Molecular dynamics study of the role of anisotropy in radiation-driven embrittlement

Abstract

This study investigates the influence of crystallographic orientation on fracture behavior and the resulting mechanical anisotropy in a Fe55Ni19Cr26 alloy crystal containing radiation-induced defects, using molecular dynamics (MD) simulations. Crack propagation is analyzed in irradiated samples with three selected high-symmetry crystallographic orientations to show how radiation-induced defects modify local deformation mechanisms and amplify mechanical anisotropy. The investigation focuses on the anisotropic nature of the ductile-to-brittle transition (DBT) driven by radiation-induced defects by simulating fracture behavior under tensile loading. Fracture resistance is quantitatively evaluated using a traction-separation (T-S) approach to extract the atomic-scale fracture energy under realistic defect conditions. The results reveal a strong crystallographic orientation dependence in the evolution of deformation and fracture behavior during DBT. The crystal lattice orientation governs dislocation activity and defect interactions, which in turn regulate local plasticity mechanisms, strain localization, slip system activation, and fracture resistance, thereby driving the development and enhancement of mechanical anisotropy in irradiated materials. It is further shown that radiation-induced embrittlement cannot be explained solely by defect accumulation, but rather by orientation-sensitive interactions among dislocations, defects, and fracture process zones. A key novelty of this work lies in integrating radiation-induced defect evolution with orientation-dependent fracture within an atomistic T-S analysis, enabling quantitative assessment of atomic-scale fracture resistance under realistic defect conditions.

Figures (23)

• Figure 1: Fe$_{55}$Ni$_{19}$Cr$_{26}$ samples irradiated using sequential collision cascades at three damage levels (0.008, 0.038, and 0.152 dpa) for the crystallographic orientations (001), (011), and (111). The legend indicates the types of dislocation loops. Voids are marked as blue spheres.
• Figure 2: Evolution of dislocation density as functions of irradiation dose (dpa) for the (001), (011) and (111) orientations.
• Figure 3: Evolution of void number density (left) and cumulative void volume distribution (right) as functions of irradiation dose for the (001), (011), and (111) orientations.
• Figure 4: Populations of radiation-induced voids at dpa = 0.152 for selected orientations.
• Figure 5: Three-dimensional MD model for simulating fracture under tensile loading with a pre-crack, showing the $x$--$y$ projection on the left, and $y$--$z$ projection on the right for (001) orientation; five colored boxes indicate subvolumes used to model the material's resistance to crack propagation.