrate is coated with a thin layer of a nickel alloy using chemical baths and catalytic processes to achieve the desired coating. Unlike traditional electroplating finishes, no electrical current is passed through the chemical baths; instead, complex chemistry is essential in coating the substrate with an appropriate nickel alloy layer, such as nickel-boron or nickel-phosphorus.

Duplex EN coating takes the electroless process and adds a subsequent step. Typically, the duplex process combines two types of EN deposit layers to achieve a superior finish that better resists corrosion and wear. The process itself is the same – it is only the combination of two nickel alloy layers that truly differentiates duplex from single-layer EN plating.

Why Choose Duplex Plating?

Industrial metal finishers may select from numerous options when it comes to plating substrate metals. While single-layer electroless nickel finishes have their applications across industries, there are times when this type of coating simply is not sufficient. Duplex EN coatings build on the success of single-layer finishes, offering advantages like:

  • More reflective deposit layers
  • Improved wear resistance
  • Superior corrosion resistance
  • Improved surface lubricity
  • Better surface release properties

Examples of Duplex EN Finishes: Achieving Superior Results

Advances in chemical science have unlocked new techniques for industrial finishing companies, giving them the ability to coat substrate metals for specific applications. These applications may be in harsh environments, necessitating a more durable and corrosion resistant finish than is possible with single-layer EN plating. Duplex plating performs by blending two different layers, usually with different chemical properties and levels of phosphorus ions in the chemical baths. Some examples of duplex plating include:

High phosphorus over low phosphorus – low phosphorus EN provides hardness and wear resistance, but it is not great at providing corrosion protection. By adding a layer of high phosphorus EN over the first layer, corrosion resistance is improved dramatically.

Bright mid-phosphorus over high phosphorus – in some applications, a bright decorative plated finish is desired. By coating a high phosphorus EN layer with a bright mid-phosphorus layer, great corrosion resistance and an attractive finish are achieved.

Composite over high phosphorus – when a particular substrate finish needs to have lubricity/release properties and also great corrosion resistance, a single-layer of high phosphorus EN may not be enough to achieve the desired results. To overcome this, coaters can start with a high phosphorus EN layer and coat it with a composite layer, typically a plating layer that contains polytetrafluoroethylene (PTFE) or boron-nickel (BN) alloy.

There are many other options when it comes to duplex electroless nickel plating processes. Professional coating service providers have the tools, the techniques, and the experience to achieve finishes that meet specific needs of end users, regardless of industrial application.