Plasma nitriding, also known as ion nitriding, is a physical phenomenon in which nitrogen is ionized to form a "sheath" on the surface of the parts. This heat treatment method is primarily used to increase the resistance of parts to wear, abrasion, fatigue and seizure, and consequently to improve their hardness. Ion nitriding offers a number of advantages, and is far less energy-intensive than other techniques, not least because it can be carried out at very low temperatures. It is therefore both an economical and environmentally-friendly process.
What is plasma nitriding?
Also known as ion nitriding, plasma nitriding is highly effective in increasing the surface hardness of steel parts, while improving their resistance to wear, friction, fatigue, abrasion and seizure.
This physico-chemical process consists in ionizing a gas, a phenomenon quite similar to the way neon lights work. To trigger the reaction required to produce light, the neon gas passes between an anode and a cathode, where it is ionized and then subjected to a glow discharge.
In the case of plasma nitriding, nitrogen is ionized between an anode and a cathode, i.e. it changes from the form of a single N2 molecule to that of two positively charged ions, N+, and two electrons. This electromagnetic phenomenon can take place at room temperature, as molecular nitrogen begins to decompose in the plasma as early as 20 degrees Celsius.
3 plasma nitriding methods
In fact, plasma nitriding as practised by the THERMILYON Group covers three different processes:
- direct plasma
- additional heating technology
- theAS¨PN
The first method is still the most traditional, and involves applying plasma to the surface of the part. This plasma both heats the part and produces nitrogen ions.
Additional heating involves separating the ion bombardment to ionize the nitrogen from the heating of the element to be treated. In this context, the part is not heated by the bombardment itself, but independently.
Finally, ASPN, for Active Screen Plasma Nitriding, represents a so-called post-discharge system, where the plasma is not applied directly to the material, but to a screen. This technique limits the risks associated with plasma on the part itself, such as the appearance of electric arcs or differences in part shape.
Why ion nitriding?
Plasma nitriding has the significant advantage of being carried out at a very low temperature. As a result, the process only consumes electricity, and less of it than other chemical treatments. What's more, this technology seems ideally suited to parts with complex geometries and treatment sparing, as simple metal covers are sufficient to prevent the treatment of certain special areas.
Energy-efficient technology
Since nitrogen can start to decompose into plasma as early as 20 degrees Celsius, the ion nitriding process can take place in a lower-temperature atmosphere than other techniques. For example, while gas nitriding takes place in environments heated to over 500 degrees, some steels can be nitrided at around 400 degrees using plasma nitriding.
This method takes place in a vacuum atmosphere, and therefore uses very little process gas. On average, it is estimated that ion nitriding consumes around 10 times less process gas than other atmospheric heat treatments, making it a particularly economical solution, both for the wallet and the environment. Indeed, consuming less also means discharging less, making plasma nitriding more eco-friendly than some other processes requiring very high temperatures or larger quantities of process gas. Ion nitriding also uses no chemicals.
The ideal solution for complex geometries with savings
In addition to being a more energy-efficient solution, plasma nitriding is ideal for parts with specific geometries. Since plasma nitriding is an electromagnetic phenomenon, the areas to be protected from treatment can simply be covered by metal covers. For example, in the case of a tapped hole on a part to be treated, a screw plugging the opening prevents the inside from being nitrided during the process.
This solution seems much simpler to implement than its equivalent in the context of gas nitriding, where the areas to be preserved have to be coated with a special paint, applied by hand. On the other hand, to process parts of sometimes imposing dimensions, suitable furnaces are required, which is why Thermi Lyon has a 6-meter-long furnace at its Lyon site, designed to accommodate large parts.
Plasma nitriding has many virtues, improving the resistance of materials to wear, fatigue, galling and abrasion, while increasing their hardness. It consumes considerably less energy than most other heat treatments, and is therefore more economical, both for budgets and for the planet. What's more, it makes it easy to treat parts with complex geometries that don't require comprehensive treatment. This method is increasingly used in the aeronautics sector, in particular, as it enables the nitriding of stainless steel alloys. It is also widely used in metalworking and food processing machinery, which work in highly abrasive environments.
