Factors Affecting the Corrosion Resistance of Materials under Irradiation in the Early Stage of Growth of the Passive Films

Abstract

The protective character of the passive films growing on either pure metals or alloys is largely modified either under or after irradiation, i.e. as observed during in-situ or ex-situ electrochemical tests respectively. In irradiation experiments, the projectile loses its energy in the target by nuclear collisions and various electronic excitation processes, depending on the projectile - target couple, on the energy, flux and fluences considered. The electronic and/or ionic transport properties in the passive films can be affected by irradiation, depending on the test conditions. The changes in the electronic properties of the anodic films of titanium after ion-implantation are first briefly reviewed, i.e.under conditions of both nuclear and electronic stopping. When the target is a metal electrode whose back face is bombarded with alpha particles and front face is exposed to the corrosive aqueous medium, the energy deposited by the alpha particles in the target by electronic excitations can be a priori divided between the solid and the liquid phase, the passive film growing at the metal/solution interface being considered as part of the solid phase. The respective influence of radiations on the film and solution side of the passivated material/corrosive aqueous medium interface is discussed for two different types of materials, a 304 stainless steel and pure titanium passivated under alpha-irradiation. Only the early stage of growth of the passive film is considered. A reactivating or a passivating influence of alpha-radiations is evidenced, depending on the energy range of the alpha-particles, under electrochemical conditions “not corrosive enough” to produce this effect without irradiation (room T, dilute acidic aqueous solution).