Question: What causes the white layer (compound layer) to form during the plasma-nitride process?

Answer: The white layer formation is a function of:
  • Process gas ratios
  • Processed steel chemistry
If the process gas chemistry is mixed, with 1/3 being Nitrogen and 2/3 being Hydrogen, the surface metallurgy of the compound layer will be approximately (depending on the steel composition) 10% of the TOTAL formed case.

If the process-gas chemistry is changed (as can be quite easily with plasma nitriding) then the surface – compound layer – can also be changed. Conventional gas nitriding relies on the Floe process – two-stage nitriding – to reduce the thickness of the compound layer. This involves temperature and gas dissociation changes. Whereas with plasma nitriding, it is simply a change in gas ratios in relation to the steel being treated.