Plasma immersion ion implantation for diffusive treatment

Plasma-immersion implantation is described as a technique providing high kinetic energies and, thereby, high penetration
depths of atoms injected for surface modification. In connection with ion sputtering, this may create favourable boundary conditions for the efficiency of diffusive surface treatment such as nitriding. The influence of surface layers such as oxides on the nitriding process is discussed and demonstrated for stainless steel by a model experiment employing low-energy nitrogen implantation and real-time in situ surface diagnostics. It is shown that the surface oxide acts as a barrier for diffusive nitrogen transport. The evolution of the nitrogen profiles can be described reasonably well by diffusion under the influence of traps. Examples of nitrogen profiles obtained by plasma-immersion nitriding show depths of the nitrogen-rich phases of up to 50 micrometer and 15 micrometer in stainless steel at 380°C and aluminium at 500°C, respectively.