Multiple semi-coherent particles strengthened ultra-fine-grained Al composites for neutron shielding materials

Neutron shielding materials face imbalanced behaviors among shielding, strength, and ductility properties. Based on the requirement of the high property shielding particles, a superior semi-coherent τ(Al4MgGd) phase was designed and predicted by cluster expansion (CE) method using density functional theory calculations. To realize its shielding property, the Powder Metallurgy-based routines (i.e., powder fabrication, spark plasma sintering, and hot extrusion techniques) are used to fabricate 6TiB2/Al-6Mg-5Gd (wt.%) composite with dispersed refined τ phases and homogenized TiB2 distribution. The atomic structure of ternary phase τ is examined by aberration-corrected high-angle annual dark-field (HAADF) scanning transmission electron microscope (STEM) and energy dispersive X-ray spectroscopy (EDXS) STEM experiments, which is well complied with the calculated compound (Al4MgGd). In detail, the τ(Al4MgGd) phase has a semi-coherent interface both with α-Al and TiB2, which is consistent with the prediction of interface relationships. With the optimized interfaces, the TiB2 and τ phases can effectively promote recrystallization and suppress grain growth, leading to the formation of ultra-fine grain structure. Then, the composite exhibits advanced shielding properties (Macroscopic transmission cross section ∼24.1 /cm, higher than 30%B4C/Al) and optimized synergic mechanical properties (Ultimate tensile strength ∼506 MPa, elongation ∼12.9%), which are far higher than available Al-based neutron shielding materials. Finally, the underlying strength-ductility mechanisms are discussed. Critically, the design and optimization of shielding particle interfaces are reliable strategies for developing novel structural-functional integrated materials.