Fitting corrosion resistance of high nitrogen f.c.c. phase in plasma source ion nitrided austenitic stainless steel

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 metal and alloy. In this work, 1Cr18Ni9Ti (18-8 type) austenit ic stainless steel was treated at a process temperature of 380 degreesC dur ing a nitriding period of 4 h. A single high nitrogen f.c.c. phase (gamma ( N)) with a high nitrogen concentration of 32 at.% was characterized using A uger electron spectroscopy, electron probe microanalysis, glancing angle X- ray diffraction, and transmission electron microscopy. The pitting corrosio n resistance of the gamma (N) phase layer was measured by cyclic polarizati on in a series of 3% NaCl solutions buffered to pH from 0.4 to 13. In the p otential-pH diagram of the gamma (N) phase layer, the extended immunity and perfect passivity zones and the narrowed imperfect passivity and pitting z ones were obtained, compared with that of the original austenitic stainless steel. No pitting corrosion resistance was observed for the y, phase layer in the solutions of pH 4-13. The high supersaturation of nitrogen in the y , phase led to the improvement in the pitting corrosion resistance. (C) 200 0 Elsevier Science B.V. All rights reserved.