Duplex Coatings - Lesson 2: Plasma nitriding of tool steels
Welcome back to the Ionbond Summer School!
Today, we are diving into the plasma nitriding process. What is it exactly?
Plasma nitriding: a treatment, not a coating
Plasma nitriding is an important step in the creation of a duplex coating, but it is not a coating in itself. It belongs to the group of thermo-chemical diffusion treatments. These are thermal treatments that take advantage of diffusion of atoms from the surrounding plasma into the solid tool to change its chemical composition. The aim is to optimize the materials’ microstructure characteristics, which have a significant influence on the tool’s performance in production.
See below two cross sections of D2 cold work steel after plasma nitriding.
Heat treatment performed under vacuum
Specifically, plasma nitriding is a thermo-chemical surface heat treatment performed under vacuum and driven by diffusion.
Surface heat treatment
It is a surface heat treatment, which means it is used in situations where the surface layer needs to have a higher hardness and be more wear resistant than the core.
Diffusion
Diffusion is the movement of species (atoms, ions, molecules, etc.) from a region of higher concentration to a region of lower concentration. Therefore, it is always driven by a gradient in concentration.
During plasma nitriding, nitrogen is brought to an ionized gas state (plasma) so it can diffuse into the surface of the tool. It is a low-temperature process with temperatures between 400 and 600 °C.
Now you know what plasma nitriding is, you are ready for the next lesson: more detail about the different layers that arise during plasma nitriding, and what the benefits and drawbacks are.
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