Surface Hardening of an FeCrNiAl Alloy by Ion Nitriding

Surface hardening of a FeCrNiAl alloy by the ion nitriding method has been investigated. This alloy was originally developed for applications as cutting tools and its surface is hardened by the alumina layer produced by heat-treatment at a high temperature between 1373 and 1573 K. This heat-treatment, however, tends to cause deformation of the alloy. Thus has been explored the surface hardening of the FeCrNiAl alloy by the ion nitriding method which is thought to be suitable for hardening the alloy surface at a lower temperature avoiding deformation of the alloy. The obtained results are as follows: (1) CrN, ε-Fe2∼3N, Fe4N and AlN are formed near the surface of the FeCrNiAl alloy resulting in the increase of the surface hardness. (2) Vickers hardness of the nitrided layer ranges from 12.0 GPa to 13.5 GPa as the result of ion nitriding at various temperatures from 773 to 873 K. (3) Thickness of the nitrided layer changes with nitriding duration and temperature. The thickness of the nitrided layer is roughly proportional to the square of the nitriding duration. (4) Corrosion resistance after the nitriding treatment is lower than that before the nitriding treatment.