Low-phosphorus electroless nickel plating (ENP 23)

Hardness and wear
resistance for
mechanical components

Componenti meccanici con rivestimento uniforme di nichelatura chimica a basso fosforo ENP 23

Low-phosphorus electroless
nickel plating

The low-phosphorus electroless nickel plating treatment, indicated
in the Deltar procedure as ENP 23, is an autocatalytic
nickel-phosphorus alloy with a P content between 1% and 4% by weight.
It is the process of choice when the component’s priority is mechanical
performance: high hardness of the “as deposited” deposit, resistance
to rubbing wear and dimensional stability over time.

Characteristics of the ENP 23 deposit

Unlike high phosphorus, the ENP 23 deposit offers high mechanical
performance already in the “as deposited” condition, i.e. without
the need for subsequent heat treatment:

High deposit hardness already after deposition
Excellent wear resistance and metal-to-metal contact
Good corrosion resistance in alkaline environments
Corrosion resistance lower than high phosphorus,
but adequate in non-aggressive environments
Thickness uniformity even on complex geometries,
guaranteed by the autocatalytic process

When to choose low phosphorus

Low phosphorus is the correct choice when the component must:

Resist mechanical wear, abrasion and rubbing
Work in dynamic contact with other surfaces
(seats, couplings, threads)
Maintain mechanical performance without
necessarily resorting to post-deposition heat treatments

It is not the optimal choice for components intended for strongly
corrosive environments (aggressive humid, marine, chemical),
where high-phosphorus ENP 1012 is preferable.

Typical applications

Fluid-power and pneumatic components subject to sliding
Moulds for plastics
Precision mechanical components with dynamic couplings
Replacement parts for hard chrome coatings (a more sustainable alternative)
Components for automotive and extrusion
Components for hydrogen production plants

The ENP 23 process
at Deltar

The deposition process takes place chemically, without electric current, through an autocatalytic process controlled in every parameter:

Bath temperature: 85-91 °C
Bath pH: 4.6-5.2
Nickel concentration: 4.5-6.3 g/L
Continuous control of the composition with dedicated electronic instrumentation and daily verification by volumetric titration

The Deltar LS019 procedure complies with the main international standards in the ENP sector: ASTM B117, B183, B322, B499, B571, B578, B602, B636, B656, B689, B733, ISO 4527, MIL-C-26074.

Post-deposition
heat treatments

When required, the ENP 23 deposit can be subjected to heat treatment for two purposes:

Dehydrogenation (ASTM B733 Class 3): eliminates the hydrogen incorporated during deposition, prevents hydrogen embrittlement and improves coating adhesion

Hardness increase (ASTM B733 Class 2): further increases the surface hardness of the deposit with calibrated thermal cycles

Standard quality
controls

Each batch treated with ENP 23 is accompanied by control specimens
(dimensions 50 × 100 × 1 mm in Fe, or supplied by the customer
in a specific material) on which the standard tests are carried out:

Visual inspection
Thickness control (weighing method, ASTM B733 par. 9.3.5)
Adhesion impact test (ASTM B733 par. 9.4.2, ASTM B571)
Burnishing test (ASTM B571 par. 4.1)

On request, additional controls can be carried out: Vickers hardness,
bend test, porosity test (ferroxyl), phosphorus determination,
salt spray (ASTM B117). At the end of processing, Deltar issues
an Inspection Certificate compliant with the EN 10204 3.1 standard.

What is needed for a quick assessment

Technical drawing with areas to be treated and to be protected
Type of base material
Operating conditions (wear, temperature, friction)
Required thickness
Any customer specifications or sector standards

Low-phosphorus electroless nickel plating (ENP 23)

Hardness and wear resistance for mechanical components