Hydrogen blistering under extreme radiation conditions

Radiation damage: surface oxide cracking decreases blistering Irradiation causes hydrogen blisters at metal surfaces as protons recombine with free electrons-except when the surface oxide degrades. A group led by Maciej Sznajder at the University of Zielona Gora in Poland irradiated a thin film of aluminium using a linear proton accelerator at the German Aerospace Center in Bremen. Unexpectedly, the films receiving the largest number of protons blistered the least. This behaviour was due to the aluminium oxide film at the metal surface, which degraded and cracked under higher irradiation. This increased the hydrogen permeability of the aluminium film, leading to less recombined hydrogen and therefore reduced blistering. Research into hydrogen blistering under proton irradiation may help up better understand metal ageing and the effect of surface oxides on Earth and in space. Metallic surfaces, exposed to a proton flux, start to degradate by molecular hydrogen blisters. These are created by recombination of protons with metal electrons. Continued irradiation progresses blistering, which is undesired for many technical applications. In this work, the effect of the proton flux magnitude onto the degradation of native metal oxide layers and its consequences for blister formation has been examined. To study this phenomenon, we performed proton irradiation experiments of aluminium surfaces. The proton kinetic energy was chosen so that all recombined hydrogen is trapped within the metal structure. As a result, we discovered that intense proton irradiation increases the permeability of aluminium oxide layers for hydrogen atoms, thereby counteracting blister formation. These findings may improve the understanding of the hydrogen blistering process, are valid for all metals kept under terrestrial ambient conditions, and important for the design of proton irradiation tests.