Effects of compositional and structural change on the corrosion behaviour of nitrogen implanted Zircaloy-4

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1999-04, Vol.263 (1), p.23-31
• Main Authors: Lee, S.J., Kwon, H.S., Kim, W., Choi, B.H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Corrosion; Corrosion tests; Exact sciences and technology; Ion implantation; Metals. Metallurgy; Nitrogen; Pitting potentials; Zircaloy-4; ZrN
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(98)01036-3

The influence of nitrogen implantation on the corrosion behaviour of Zircaloy-4 was examined by potentiodynamic polarization tests in a chloride and an acid solution, and the results were discussed with structural and compositional variations of implanted layer that was determined by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The resistance to localized corrosion of Zircaloy-4 was very sensitive to the ion dose and the substrate temperature during the implantation. At substrate temperatures above 200°C, the pitting potential of the nitrogen implanted alloy in deaerated 4 M NaCl at 80°C increased gradually with the ion dose from 350 mV SCE for the unimplanted sample to 990 mV SCE for the alloy implanted with an ion dose of 6×10 17 ions cm −2, and then the alloy was immune to pitting when implanted with ion doses greater than about 1×10 18 ions cm −2. In contrast to this, the alloy implanted at 100°C exhibited an inferior corrosion resistance to the unimplanted sample irrespective of the ion dose. A drastic increase in the resistance to pitting corrosion in chlorides as well as a significant reduction in the passive current density in acid solution of the implanted alloy, were found to be associated with the formation of ZrN layer with a stoichiometric ratio of N to Zr. The low resistance to localized and general corrosion of the alloy implanted at 100°C was attributed to the increase in structural defects produced by ion bombardment, and to low atomic mobility in the implanted layer.