Effect of ion energy and chemistry on layer growth processes during nitriding of CoCr alloys

Nitriding of metals is a complex process, governed by surface reactions, transport from the surface to the bulk, normally through a surface oxide, and diffusion in the bulk. Using energetic ions, the first two steps are circumvented, as the ions are directly deposited behind any surface barrier. By comparing gas nitriding, plasma nitriding with an ion energy of less than 5 eV and plasma immersion ion implantation (PIII) at 10 kV pulse voltage, it was shown that a dissociative adsorption, enhanced by low energy ions is occurring during nitriding processes of CoCr alloys. A strong dependency on the alloy composition and the chemistry of the surface oxide layer was observed.