The formation of hydrogen induced blisters and their growth in nickel pre-implaned with helium

The applications of the fusion reactor raise new and exciting difficulties regarding helium behavior in metals. There are several ways that helium will be formed in the first wall of these reactors. The main ones are severe α bombardment, tritium decay and (n, α) reactions, which originate from the high flux of very energetic neutrons (14 MeV). High near-surface concentrations of implanted helium ions induce build-up blisters on the surface, or deform the surface in other ways. The first wall surfaces are also subject to high hydrogen ion and atom fluxes. Hydrogen and helium react synergistically on metal surfaces. The simultaneous reactions of helium and hydrogen under these conditions lead to interesting phenomena. The purpose of this work is to determine the effects of simultaneous helium implantation and hydrogen charging on the surface behavior of polycrystralline nickel. The severe hydrogen charging and high helium concentration develops damaged zones, and blister growth in these zones. A schematic description in the form of the "synergistic model" is suggested, which illustrates the formation of these blisters, and the effects of hydrogen charging on their development in pre-implanted metals. In this model, hydrogen recombines into its molecular state within the interbubble fracture, caused by the helium implantation. This increases the pressure of the trapped gas and induces blistering.