Fabrication of equiaxed ultrafine-grained structures in TiB₂/Al-Mg-Gd neutron shielding composites by powder metallurgy routines

Ultrafine-grained structures have increasingly contributed to the improvement of neutron shielding property and mechanical property of neutron shielding structural materials. Based on the powder metallurgy routines (i.e, powder fabrication, spark plasma sintering and hot extrusion techniques) and the presence of multi-scaled particles, the equiaxed ultrafine-grained structures were obtained in in-situ TiB₂/Al-Mg-Gd neutron shielding composites in this work. The as-sintered composites were prepared at either 405 °C or 480 °C, and both of them exhibited equiaxed fine grain structure. Specifically, the grains and τ phases were smaller in the composite sintering at lower temperature. Then, this composite was hot extruded, and found to show a larger number of equiaxed ultrafine grains (73.7%) and high angle grain boundaries (86.5%). Herein, the related grain refining mechanisms were discussed on dynamic recrystallization behaviors using electron backscattered diffraction and transmission electron microscopy analyses. In detail, the equiaxed ultra-fine grains were formed either by “pinching off” process from geometric dynamic recrystallization or progressive lattice rotation from continuous dynamic recrystallization. Critically, the effects of multi-scaled particles on the dynamic recrystallization were analyzed by accelerating misorientation accumulation and suppressing dynamic grain growth. Therefore, the ultrafine-grained composite had the improved strength and equivalent plastic deformation ability, which should shed light on the development on the structural-functional integrated materials. © 2023 Elsevier Inc.