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Fig. 6. 7 Salt bath nitriding

6.3.3 Plasma Nitriding

Process description
Plasma nitriding/ion nitriding is a modern thermochemical treatment which is carried out in a mixture
of nitrogen, hydrogen and an optional carbon spending gas.
In this low pressure process, a voltage is applied between the batch and the furnace wall. Plasma is
formed in a vacuum using a high-voltage electrical energy to accelerate nitrogen ions which bombard
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the alloy surface. A glow discharge with a high ionization level (plasma) is generated around the parts.
On the surface area that is directly charged by the ions, nitrogen-rich nitrides are formed and
decompose, releasing active nitrogen into the surface. Due to this mechanism shielding is easily done
by covering the concerning areas with a metal blanket. Plasma nitriding allows modification of the
surface according to the desired properties. Tailor made layers and hardness profiles can be achieved
by adapting the gas mixture: from a compound layer-free surface with low nitrogen contents up to 20
microns thick, to a compound layer with high nitrogen contents and an add-on of carbonic gas (plasma
nitro-carburation). The wide applicable temperature range enables a multitude of applications, beyond
the possibilities of gas or salt bath processes (Fig. 6. 8).

Fig. 6. 8 Plasma nitriding process
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scheme

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