Changes in austenitic steel surface induced by thermal and implantation treatments studied by Moessbauer spectroscopy

Abstract

The surface properties of austenitic (fcc) stainless steel samples in the as-prepared and implanted states were studied. The surface modification was done by plasma immersion ion implantation in methane. This process, done at a temperature of 400 °C in a short time of 3 h, facilitates the enrichment of the steel surface by a higher carbon content. It reaches about 7 at% C in the top surface layers (∼500 nm) and decreases to the nominal value at approximately 10 µm. The thermal annealing treatments of the as-prepared and implanted samples, done at temperatures of 300–500 °C and in time steps of 2–4–8–16–32 h, yielded changes in the elemental distribution and phase composition, which could be followed in the top surface layers of approximately 300 nm using conversion electron Mössbauer spectroscopy (CEMS) and for a surface depth down to 30 µm, by g-ray Mössbauer spectroscopy in the scattering geometry (g-BMS). Complementary results were obtained from glancing-angle X-ray diffraction.