In vitro corrosion resistance of plasma source ion nitrided austenitic stainless steels

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusi ng them into steel and alloy. In this work, a single high nitrogen face-cen tered-cubic (f.c.c.) phase (gamma (N)) formed on the 1Cr18Ni9Ti and AISI 31 6L austenitic stainless steels with a high nitrogen concentration of about 32 at % was characterized using Anger electron spectroscopy, electron probe microanalysis, glancing angle X-ray diffraction, and transmission electron microscopy. The corrosion resistance of the gamma (N)-phase layer was stud ied by the electrochemical cyclic polarization measurement in Ringer's solu tions buffered to pH from 3.5 to 7.2 at a temperature of 37 degreesC. No pi tting corrosion in the Ringer's solutions with pH = 7.2 and 5.5 was detecte d for the gamma (N)-phase layers on the two stainless steels. The high pitt ing potential for the gamma (N)-phase layers is higher, about 500 and 600 m V, above that of the two original stainless steels, respectively, in the Ri nger's solution with pH = 3.5. The corroded surface morphologies of the gam ma (N)-phase layers observed by scanning electron microscopy are consistent with the results of the electrochemical polarization measurement. (C) 2001 Elsevier Science Ltd. All rights reserved.