Phase and microstructural study of surface layers produced by plasma immersion ion implantation of stainless steel X6CrNiTi1810

Abstract

A complex study of austenitic stainless steel X6CrNiTi1810 modified by nitrogen plasma immersion ion implantation (PI³) at 300 and 400°C is presented. To obtain detailed information on the structure and phase compositions, conversion electron Mössbauer spectroscopy, XRD, TEM, and Rutherford back scattering spectroscopy are applied. Depending on the treatment temperature a mixture of several phases is observed by Mössbauer phase analysis and confirmed by TEM. The dominant component in specimens treated at 300°C is a paramagnetic oversaturated austenitic phase. A higher implantation temperature (400°C) evokes more pronounced diffusion of nitrogen into the specimen volume, causing a decrease of nitrogen concentration but an increase of stress in the surface layer. This influences the defect density and results in a change of the expanded austenitic phase. Nitride formation is also different depending on the temperature. Furthermore, a texturing of the grains is observed after the PI³ treatment at both temperatures.