Microstructure evolution in multi-principal element alloy with millimeter-sized grains subjected to cyclic torsion

In the previous report [ Acta Materialia 275 (2024) 120,059], the dislocation patterns and evolution process of fine-grained Al _0.1CoCrFeNi multi-principal element alloy with an average grain size of 46 μm were investigated at varying cumulative plastic strains, γ _cu, by double-beam TEM observations. To further understand larger grain size effect, the mechanism of intrinsic dislocation activities in the same alloy with millimeter-sized grains at the same loading conditions was studied in this paper. Different from the extensive proliferation of multi-slip dislocation activities and the resultant randomly distributed Lomer-Cottrell (L-C) locks and cells in the fine-grained alloy, multiple dislocation slip containing less slip-systems and parallel ordered L-C locks are preferentially activated, consequently promoting the generation of profuse geometrically necessary boundaries (GNBs) in the interior of millimeter-sized grains. With further increasing γ _cu, the GNBs progressively increases in the density and decrease in spacing, which also accelerates the formation of ultrafine-scale dislocation cell pattern.