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Plasma Nitriding - The today importance for heat treatment
2008-12-15 11:01:39

Plasma nitriding techniques are known for a long time and have been developed industrially for about 40 years, to say since the 70ies. But in numerous countries this development remained rather poor due to some major difficulties inherent to the process of this innovative technology.


The main problems are listed below.

- risk  of electric arcing,
- risk of over heating due to the so called hollow cathode effect,
- difficulties to master the temperature homogeneity in a load,
- loading constraints due to the technology,
- low density loading,
- problems to process parts of different geometries in one single batch,
- the need of skilled operators,
- quite an important know how is a must.

Nowadays this technology meets a true renaissance, a new developing potential thanks to:

1) The enormous progress of ion nitriding equipment:
a) pulsed current power supplies having following main characteristics:

- variable or adjustable frequency (100 - 20.000 kHz.)
- Choice of the pulse shape.
- Choice of the pulse sequence, pause (on - off)
- Choice of positive or negative pulses or a mix of both.
- Plasma power from 20 – 500 kVA.

b) New chamber concepts with additional heating

- Furnace with additional heating by radiation

- improvement of the temperature homogeneity.
- decreasing of the electrical arc risk.
- makes the loading of the chamber easier, various geometries can be treated together.
- the chamber can be filled more densely.

- The active screen technology which is actually the last known step in development and evolution of the plasma nitriding technology. It  brings a true solution to nearly all the problems and obstacles related to the plasma technology.

- The risks of arcing and hollow cathodes are definitively eliminated.
- Good temperature homogeneity.
- Loading density improved, >90% of the chamber volume can be used.
- Mixed loads of geometrically different parts can be treated.
- Semi-bulk treatments become possible.

c) mastering the influent parameters

- treatment time, the pressure, the gas mixtures, the plasma density are nowadays perfectly measured and controlled. This allows fully automatic and fully repeatable treatments, thanks to especially created software. Highly trained and skilled operators are no more a must.

2) Progress in novel treatment for special steels and alloys such as:

- stainless steels, titanium alloys, nickel alloys, cobalt alloys,
- powder technology parts,
- post oxidation.

3) Production costs lower that with the more classic technologies, like salt and gas.

Plasma vs gas:
energy decreased by 15% to 50%
gas consumption decreased by up to 95%

4) Environment

No use of dangerous or polluting gas. ( N2+ H2;…. vs  NH3, salts, …)
Gas types like CO; CO2; NOx… are reduced by >95%

Today, thanks to active screen technology, one can predict a strong development of plasma assisted processes like: nitriding, nitro carburizing, etc.

Author: Dr. Jean-Paul Lebrun