The process of depositing a nickel layer onto a metal or certain non-metallic substrate using electrolysis or a chemical method is called nickel plating. Nickel plating is divided into two main types: Electroplated nickel and electroless nickel plating.
Electroplated nickel involves an electrolytic bath consisting of a nickel salt, conductive salts, a pH buffer, and a wetting agent. The anode is metallic nickel, and the cathode is the workpiece to be plated. When a direct current is applied, a uniform and dense nickel deposit is formed on the cathode. Nickel deposited from a bath containing brighteners is known as bright nickel, while nickel deposited from a bath without brighteners is referred to as dull nickel.
Electroless nickel plating is a process in which nickel ions in an aqueous solution are reduced by a reducing agent under specific conditions, leading to the deposition of nickel onto the solid substrate surface.
Characteristics of Electroplated Nickel
High Stability in Air: The electroplated nickel layer exhibits high stability in the atmosphere. Due to nickel’s strong tendency to passivate, a very thin passive film rapidly forms on the surface, which resists corrosion from the atmosphere, alkalis, and certain acids.
Excellent Polishability and Finish: Electroplated nickel deposits have a fine crystalline structure and excellent polishing properties. A polished nickel coating can achieve a mirror-like finish, which retains its luster for a long time in the atmosphere. Consequently, nickel plating is frequently used for decorative purposes.
High Hardness and Wear Resistance: The hardness of a nickel coating is relatively high, which can improve the surface wear resistance of the final product. Nickel plating is often used in the printing industry, for example, to enhance the hardness of lead surfaces.
Broad Range of Applications: Nickel plating is widely used as a protective and decorative coating on the surfaces of steel, zinc die-castings, aluminum alloys, and copper alloys to protect the base material from corrosion or to provide a bright, decorative finish. It is also often used as an intermediate layer for other platings, such as a thin layer of chromium or a simulated gold layer, to provide better corrosion resistance and a more attractive appearance.
High Production Volume: Due to its many excellent properties, electroplated nickel accounts for the second-largest volume in the plating industry, second only to zinc plating, with consumption representing approximately 10% of the total nickel output.
Characteristics of Electroless Nickel Plating
Uniform Thickness: A major advantage of electroless nickel plating, and a key reason for its widespread use, is its excellent uniformity and throwing power. Electroless nickel avoids the non-uniform thickness issues that can arise in electroplating due to uneven current distribution. As long as the part surface is in contact with the plating solution, and the consumed chemical components are replenished promptly, the deposit thickness is virtually the same across all areas of the workpiece, even in recesses, crevices, and blind holes.
No Hydrogen Embrittlement: The plating process does not introduce hydrogen into the workpiece, meaning there is no risk of hydrogen embrittlement, and post-plating hydrogen relief treatment is unnecessary.
Superior Functional Properties: Many functional properties, such as corrosion resistance and high-temperature oxidation resistance, are often better than those of electroplated nickel.
Applicable to Various Substrates: Electroless nickel plating can be deposited on the surfaces of various materials, including steel, nickel-based alloys, zinc-based alloys, aluminum alloys, glass, ceramics, plastics, and semiconductors. This versatility creates opportunities for enhancing the performance of these materials.
No External Power Source Required: Electroless nickel plating does not require the direct current generators or control equipment typically needed for electroplating.
Low Heat Treatment Temperature: By applying heat treatment below 400 °C for different durations, varying degrees of corrosion and wear resistance can be
achieved. This makes EN plating particularly suitable for functional coatings on complex parts that require wear and corrosion resistance.
Electroless Nickel Plating Process
Cleaning: The surface to be plated must be meticulously cleaned to remove any dirt, oil, or other contaminants that could compromise the adhesion of the electroless nickel layer. Various chemicals are used to remove grease, fingerprints, cutting fluids, and other materials left over from manufacturing.
Activation/Catalysis: The part surface is activated, often by immersion in an acidic solution, to remove any oxide layer. This step is critical for ensuring reliable adhesion of the electroless nickel coating.
Pre-treatment: Depending on the base material (substrate), a pre-treatment may be necessary to enhance the adhesion and corrosion resistance of the nickel layer. Pre-treatment processes may involve applying a zincate solution or a palladium catalyst to the surfaces that will be plated.
Electroless Nickel Plating: The part to be plated is immersed in a solution containing nickel ions, a reducing agent, and other necessary electroless nickel chemicals. The reducing agent chemically converts the nickel ions into metallic nickel, which deposits onto the part’s surface.
Post-treatment: After electroless nickel plating, depending on industry requirements, parts may be rinsed, dried, and subjected to post-treatments to further improve adhesion, corrosion resistance, and other performance characteristics.
Applications of Electroplated Nickel
Repair and Restoration: Nickel plating is widely applied in functional areas, such as restoring worn or corroded parts, often through localized plating using brush plating technology. It is also used in electroforming processes to manufacture electroformed molds for the printing industry, record stampers, and other types of dies.
Wear-Resistant and Self-Lubricating Coatings: Thick nickel deposits offer good wear resistance and can be used as a wear-resistant coating. Notably, the recent development of composite electroplating allows for the deposition of a composite nickel layer embedded with hard, wear-resistant micro-particles, resulting in even higher hardness and wear resistance than pure nickel plating. When graphite or fluorinated graphite is used as the dispersed particle, the resulting nickel-graphite or nickel-fluorinated graphite composite coating exhibits excellent self-lubricating properties and can be used as a lubricating coating. Black nickel plating is also extensively used for optical instruments or as a decorative finish.
Protective, Decorative, and Intermediate Layers: As mentioned, nickel plating serves as a protective and decorative coating on materials like steel, aluminum alloys, and copper alloys. It protects the base material from corrosion and provides a bright, decorative effect. It also frequently serves as an intermediate layer onto which a thin layer of chromium or a simulated gold layer is subsequently plated, which improves corrosion resistance and aesthetic appeal. For functional applications in specialized industries, nickel layers of approximately 1 to 3mm thickness are deposited on parts for repair and restoration. Its applications are increasingly vital in manufacturing continuous casting molds, dies for electronic component surfaces, molds for alloy die-casting, complex aerospace engine components, and micro-electronic elements.
Recommendation
When implementing nickel plating for your components, it’s essential to consider the specific requirements of your application, including the need for uniformity, corrosion resistance, hardness, and whether the process must be autocatalytic (electroless) or electrolytic (electroplating).
At Getzshape, we specialize in manufacturing services and advanced surface finishing technologies, including both electroless and electroplated nickel solutions. To explore how nickel plating can enhance your next project, please visit our website at www.getzshape.com, or send your engineering specifications directly to us.
