The characteristics of surface oxidation and corrosion resistance of nitrogen implanted zircaloy-4

This work is concerned with the development and application of ion implantation techniques for improving the corrosion resistance of zircaloy-4. The corrosion resistance in nitrogen implanted zircaloy-4 under a 120 keV nitrogen ion beam at an ion dose of 3 x 10(17) cm(-2) depends on the implantation temperature. The characteristics of surface oxidation and corrosion resistance were analyzed with the change of implantation temperature. It is shown that as implantation temperature rises from 100 to 724 degrees C, the colour of specimen surface changes from its original colour to light yellow at 100 degrees C, golden at 175 degrees C, pink at 300 degrees C, blue at 440 degrees C and dark blue at 550 degrees C. As the implantation temperature goes above 640 degrees C, the colour of surface changes to light black, and the surface becomes a little rough. The corrosion resistance of zircaloy-4 implanted with nitrogen is sensitive to the implantation temperature. The pitting potential of specimens increases from 176 to 900 mV (SCE) as the implantation temperature increases from 100 to 300 degrees C, and decreases from 900 to 90 mV (SCE) as the implantation temperature increases from 300 to 640 degrees C. The microstructure, the distribution of oxygen, nitrogen and carbon elements, the oxide grain size and the feature of the precipitation in the implanted surface were investigated by optical microscope, TEM, EDS, XRD and AES. The experimental results reveal that the ZrO2 is distributed mainly on the outer surface. The ZrN is distributed under the ZrO2 layer. The characteristics of the distribution of ZrO2 and ZrN in the nitrogen-implanted zircaloy-4 is influenced by the implantation temperature of the sample, and in turn the corrosion resistance is influenced. (C) 1997 Elsevier Science S.A.