Electroless nickel plating provides parts with a microcrystalline to amorphous nickel-phosphorous alloy coating. This coating creates a barrier on the substrate and maximizes the objects surface corrosion resistance. Electroless nickel plating is offered in three different phosphorus content weights: Low Phosphorus, Mid Phosphorus, and High Phosphorus. The phosphorus content can be changed to best fit your needs for corrosion, wear, and hardness.
Electroless nickel is generally applied to a thickness range of 12 to 25 microns (0.0005” to 0.001”) and typically does not require further surface finishing, machining, or grinding after plating. The coating creates a thick barrier that fills any minor imperfections in the substrate. Due to its uniformity, electroless plating is superior to its electrolytic counterpart. The hardness and wear resistant properties also stand out against other surface finishes.
After the electroless nickel plating process, parts can be heat treated at relatively low temperatures (400° C to 450°C) to achieve higher hardness (up to 1000 HVN); however, corrosion resistance is reduced.
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The electroless nickel plating process involves depositing a uniform layer of nickel-phosphorus alloy onto the surface of an object. Each step of the plating process is critical in creating a high quality surface finish. Depending on the substrate being plated, the following process specifics may vary.
The electroless plating process starts with an inspection of the parts to verify the overall quality, condition and record the pre-plate dimensions. Parts are then degreased to remove any remaining oil from storage, shipping, or machining. In some cases, after being degreased, parts will be heat treated for stress relief to remove or reduce the internal stresses that were created in the metal during the manufacturing process. In preparation for the chemical pretreatment, parts are masked off; exposing only the surfaces that are to be plated with the electroless nickel.
Once masking is completed, the parts will soak in a chemical bath to activate the pores of the substrate in order to achieve better adhesion with the electroless nickel plating. A thorough rinse with water after the chemical pretreat is the most important part of the process. This will remove any remaining chemical, dirt, or debris that may otherwise get trapped under the coating or ruin the electroless nickel chemistry. Parts are then submerged into the plating bath.
The autocatalytic reaction between the nickel and the reducing agent in the bath deposits nickel onto the metal substrate without the use of anodes or an electrical current, hence the name “electroless”. Since no high or low current densities exist, a very uniform thickness can be achieved, even over irregular shapes.
Once the electroless nickel plating is finished, the parts are rinsed again to remove any excess plating chemicals. This will also safeguard the parts from staining. If necessary, parts will receive a hydrogen embrittlement bake to harden the nickel and promote adhesion. Lastly, parts receive a final inspection that covers visual, dimensional, and adhesion. U.S. Chrome specializes in this process to provide a quality finish to each and every application.
There are three common types of electroless nickel: Low Phosphorous, Mid Phosphorous, and High Phosphorous. These finishes are distinguished by the percentage of weight phosphorus in the electrolyte bath, and each offers different functional properties, such as high corrosion resistance, high wear resistance, solderability and hardness. The electroless plating process is closely monitored and controlled to ensure that the desired composition is achieved, and the intended properties are exhibited in the surface finish.
Low Phosphorus Electroless Nickel
Low Phosphorus coatings are plated in a bath that contains between 1% to 4% Phosphorus content. Parts using this coating exhibit increased hardness (58-62 HRc), reduced wear, higher temperature resistance, increased electrical conductivity, and better solderability. Corrosion resistance is good when used in high pH (alkaline) environments, but poor in acidic environments. The low phosphorus electroless nickel plating can be applied with little or no compressive stress, decreasing fatigue failure.
Mid Phosphorus Electroless Nickel
Mid Phosphorus coatings, which are the most common, are plated in a bath that contains between 5% to 9% phosphorus content. Parts using this coating exhibit increased hardness (45-57 HRc), which can be increased through heat treatment (65-70 HRc) and moderate wear resistance. Corrosion resistance is good when used in both high pH (alkaline) and acidic environments due to a lower porosity from the higher percentage of phosphorus. The phosphorus range that is used when plating will be dependent on the applications needs. For applications that use mid phosphorus electroless nickel plating, the following guideline can be used: 6% to 9% for industrial applications, 5% to 9% for electronics, and 5% to 7% for decorative applications.
High Phosphorus Electroless Nickel
High Phosphorus coatings are plated in a bath that contains between 10% to 12% phosphorus content. Parts using this coating exhibit very high corrosion resistance, increased hardness (45-57 HRc), ductility, and stain resistance. High phosphorus electroless nickel plating is preferred for oil drilling and coal mining parts that will be exposed to highly corrosive acidic environments. The coatings corrosion protection characteristics come from its amorphous finish that is void of any crystalline structures.
Be sure to choose the appropriate electroless nickel coating needed for the corrosive environment it will be used in. While the phosphorus count isn’t the only factor in maximizing electroless nickel corrosion resistance, it is the most important one. Other factors include a proper pre-plating and post-plating process, effective pre-treat process, quality bath chemicals, monitoring for impurities, and exact coating thickness.
Corrosion is one of the major problems challenging today’s industrial engineers. The effects of corrosion can range from diminished appearance to increased operating costs. Previous solutions for corrosion involved metallic coatings, such as chromium, that are inherently porous or feature micro cracking. These solutions did offer some protection to the base metal but would still fail in a short period of time.
The use of electroless nickel eliminates these issues to offer better corrosion protection. The coating’s inherent low porosity to amorphous finish create a true barrier around the component to protect it from substances that would otherwise easily corrode it. Nickel also has excellent resistance to most liquids and atmospheric conditions. Compared to coatings that were prominently used in the past to solve this issue, parts that are plated with electroless nickel and then subjected to highly corrosive environments will last more than ten times longer.
Important factors that determine how effective electroless nickel plating will be in corrosive environments:
Electroless nickel is generally applied to a thickness range of 12 to 25 microns or 0.0005” to 0.001”. After the barrier coating has been applied, it typically does not require any further surface finishing, machining, or grinding after plating. We can plate to the thickness required on your print or have a conversation about the part, its requirements, the environment it will be in, and how it will interact with other metal surfaces to offer the best thickness deposit.
There are many advantages to using electroless nickel on parts and components. The main advantage is the coatings corrosion protection qualities. For instance, electroless nickel is able to withstand 48-100 hours of direct salt spray exposure (ASTM B117) before any signs of red rust become apparent.
No matter the geometry of the part being plated, nickel will be deposited uniformly. This uniformity is achievable due to the lack of current density distribution that is inherent in electrolytic processes. Electrolytic processes may be nonuniform for many reasons, for example, if an objects surface has varying depressions, those spots, that are farther away from the anode, will not receive as much plating material. The absence of electricity in the process also removed the costs that would normally be associated. Cost is further reduced by the need for fewer coats than electroplating.
Manufacturers partner with U.S. Chrome Corporation for their electroless nickel plating needs. These OEMs come to us for our industrial plating knowledge and expertise. They know our proprietary electroless nickel plating solutions will give them the best quality product.
We plate to many different electroless nickel specifications including, but not limited to:
See more of our specifications and certifications.
Electroless nickel plating can be applied to a wide variety of metals and the most common that we work with are aluminum and steel. Other materials that can be plated include, but are not limited to, stainless steel, bronze, copper, titanium, Inconel, Invar, brass, and plastic (although plastic is the only material that U.S. Chromes does not plate). Being that electroless nickel plating to parts and components made out of aluminum alloys is so uncommon, U.S. Chrome created a proprietary plating method to ensure the highest quality adhesion and coating finish. If you have aluminum parts that need this surface finish, please contact our surface engineering team.
There are many applications that benefit from the corrosion protection, wear resistance, coating uniformity and hardness provided by electroless plating. Typical applications that use electroless nickel include bearings, rollers, hydraulics, heat exchanges, valves, rotors, impellers, shafts, gears, kitchen utensils, fixtures, and conveyors. An important aspect of the coating is the uniformity.
On applications that have threads, the uniformity of the coating and precision of the plating process maintains the integrity of the threads. Oil and gas production is an important industry for electroless nickel plating as well. Applications are typically found in corrosive environments where electroless nickel exceeds, such as deep sea rigs. Aerospace engineers frequently combine the corrosion protection, wear resistance, hardness, and solderability of electroless nickel with the density and light weight of aluminum. No matter the application or industry, electroless nickel will provide the needed characteristics and versatility for extended life in the field.
U.S. Chrome offers electroless nickel at our Illinois, Ohio, and Connecticut locations. Each facility is strategically located for fast and efficient delivery to anywhere in America and across the globe. If you are looking for an alternative to electroless nickel, please visit our sister company, USC Technologies.
We’re confident US Chrome will be your best option for your electroless nickel plating applications because of our engineering approach, exceptional customer service, and regional locations. Contact us with your questions or coating challenges.
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