Crack Propagation and Shear Band Evolution in Marginal AL-RE Metallic Glasses

Abstract

Aluminum-rare earth marginal metallic glasses (MMGs) exhibit unique devitrification behavior, with an exceptionally high density of face-centered cubic (fcc) Al nanocrystals after the first crystallization reaction. The origin of these highly populated fcc-Al nanocrystals has been linked to a possible medium-range order (MRO) that exists within the as-quenched MMGs. However, the formation and propagation of shear bands in these MRO containing marginally glassy metallic alloys have not been thoroughly investigated and remain an open question. In this respect, we have investigated the shear band propagation using in-situ tensile straining within a transmission electron microscope (TEM). The results reveal that deformation-induced nanocrystallization occurs within shear bands, with fcc-Al nanocrystals forming in the adiabatic heat-affected zone as the crack propagates. TEM analysis indicates that nanocrystals with an average size of 5 nm form at shear bands before final fracture, providing enhanced crack deflection and energy dissipation. In that sense, MRO within the amorphous structure is believed to act as precursors, enabling the rapid formation of these fcc-Al nanocrystals under mechanical loading. Additionally, it has been shown that MRO causes heterogeneous mechanical responses, leading to variations in shear resistance within the glassy matrix. These variations contribute to the redirection, branching, and blunting as they encounter MRO embedded regions with differing local stiffness and energy dissipation capacity. © 2025 Elsevier B.V., All rights reserved.Aluminum-rare earth marginal metallic glasses (MMGs) exhibit unique devitrification behavior, with an exceptionally high density of face-centered cubic (fcc) Al nanocrystals after the first crystallization reaction. The origin of these highly populated fcc-Al nanocrystals has been linked to a possible medium-range order (MRO) that exists within the as-quenched MMGs. However, the formation and propagation of shear bands in these MRO containing marginally glassy metallic alloys have not been thoroughly investigated and remain an open question. In this respect, we have investigated the shear band propagation using in-situ tensile straining within a transmission electron microscope (TEM). The results reveal that deformation-induced nanocrystallization occurs within shear bands, with fcc-Al nanocrystals forming in the adiabatic heat-affected zone as the crack propagates. TEM analysis indicates that nanocrystals with an average size of 5 nm form at shear bands before final fracture, providing enhanced crack deflection and energy dissipation. In that sense, MRO within the amorphous structure is believed to act as precursors, enabling the rapid formation of these fcc-Al nanocrystals under mechanical loading. Additionally, it has been shown that MRO causes heterogeneous mechanical responses, leading to variations in shear resistance within the glassy matrix. These variations contribute to the redirection, branching, and blunting as they encounter MRO embedded regions with differing local stiffness and energy dissipation capacity.