Electroless Nickel Coating

BASICS

The Electroless Nickel coating is a process for the functional coating of ferrous and non-ferrous materials.
The process consists in electroless deposition without any external source of electricity. In this process the workpiece is immersed into an aqueous process solution with a specific content of nickel ions. During the process these ions are reduced into metallic nickel. The chemical reacting agents and formulators of the electrons required in this process are the hypophosphite ions in the solution. These agents are transformed, by oxidation in the course of the reaction, into orthophosphate. A nickel-phosphorus alloy layer forms on the workpiece’s surface. This layer effectively protects the workpiece against wear and corrosion.

Electroless Nickel coatingline with pre-treatment and main processing sections.

PROPERTIES

The Electroless Nickel coating is ideal for the functional coating of metals. The properties of the layer range from chemical resistance, dimensional accuracy, excellent anti-friction behavior, electrical conductivity to outstanding hardness. In addition, the coating ensures uniform layer formation true to the original contours. The layer is the ideal solution for the plating of even geometrically complex workpieces with sharp edges and impressions, accessible cavities or bores.

The cross-section illustrates the uniform Electroless Nickel layer on an M4 thread.

The coating’s wear and corrosion resistance depends on the layer's phosphorous content. This content can be increased or reduced depending on the electrolyte’s composition and it can be varied under specific process conditions. Even the layer thickness affects the coating’s resistance: layers with a thickness in the 2 to 10 µm range are resistant to mild corrosion loads, while those in the 5 to 10 µm range are resistant to mild wear loads. A moderate degree of resistance requires layers with a thickness in the 10 to 25 µm range, while severe and very severe loads require thickness values ranging from 25 to 50 µm and over 50 µm respectively.

MATERIALS

Electroless Nickel process can coat almost any metal.

All low-alloy ferritic steels
cast iron-based materials
Stainless steel
Non-ferrous metals (copper, brass, …)
Aluminium alloys
Titanium-based materials
Magnesium alloys
Sintered metal materials

Other metal and ceramic materials can also be coated after performing trials on samples.

APPLICATIONS

The great variety of properties offered by the Electroless Nickel coating and the wide array of suitable materials make the coated workpieces perfect for use in the most diverse sectors.

Mechanical engineering
Fittings construction
Automotive industry
Mining
Office and data technology
Chemical industry
Printing machines
Railway engineering
Electronics
Electrical engineering
Energy and reactor engineering
Aircraft industry
Household appliance industry
Hydraulic and pneumatic components industry
Communications technology
Food processing industry
Measuring and control technology
Pharmaceutical and medical device engineering
Textile machinery construction
Defense industry

Electroless nickel coating for various machinery parts.

Aluminum bike cassette using Electroless Nickel for abrasion resistance.

Part for plastic injection machine with a 30µm layer.

The DNC 520 process variant produces an especially corrosion and wear resistant layer with a phosphorous content ranging between 9 and 13 percent. These layers are suitable for pump housings and stopcocks for use in the natural gas and crude oil sectors, for machines in the food processing industry as well as for nozzles, compressors or screw threads in the automotive industry, transmission engineering, electric engineering and electronics.

Elongation at break

the layer shows an elongation at break in the order of 0.5 to 1.0 percent after measuring foils using the dome method.

Abrasion

abrasion amounts to ≤ 35 mg. after 1,000 revolutions in the Taber-Abraser test using CS 10 wheels.

Hardness

the hardness amounts to about 570 HV 0.05; heat treatment increases the hardness up to about 1,000 HV 0.05.

Corrosion resistance

for instance, a layer with a thickness of 40 µm and roughness of Rz von ≤ 1 µm applied on a St 52 base material resists more than 200 hours in the acetic acid salt-spray test according to DIN EN ISO 9227. In the Kesternich test according to DIN 50 018, the same layer can resist for more than 3 cycles SFW 0.2.