Benefits of Plasma Nitriding Heat Treatment

posted On Thursday, August 4, 2022 in Blog

A modern version of plasma nitriding is UltraGlow® Plasma Nitriding, the process has been practiced by Advanced Heat Treat Corp. (AHT) for over 40 years. The process, also referred to as 'ion nitriding', has its specific benefits allowing it to be more advanced than many other methods [1-5].

Depending on the application, heating of the treated subject can be done by glow discharge only or with the supplementary heat generated by the wall cathodes or its resistance heating elements.

All of those methods allow for controlling plasma density, as needed, for uniform heating and activation of the surface when treating stainless steels components. The method is so-called a “low-nitriding potential method”, which limits growth of the compound zone by the nature of the process itself without special measuring/controlling methods that are needed in gas nitriding [1]. The process can be carried out at a temperature of 350-600+Deg. C (662-1100+ Deg. F) without additional activation of the treated surface. Since the energy of the ions bombarding the cathode/object is up to 200eV, it eliminates any native surface oxides present in the stainless steel.

Popular Applications for Plasma Nitriding

Applications for plasma nitriding are very broad. Examples include treatment of large-sized stamping dies, long objects such as feedscrews and shafts, stainless steels parts as well as low-density powder metal components and many others.

Selected examples of the best applications are shown here; Advanced Heat Treat Corp. treats many stamping dies of significant weight and dimensions. Parts like that usually have quite a few threaded holes, which are easily protected from the treatment by mechanical masking with simple bolts eliminating the contact of these critical surfaces from the glow discharge, see Fig. 2.

 

Large size/length shafts exceeding 30’ are treated quite often plasma nitrided in our shop in Monroe, Michigan, see Fig. 3.

Many low-density, <7.1 g/cm3 products have been plasma nitrided at AHT. Using gas or salt bath nitriding methods in those situations would not be possible or would be very difficult [4, 5]. Properly controlled plasma allows for forming a uniform nitrided layer, even in complex geometry parts, without penetrating the core sections with the active nitrogen containing species such as ammonia used for gas nitriding [4].

Metallographic pictures of cross sections of two different low-density PM plasma nitrided components are shown in Fig. 4. Compound zone (CZ) does not form below the surface which is the case in gas nitriding.

Fig. 4. Photo micrographs of two different PM components showing nitrided layer with a CZ at the surface. Please note absence of CZ in porosities below the surface. White layer at the surface is an aluminum foil used for enhancing the quality of vision at an edge of the sample. Etched with 3% Nital.

It should be noted that plasma nitriding is an environmentally-friendly process using nitrogen and hydrogen gases in quantities much smaller than ammonia used in gas nitriding method.

References

1. E. Rolinski,” Plasma Assisted Nitriding and Nitrocarburizing of Steel and other Ferrous Alloys”, Chapter 11 in Thermochemical Surface Engineering of Steels, Ed. E. J. Mittemeijer and M. A. J. Somers, Pub. Woodhead Publishing, 2014, pp 413-449.

2. E. Rolinski, A. Konieczny, G. Sharp, “Nature of Surface Changes in Stamping Tools of Gray and Ductile cast Iron During Gas and Plasma Nitrocarburizing”, Journal of Materials Engineering and Performance, 2009, Vol. 18 No 8, pp 1052-1059.

3. E. Rolinski, G. Sharp, “When and Why Ion Nitriding/Nitrocarburizing Makes Good Sense”, Industrial Heating, Aug. 2005, pp 67-72.

4. E. Roliński, M. Woods “Plasma Nitriding Mechanisms of Low-Density Sintered Metal Products/Mechanismen des Plasmanitrierens von gesinterten Metallprodukten mit niedriger Dichte”, HTM J. Heat Treatm. Mat. 76 (2021) 1, 2021, pp. 58-63.

5. E. Rolinski, J. Ludeman, J. McCain, V. Popovski and M. Woods, “Nitriding Mechanisms of Ferrous Powder Metal Products in Gas, Salt and Plasma Methods”, Proc. of the International Conference: PowderMet2021/AMPM2021/Tungsten2021, Conference in Orlando, June 2021, Proc. ISBN No. 978-1-943694-27-3 © 2021 Metal Powder Industries Federation 105 College Road East, Princeton, New Jersey 08540-6692 USA , pp. 330-337.

1. edward rolinski
2. ion nitriding
3. nitriding
4. plasma nitriding