Ensuring the coating performs adequately in service involves careful consideration of its specification prior to it being processed in a plating bath.
Specifying the Wrong Phosphorus Content
Low, medium and high-phosphorus grades of Electroless Nickel Plating are available. Low-phos EN coatings are very hard and therefore suitable for wear resistance applications. High-phos coatings have superior corrosion resistance but start off soft. Therefore it is extremely important to select the correct grade of coating for the specific application.
Skimping on Surface Preparation
Unsatisfactory adhesion to the substrate of an electroless nickel plated part, which cannot be repaired, is usually a preparation error. Contamination, oxide layers, inadequate etching as well as previous coating(s) of the part in question must be fully described to the plating shop and the required pre-treatment stipulated.
Ignoring Dimensional Allowance
As the coating builds up to a specified thickness, it will add thickness to every surface on the part, including inside holes and flat surfaces that will be in contact with other parts. Therefore, a dimensional allowance needs to be included in the design of the part before it is plated.
Missing Post-Plate Heat Treatment
Although the Electroless Nickel Plating can be hardened after application, it is a pre-requisite to undertake a Hydrogen Embrittlement Relief treatment after plating, especially if high strength steel parts have been coated. This treatment will raise the hardness of the coating and most importantly relieve any hydrogen embrittlement that may have occurred during the coating process.
Not Checking Bath Control Practices
The amount of consistent deposits that are created depends on the tight bath chemistry monitoring that is required. It is wise to ask a supplier for the frequency with which they analyse the bath chemistry, as well as the process controls that are in place. For Electroless Nickel Plating, see www.poeton.co.uk/surface-treatments/plating/electroless-nickel-plating/.
Committing Without Reviewing Alternatives
Although electroless nickel is a very versatile coating there are instances where a harder wearing surface (e.g. hard chrome) or a corrosion resistant coating (e.g. zinc nickel or conversion coating) would be more cost effective and still meet the required wear or corrosion resistance. Taking 10 minutes to review alternative coatings before committing to a particular coating could save hours of redesign time later.
Getting the coating right from the start is so much cheaper than repairing a failure later on.
