Electroless plating properties
Coatable Alloys and Adhesion
The electroless nickel plating treatments in the NIPLATE® family can be applied to most of the metal alloys used in precision engineering. One of the main strengths of this process is the excellent adhesion of the coating to the base material, achieved thanks to the chemical bond that forms between the deposited nickel-phosphorus alloy and the properly prepared metal substrate.
However, adhesion is not an “automatic” property: it depends directly on the base material, its metallurgical condition, and the surface condition of the part as received for processing.
The role of surface preparation
The electroless nickel plating process includes a controlled sequence of chemical pre-treatments designed to remove contaminants, oxides and surface films, activating the surface before deposition of the NIPLATE® coating.
This phase is essential to ensure:
- correct initiation of the autocatalytic reaction;
- continuity of the deposited layer;
- high resistance to coating detachment during service.
In many cases, chemical pre-treatments are sufficient. However, some alloys or metallurgical conditions require additional mechanical pre-treatments.
Critical alloys and mechanical pre-treatments
Some materials naturally have surfaces that are more difficult to activate chemically. This is particularly the case for:
- stainless steels, due to the presence of a stable passive layer;
- steels subjected to thermochemical treatments such as case hardening, which may have chemically altered or oxidized surfaces;
- titanium alloys, characterized by passive surface oxides.
For these alloys, a mechanical micro-sandblasting pre-treatment is generally required, with the purpose of removing the passive or altered surface layer and promoting the initial anchoring of the coating.
Micro-sandblasting increases surface roughness, typically in the range of Ra 1.00 to 1.60 µm; this value must be assessed based on the functional requirements of the component.
Heat treatments and adhesion
In the case of stainless steels and thermochemically treated steels, coating adhesion can be further improved by a subsequent heat treatment after electroless nickel plating, carried out at temperatures equal to or higher than 250 °C.
This treatment helps stabilize the interface between the coating and the base material, increasing adhesion.
Coatable alloys and recommended pre-treatments
The following table provides an indicative summary of the main base materials and whether mechanical pre-treatments are required before electroless nickel plating:
| Alloy | Mechanical pre-treatment |
|---|---|
| Carbon steel | No mechanical pre-treatment required |
| Case-hardened steel | Sandblasting required |
| Stainless steel | Sandblasting required |
| Aluminum alloys | No mechanical pre-treatment required |
| Copper alloys | No mechanical pre-treatment required |
| Titanium alloys | Sandblasting required |
These indications should be considered general guidelines: the material condition, machining operations and final application may require specific assessments.
PRACTICAL RECOMMENDATIONS
- Always clearly identify the base material to be coated in the drawing.
- The material must have no residual magnetism, which can create defects of excessive roughness.
- Parts must be clean or protected with oils that are readily soluble in water-based detergents.
- There must be no surface contaminants that cannot be removed by standard pre-treatments (heavy oils, polishing compounds, adhesive residues, marker marks, etc.).
- The surface must be free of defects such as cracks, porosity, burrs, deep oxidation, inclusions or welding slag, which can compromise adhesion and coating quality.
In summary, proper adhesion of the electroless nickel plating coating is the result of a controlled combination of base material, surface preparation and process. Careful evaluation of these factors is essential to achieve reliable and repeatable performance over time.