Effect of ions implantation on the oxidation of Ni-32Cr-10Fe Alloy in PWR primary media: role of surface defects on the corrosion mechanisms

Ni-based alloys constitute the main components for steam generator tubes in pressurized water reactors (PWR). Their surface state, and more particularly the presence of structural defects, for instance due to work-hardening, is a key parameter for the oxidation process since superficial damages influence the morphology of the so-formed oxide scale as well as its growth kinetics. In order to simulate different defective sub-surface states, ions implantation experiments, well-known to provoke controlled structural damages in materials, have been set up on alloy 690 samples. The first results, dealing with Xe implantation, highlight the twofold effect of superficial defects on oxidation. On the one hand, they change the crystallinity of the continuous spinel oxide layer, increasing the density of short circuits. On the other hand, they promote the nucleation frequency of chromia nodules at the oxide/alloy interface. The ongoing work based on Nix+ implantation in Alloy 690 aim to give more insights on oxidation mechanism in the case of damaged surface enabling thereafter the modelling of corrosion process.