Atomistic investigation on radiation-induced segregation in W-Re alloy under cumulative flux irradiation: A hybrid simulation with MD and VC-SGC-MC

Due to its great performance, tungsten (W) and W-based alloys have been considered as the candidates for plasma-faced materials in future fusion reactors. However, the radiation-induced segregation under the reactor environment is one of the key issues to limit the long-term service properties of W-based alloys, and the un-derstanding of nucleation and growth mechanisms of Re-rich precipitates is still incomplete. In the present study, both molecular dynamics (MD) and variance-constrained semi-grand canonical ensemble Monte Carlo (VC-SGC-MC) methods are employed to investigate the nucleation and growth mechanisms of Re clusters precipitated in W-Re alloys under cumulative flux irradiation. It is found that all segregated Re-rich clusters in the model alloys without irradiation are a plate-like structure (chi-phase) which orientates along the < 110 >, while they change to a needle-like structure (sigma-phase) orienting along the < 111 > direction after irradiation. The combination of defects and Re atoms in W-Re alloys are considered with the most probable nucleation precursors. The Re-rich clusters will pin the interstitials and form stable nucleation sites. During the process of cumulative flux irradiation, newborn defects will be trapped by the nucleation site promoting the growth of Re clusters.