Corrosion behavior of nitrogen-implanted zircaloy

Abstract

Nitrogen implantation was applied to Zircaloy-4 sheet to improve corrosion resistance at 100 and 120 keV by varying the ion dose of nitrogen from 1 x 10(17) to 1 x 10(18) ions cm(-2). The influence of nitrogen dose and substrate temperature on the corrosion resistance of the alloy were examined by measuring potentiodynamic anodic polarization curves in deaerated NaCl solution at 80 degrees C. The corrosion resistance of Zircaloy-4 was significantly improved with nitrogen implantation, as confirmed by the distinct increase in the pitting potential from 235 mV (vs, saturated calomel electrode, (SCE)) for the unimplanted alloy to 685 mV(SCE) for the alloy implanted with 10(18) ions cm(-2), and by the gradual decrease in the passive current density with dose. This improvement in corrosion resistance of the implanted alloy is attributed to the formation of ZrN and ZrO2 during the implantation. Corrosion resistance of nitrogen implanted Zircaloy-4 was found to be very sensitive to the substrate temperature; the maximum resistance to localized corrosion of the implanted alloy was obtained at about 293 degrees C.