Effect of Mo and Mo+N implantation on corrosion resistance of austenitic stainless steel

Abstract

A study has been made of the effects of Mo and Mo + N implantations on the corrosion resistance of AISI 304L stainless steel. Mo ion implantation was performed with doses ranging from 1 × 10 14 to 3 × 10 17 Mo cm −2 at an acceleration voltage of 65 kV, using an MEVVA IV 80-10 implanter. N ion implantation into some Mo-implanted specimens was carried out with a dose of 1 × 10 17 N cm −2 at 65 kV. The corrosion resistance of the implanted steel was investigated by an electrochemical method in 0.5 M H 2SO 4, 0.5 M HCl and 0.6 M NaCl solutions. After both Mo and Mo + N implantations, the free corrosion current density ( I corr) decreased and the breakdown potential ( E b) increased in HCl. Their modification effects saturated with the very low dose of 1 × 10 14 Mo cm −2. Following 1 × 10 17 N cm −2 implantation, the critical and passive current densities in the acid solutions of H 2SO 4 and HCl also declined at the very low dose of 1 × 10 14 Mo cm −2, and increased at a dose of 1 × 10 16 Mo cm −2. These results indicated that Mo + N double ion implantation with a very low Mo dose is useful for improving the corrosion resistance of 304L stainless steel under acidic conditions. In the neutral solution of NaCl, both the I corr and E b characteristics for the 304L stainless steel modified by Mo and Mo + N implantations improved with increasing Mo dose; the improvement caused by Mo + N double ion implantation tended to be greater than that for Mo single ion implantation. In conclusion, we propose that Mo + N double ion implantation into 304L stainless steel can be expected to form a surface resistant to various corrosion conditions, depending on the choice of implantation dose of Mo ions.