Three-dimensional imaging of shear bands in bulk metallic glass composites

The mechanism of the increase in ductility in bulk metallic glass matrix composites over monolithic bulk metallic glasses is to date little understood, primarily because the interplay between dislocations in the crystalline phase and shear bands in the glass could neither be imaged nor modelled in a validated way. To overcome this roadblock, we show that shear bands can be imaged in three dimensions by atom probe tomography from density variations in the reconstructed atomic density, which density-functional theory suggests being a local-work function effect. Imaging of near-interface shear bands in Ti48Zr20V12Cu5Be15 bulk metallic glass matrix composite permits measurement of their composition, thickness, branching and interactions with the dendrite interface. These results confirm that shear bands here nucleate from stress concentrations in the glass due to intense, localized plastic deformation in the dendrites rather than intrinsic structural inhomogeneities. Lay description Bulk metallic glass matrix composites combine the structure and properties of two different phases: a metallic glass phase and a crystalline phase, making them both strong and ductile. How can we better design these materials so they deform without breaking is the key question of this paper, which we address by imaging locally the regions where the material has deformed. Because of the complex arrangement of the two phases, we use an imaging technique (atom probe tomography) that provides 3D spatial information and we are able to reveal local deformation at the atomic scale, which we support and confirm using modelling.