ENHANCED PITTING CORROSION-RESISTANCE OF 304L STAINLESS-STEEL BY PLASMA ION-IMPLANTATION

High-nitrogen, austenitic stainless steels combine a variety of superi or mechanical properties with an increased resistance to localized pit ting/crevice corrosion in halide environments. However, nitrogen conte nt in the bulk is restricted during normal melt/solidification process es due to limited solubility, which, if exceeded, leads to nitride for mation and possible sensitization. Plasma ion implantation (PII) techn iques may result in much higher nitrogen contents via nonequilibrium s urface modification. PII of nitrogen into 304L stainless steel, and it s subsequent effect on the pitting corrosion of this alloy, has been i nvestigated. The implantation process at the University of Tennessee M icrowave Plasma Facility results from a large-volume (206 l), steady-s tate, uniform plasma, generated by up to 2 kW of 2.45 GHz microwave po wer. Samples were negative pulse biased to potentials of 10 and 20 kV, with doses ranging from 10(14) to 10(18) ions/cm2. Rutherford backsca ttering spectroscopy analyses of dose uniformity and depth profiling w ere also conducted. Potentiodynamic anodic polarization behaviors were determined in a deaerated 1.0 wt % NaCl solution. The highest pitting potentials, up to 1440 mV (standard hydrogen electrode) were measured at the lowest range of doses. These results indicate that nitrogen do ses effective for tribological enhancement may be incompatible with th ose effective in resisting localized corrosion.