Application of RBS and NRA for the Investigation of Corrosion Resistance of Nitrogen‐Implanted Steel.

Abstract

Austenitic stainless steel AISI 304L was implanted with low energy, high current nitrogen iοns at moderate temperatures extracted from a Kaufman type iοn source (Extraction voltage: 1.2 keV; Extracted current: 1 mA/cm2; Ion dose: about 4x1019 ions /cm2). The temperature during the implantation (duration 1 hour) was 400 and 500 oC respectively for the two series of samples prepared. The characterization of the samples by X‐Ray Diffraction, Transmission Electron Microscopy and Scanning Electron Microscopy showed that a metastable fcc solid solution with a high nitrogen content (about wt. 30%) was formed resulting in an increase of its Vickers hardness. Rutherford Backscattering Spectrometry (Ed: 1.75 MeV) was applied in combination with Nuclear Reaction Analysis (NRA) in order to obtain information about the N‐, O‐ and C‐ depth distribution in the near‐surface layers of the samples. The nitrogen depth distribution was determined using the 14N(d,α)12C and the 14N(d,p)15N nuclear reactions whereas the oxygen and carbon ones by the 16O(d,p)17O and 12C(d,p)13C (Ed: 1.35 MeV). Investigation of the corrosion behaviour of the samples was performed under strong aggressive conditions (hydrochloric acid 2% at 50 oC) using electrochemical techniques (potentiodynamic polarization and cyclic voltammetry). The samples implanted at 400 oC exhibited remarkable resistance to corrosion compared to those implanted at 500 oC and the untreated material. This could be attributed to the modified surface region and its high nitrogen content.