Stainless steel is widely used as implant material in orthopedics [1]. One problem is to reduce the corrosionrelated release of undesirable metal ions from the alloy [2, 3]. Surface coatings [4] are the common way to improve the corrosion resistance. The present work studied the corrosion behavior of coatings on austenitic stainless steel (ASS) 304L produced by plasma immersion ion implantation (PIII) of nitrogen [5]. In this method negative high voltage pulses are applied to a target immersed in nitrogen ions containing plasma. The nitrogen ions are accelerated through the plasma sheath and implanted into the target surface. Samples under study were discs of 304L ASS (25 mm diameter and 3 mm thickness), polished with SiC abrasive paper and diamond paste, followed by a standard cleaning, and subjected to nitriding by plasma immersion ion implantation of 1 × 1016 N2 /cm2 at 10 keV using the facilities at the Forschungszentrum Rossendorf, Germany. Other process parameters for PIII used were 2 × 10−3 Pa base pressure, 0.2 Pa work pressure, 400 w RF power, 5 μs pulse, 3.0 A current peak (32 mA/cm2), and for 1 h duration. Electrochemical measurements were conducted with an AutoLab PGSTAT 12 and the GPES software (Eco Chemie, The Netherlands). A three-electrode electrochemical cell was used with a saturated calomel reference and a Pt counter electrode. The electrolyteexposed area was 0.07 cm2. The potential scan rate was 10 mV/s. All measurements were made in aerated 1 w% NaCl solution at 25 ◦C. The surface topography was characterized using atomic force microscopy (DS 45–40 from DME). The images were collected in the AC mode (300 kHz resonance frequency) at a scan rate of 3–5 Hz employing Si3N4 catilever tips (42 N/m force constant). Results of potentiodynamic polarization are shown in Fig. 1 comparing the behavior of ASS surface before (reference surface) and after PIII treatment (PIII surface). Both surfaces behave qualitatively similarly. On the cathodic side an activation polarization occurs within a narrow potential region around the corrosion potential. This region is followed by an extended passive region with nearly constant current. At more anodic