Irradiation-induced defect evolution and mechanical behavior of gradient nanocrystalline Fe-9Cr alloy

Reduced-activation steels are key candidate structural materials for fusion reactor blankets, but neutron irradiation can degrade their mechanical properties. In this study, molecular dynamics simulations were employed to investigate irradiation-induced damage evolution and post-irradiation tensile behavior in gradient nanocrystalline Fe-9Cr alloys subjected to a single 100 keV Fe PKA event. As the gradient coefficient (g) increased to 1.2, both the peak defect yield and stable residual defects decreased, indicating that, under the present simulation conditions, a moderate structural gradient can suppress peak defect production and promote defect recovery. At g = 1.2, the model exhibited Δ σ Max and Δ σ f values of only 0.86% and −0.77%, respectively, together with the smallest variations in the plasticity parameter α and toughness U, demonstrating excellent irradiation-resistant mechanical stability. This behavior is attributed to the more continuous grain-boundary-mediated deformation at this gradient level, which facilitates a more homogeneous distribution of shear strain and more coordinated dislocation motion.