Evolution of helium bubbles in nickel-based alloy by post-implantation annealing*

Abstract

Nickel-based alloys have been considered as candidate structural materials used in generation IV nuclear reactors serving at high temperatures. In the present study, alloy 617 was irradiated with 180-keV helium ions to a fluence of 3.6 × 1017 ions/cm2 at room temperature. Throughout the cross-section transmission electron microscopy (TEM) image, numerous over-pressurized helium bubbles in spherical shape are observed with the actual concentration profile a little deeper than the SRIM predicted result. Post-implantation annealing was conducted at 700 °C for 2 h to investigate the bubble evolution. The long-range migration of helium bubbles occurred during the annealing process, which makes the bubbles of the peak region transform into a faceted shape as well. Then the coarsening mechanism of helium bubbles at different depths is discussed and related to the migration and coalescence (MC) mechanism. With the diffusion of nickel atoms slowed down by the alloy elements, the migration and coalescence of bubbles are suppressed in alloy 617, leading to a better helium irradiation resistance.

Evolution of helium bubbles in FeCoNiCr-based high-entropy alloys containing γ′ nanoprecipitates

“…7 are approximately equal at 1-at.% and 3-at.% helium concentrations, which may be due to the fact that helium atoms reach a saturation concentration. [29,34] It is worth noting that the TEM observation sample of HEA-16 in Fig. 7 is prepared by the focused ion beam (FIB) method, which has a relatively uniform thickness of 100 nm.…”

Helium bubble formation and evolution in NiMo-Y2O3 alloy under He ion irradiation

“…[4] Because of their excellent resistance to high-temperature molten salt corrosion, nickelbased alloys have been widely developed to meet the service conditions of MSRs. [5] The Oak Ridge National Laboratory, USA, developed a nickel-based Hastelloy N alloy for applications in MSRs, which was considered to be the first option for structural metallic components in MSR due to its excellent chemical compatibility with fluoride molten salts. [6] However, severe helium embrittlement occurs in the Hastelloy N alloy under high neutron irradiation doses.…”