• Picture of a plasma during nitriding in an ASPN furnace

    Plasma nitriding process

    Plasma nitriding uses plasma discharge physic to diffuse nitrogen into the surface of a ferrous alloy.

Plasma nitriding


What is plasma nitriding ?

Plasma Nitriding known also as ion nitriding is a form of case hardening process. It is a heat treatment process which diffuses nitrogen into the surface of a metal to create a case-hardened surface.

Plasma nitriding uses plasma discharge physic to diffuse nitrogen into the surface of a ferrous alloy.

The plasma nitriding process starts by pumping the atmosphere of the furnace chamber until the desired vacuum pressure. Then a gas mixture typically made of nitrogen and hydrogen is introduced into the chamber. A voltage difference is applied between the wall of the furnace and the parts. Due to this difference of potential and to the low pressure the gas is ionized. Ion bombardment will have the double effect of cleaning the parts and also increase the temperature up to the nitriding temperature generally between 500 and 580°C.

The generated plasma envelops the surface of the product with a blue-violet glow. Depending on the nitriding temperature and gas mixture nitrogen will react with the steel to form a diffusion layer and a compound layer made of two phases:

  • Epsilon, Fe2-3N
  • Gamma prime Fe4N

Depending on the application the process is tuned to form the desired phase.


ASPN - Active Screen Plasma Nitriding

ASPN is a new industrial solution that enjoys all the advantages of DCPN but does not have its inconveniences.

The active screen acts as a radiation heater and as there is no direct glow discharge at the component, there is no overheating happening and any effect caused by the electrical field is eliminated. This enables proper temperature control and uniformity and allows mixing of parts with different dimensions with the same time - which increases the process efficiency [up to 50% more load density]. Even semi bulk loads can be treated uniformly and efficiently which is not possible with the DCPN process.    

Different-size parts can be treated in the same batch. It also offers the possibility of nitrocarburizing and nitriding of stainless steels.

ASPN has the following advantages:

  • Simple process control
  • Sintered parts can be nitrided
  • Possibility of partial nitriding surfaces
  • No Ammonia consumption
    • but a mixture of N2 and H2
  • Low energy consumption
  • Low gas consumption
    • about 200Nl/h : at least 90% lower than for gas nitriding
  • No poisonous consumable and waste
  • Very large range of applications
  • Solves most problems of the common plasma nitriding technology (DCPN)
    • Prevents hollow cathode effect
    • Prevents arking issues
    • Prevents edge effect
    • Good temperature uniformity
  • High development potential

The ASPN technology is covered by the ION2-cloud® patent exclusively owned by ALD


DCPN – Direct Current Plasma Nitriding

DCPN is the historical way to nitride with plasma which has the following advantages:

  • Sintered parts can be nitrided
  • Possibility of partial nitriding surfaces
  • No Ammonia consumption
    • but a mixture of N2 and H2
  • Low energy consumption
  • Low gas consumption
    • about 200Nl/h : at least 90% lower than for gas nitriding
  • No poisonous consumable and waste

However, DCPN process also has limitations which are mainly based on the effects resulting from the formation of an electrical field, as:

  • "Hollow-cathode"
    • Effect when parts are placed very close together or if they contain deep holes of small diameter, the overall discharge current can increase so much so that local melting takes place, proper loading is an issue
  • Arking
    • Arking can produce very high local temperatures and cause localized melting and/or sputtering of material from this point on the surface. This effect could happen by organic degassing in a localized area of a component's surface, by the presence of non-metallic inclusion in the work piece material > a perfect degreasing of the parts is needed
  • Edge" effect
    • Effect with components containing sharp corners or of complex geometries, can cause different nitriding effects and brittleness risk
  • Bad temperature control and uniformity
    • Is an issue to treat components with different cross sections and does not allow to run mixed loads with different part sizes and geometries

More about nitriding processes

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