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 diffusing them into steel and alloy. In this work, a single high nitrogen face-centered-cubic (f.c.c.) phase (gamma (N)) formed on the 1Cr18Ni9Ti and AISI 316L 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 studied by the electrochemical cyclic polarization measurement in Ringer's solutions buffered to pH from 3.5 to 7.2 at a temperature of 37 degreesC. No pitting corrosion in the Ringer's solutions with pH = 7.2 and 5.5 was detected for the gamma (N)-phase layers on the two stainless steels. The high pitting potential for the gamma (N)-phase layers is higher, about 500 and 600 mV, above that of the two original stainless steels, respectively, in the Ringer's solution with pH = 3.5. The corroded surface morphologies of the gamma (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.