IFHTSE Global 21: heat treatment and surface engineering in the twenty-first century Part 14 – Development of compound layer during nitriding and nitrocarburising; current understanding and future challenges

The development of the compound layer during gaseous nitriding and nitrocarburising of Fe based material is described. The first nucleation of the compound layer at the surface depends on the competition between the dissociation of ammonia and the removal of nitrogen from the surface by solid state diffusion and desorption or the competition with a carburising reaction. During compound layer growth, the nitriding kinetics is determined by a combination of solid state diffusion of interstitial elements and the kinetics of the surface reactions. Moreover, phase transformations within the compound layer play a role in determining the overall layer growth kinetics during nitrocarburising.