Phase formation and corrosion behavior of nitrogen implanted Zr–Sn–Nb alloy in alkaline environment

Fretting induced corrosion occurring at the tube–grid contact is a very important problem for cladding materials and ion implantation has been considered an effective technology capable of improving the corrosion resistance of fuel cladding material without noticeably changing in dimensional integrity. In this paper, Zr–Sn–Nb specimens were implanted by nitrogen with fluence range from 5 × 1016 to 4 × 1017 ions/cm2, and then subjected to electrochemical study in a solution with pH = 10 in order to determine the optimum fluence that can give good corrosion resistance in a simulated nuclear reactor condition. Glancing angle X-ray diffraction (GAXRD) was employed on the implanted to understand phase formation with increasing fluences. The depth profile of the oxides in the scale was analyzed by Auger electron spectroscopy (AES). The results showed the corrosion resistance of Zr–Sn–Nb was sensitive to the ion fluence and the substrate temperature during the implantation. The alloy implanted at below 473 K exhibited an inferior corrosion resistance to the unimplanted sample irrespective of the ion fluence. A drastic increase in the resistance to pitting corrosion in alkaline 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 worse corrosion resistance of the alloy implanted at below 473 K may be attributed to the increase in structural defects produced by ion bombardment.