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What is Electroless Nickel Plating?

Electroless Nickel Plating (ENP) is a chemical process that involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power. The reaction is accomplished when hydrogen is released by a reducing agent (normally sodium hypophosphite), and oxidized thus producing a negative charge on the surface of the part. The charge causes a layer of nickel and phosphorus to form and this continues until the part is removed from the solution. Since the plating process requires no electrical current, the coating produced is very uniform and has a dense amorphous structure that can be applied over various metals and substrates to provide corrosion and wear resistance.

There are many different types of Electroless Nickel (ENP) coatings and processes available to meet a wide range of unique applications. Physical and mechanical properties vary considerably from one ENP process to another depending on the phosphorus content, the formulation of the bath and both the pre-plate and post-plate treatments, yet all the EN coatings offer excellent deposit uniformity and superior corrosion protection.

Features of Electroless Nickel Plating (ENP) Coating

  • Corrosion resistance
  • Precise thickness control
  • Uniformity of deposit
  • Increased hardness
  • Abrasion resistance
  • Inherent lubricity
  • Anti-galling and fretting wear protection
  • Quick release properties
  • Non-magnetic properties
  • Conductivity
  • Solder ability/Weld ability/Braze ability
  • Meets a wide range of performance capabilities

Capabilities

We are one of few suppliers in Western Australia our Electroless Nickel Tank Size is approx 800mm x 800mm x 800mm coating items up to 400kg.

Uniform Coating

Because it is an electroless process, the plating rate and coating thickness are the same on any section of the part exposed to fresh plating solution. Even on the most complex and irregular surfaces, close tolerances can be held without any additional machining or finishing. Unlike electroplating, no complicated positioning of anodes is required. Shafts, rollers, gears, nuts and bolts, bearing journals, servo valves and oil nozzles all benefit from EN plating.

Thickness

Electroless Nickel Plating (ENP) can be accurately and uniformly deposited in a wide range of coating thickness. The majority of commercial applications utilize a thickness between 0.1 - 1.0 mils while holding an overall tolerance of 0.1 mil. Thickness of 1.0 - 3.0 mils are common for corrosive service, while deposit thickness above 3.0 mils are typical of repair and rework. Deposition of heavier coatings requires careful process control to avoid roughness and pitting.

Corrosion Resistance

Electroless Nickel Plating (ENP) is a barrier coating, protecting the substrate by sealing it off from the environment. An amorphous alloy, ENP has no crystal or phase structure and is, therefore, more resistant to attack than equivalent polycrystalline materials. Encapsulation is the principal method of protection and corrosion control of the substrate. The ENP plating solution generally penetrates into small voids and surface imperfections as well as on the surface providing excellent corrosion resistance that, in many environments, is superior to pure nickel or chromium alloys. The better the surface finish prior to coating the better the corrosion resistance. Coating thickness, substrate condition and surface preparation are important factors that determine both coating porosity and the ultimate resistance to corrosive attack.

Hard Finish

Electroless Nickel Plating (ENP) coatings offer outstanding protection against wear and abrasion. Additional heat treatment of the ENP coating causes the alloy to age harden and, under lubricated conditions, produce hardness values and wear resistance levels equal to most commercial hard chromium coatings. For some applications high temperature treatments cannot be tolerated because parts may warp, the strength of the substrate may be reduced or maximum corrosion protection may be effected. For these applications, longer times and lower temperatures are used to obtain the desired hardness.

Wear Resistance

Wear is the mechanical loss of material on a surface. There are many types of wear and nearly 200 specific wear tests, making for a complex evaluation of many applications. Wear can be combined into four categories that define most situations.

  • Fretting Wear
  • Adhesion Wear
  • Abrasion Wear
  • Erosion Wear

Front Range Plating can help you determine the best coating for your particular application.

Brightness

The brightness or reflectivity of Electroless Nickel Plating (ENP) may vary significantly depending upon the specific ENP formulation and the condition of the substrate. The solution that produces a bright deposit on smooth surfaces may provide a much duller deposit on a surface that is rough from machining, sand blasting, etching etc.

Lubricity

The phosphorus in the Electroless Nickel Plating (ENP) coating provides natural lubricity and release properties that can be very useful to the performance and function of a plated component. The coefficient of friction for ENP is 0.6 in non-lubricated conditions and up to 0.13 in lubricated conditions. Heat treatment or the level of phosphorus does not significantly affect the frictional properties of the ENP. EN/PTFE composite coatings (PEN-TUF/EN) greatly enhance the inherent lubricity of ENP. Coefficient of friction values range from 0.17 in a dry condition to 0.07 in a lubricated condition.

Solder Ability / Weld Ability

Electroless Nickel Plating (ENP) alloys are easily soldered with a highly active acid flux. Successful welding to ENP can be correlated to the substrate and type of ENP.

Electroless Nickel Plating - Pre-Treatments

Proper pre-treatment can be as important to the successful application of ENP as the actual deposit. Part design, manufacturing processes and surface contamination must be evaluated before determining the pre-treatment required to produce a quality ENP coating. Front Range Plating will assist in this evaluation process to ensure maximum coating performance.

 

Call AAEP Pty Ltd on 08 9495 4995 or send an email to brad@aaep.com.au to see if we can help you with your Electroless Nickel Plating needs. For a quote you can send drawing and/or photo and/or description (make sure to note dimensions, weight, material and type of plating required etc).

 

Electroless Nickel vs Other Materials

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The right nickel coating can eliminate the need for expensive high-alloy materials in corrosive environments, prolong the life of wear components by factors of four or more, improve release properties of moulds, or improve the appearance of metal components.

Effects of Heat Treatment

Where maximum corrosion resistance is required, hardened coatings should not be used. Heat sensitive substrates may also be adversely affected and, as mentioned above, caution is required if subsequent soldering or bonding operations are required or if the part is cosmetic.

Electroless Nickel Plating

Electroless nickel plating, (as it name implies), is a nickel coating in fact an alloy coating containing approximately 10% phosphorous that is deposited by chemical reduction rather than electrolytically.

The coating has remarkable qualities:-

Excellent corrosion resistance.

Deposit uniformity, regardless of the shape of the item plated. Refer Fig 1 and Fig 2

High hardness, as plated 45 RC.

Heat treatable. Nickel phosphorous is a heat treatable alloy and a hardness figure up to 68 RC can be achieved.

Controllable deposit. Close tolerances can be maintained and the need for post plating grinding is eliminated.

Quality finish. Although classed as an engineering coating the deposit has a pleasing stainless steel appearance and is often used to give a product a quality lift.

Coverage by electroplating is uneven, particularly at corners

Coverage of electroless nickel is evenly distributed over total area regardless of shape

Electroless nickel has found application in a broad range of industries :

General engineering.Petroleum and chemical industries
Packaging / materials handling Food
Automotive Mining
Toolmaking Reclamation of worn parts
Aerospace Military
Electronics Hydraulics / pneumatics

The coating is often used as an alternative to stainless steel for cost and practicality reasons

Summary of electroless nickel features:-

  • Excellent corrosion resistance, dependant upon coating thickness
  • Phosphorous content 9-11%.
  • Melting point 890deg C. (the deposit has poor hot hardness)
  • Adhesion to mild steel 30,000 - 60,000psi
  • Hardness as plated 45 RC
  • Hardness after heat treatment of 1 hour at 400degC 68 RC
  • Good solderability.

The letter c indicates that a chromate treatment is to be applied.

Specifications

There is no Australian standard for electroless nickel, however the process is covered by, US and UK specifications namely AMS 2404 (USA) and DEF Std 03-5 (UK). In an addition to this several manufacturers call up their own specification.

Electroless Nickel Coatings - Pre-Treatments Stress Relief / Hydrogen Embrittlement Relief

During processes such as EN plating, hydrogen can be absorbed into the metal substrate especially if the metal is a high strength steel. This penetration can cause cracking and failure of the metal and is known as hydrogen embrittlement. To prevent hydrogen embrittlement, components are baked to diffuse the absorbed properties of the steel almost completely, helping to ensure against failure. The time required to remove hydrogen from steel depends on the strength of the steel. Longer periods or higher temperatures are needed as the strength of a steel increases.

Heat Treat for Hardness

As plated, ENP is one of the harder coatings available and its hardness may be increased by heat treatment. ENP deposits have a maximum achievable hardness and once that level has been reached any further treatment will lower the hardness factor. Heat-treating is generally done in an air-circulating oven, but nickel oxides may form during this process causing undesirable cosmetics or interference with subsequent soldering and bonding operations.