Suppression of repetitive surface exfoliation of Inconel 625 implanted sequentially with helium ions of different energies (20-100 keV)

Studies were conducted to explore if the surface exfoliation of Inconel 625, typical for 100 keV 4He+ irradiations can be reduced by pre-irradiating the surfaces with helium ions sequentially over the energy range 20 to 50 keV. Polished, polycrystalline Inconel 625 samples were irradiated at 298 K and 573 K with 4He+ at six different energies in the range from 20 to 50 keV in an order of decreasing energies. For each energy the dose was 0.13 C/cm2, resulting in a total dose of 0.89 C/cm2. Subsequently, these samples were implanted with 100 keV 4He+ to a dose of 1.0 C/cm2 or 2.0 C/cm2. The results reveal that the low energy 4He+ implants prior to the 100 keV 4He+ implant reduce significantly the erosion yield typical for 100-keV 4He+ irradiations alone. For 573 K these reduced yields are still about one order of magnitude greater than physical sputtering yields. (orig.)