Ferromagnetism

Electroless nickel plating NIPLATE® coatings can exhibit different magnetic properties depending on the composition of the nickel–phosphorus alloy and any post-deposition heat treatments. This aspect must be carefully considered in applications where the magnetic behavior of the coated component is a functional requirement or a design constraint.

Influence of Ni–P alloy composition

The nickel–phosphorus alloy deposited by electroless nickel plating can have an amorphous or microcrystalline structure depending on the percentage of phosphorus in the deposit. The resulting atomic structure is the main factor determining the magnetic behavior of the coating.

In general:

• medium-phosphorus alloys have a predominantly microcrystalline structure;
• high-phosphorus alloys have a predominantly amorphous structure in the as-deposited condition.

This structural difference is directly reflected in the presence or absence of ferromagnetism.

Magnetic behavior of the main NIPLATE® coatings

NIPLATE® 600, characterized by a medium phosphorus content (approximately 7%), has a microcrystalline structure and is ferromagnetic under all conditions, regardless of whether heat treatments are performed after deposition.

NIPLATE® 500, characterized by a high phosphorus content (approximately 11%), has an amorphous structure in the initial state and is non-ferromagnetic in the as-deposited condition. However, following a hardening heat treatment carried out at 250 °C or higher, the alloy structure partially evolves toward a microcrystalline configuration, making the coating ferromagnetic.

Application implications

The magnetic behavior of electroless nickel plating coatings must be considered during the design phase for components intended for:

• electromechanical applications;
• sensors and magnetic devices;
• environments where the absence of magnetic interference is required;
• components exposed to varying magnetic fields.

In these cases, the choice of coating and the definition of post-plating heat treatments cannot be considered independently, but must be evaluated together based on the final magnetic requirement of the component.

A clear specification of the treatment helps prevent unwanted variations in magnetic behavior over the component’s service life and ensures compliance with the required performance.