Tailoring Deformation Characteristics of Bulk Metallic Glass Composites

Metallic materials with tailored properties are crucially important for a variety of structural and functional applications. There is a strong need not only for successful development of new high- performance alloys but also for elaborating suitable processing routes and characterization techniques enabling phase and microstructure selection and control, necessary for optimization of the related physical and mechanical properties. This talk explores the structural diversity and characteristic structure features of bulk metallic glasses and composites systems elucidating the role of tailored phase formation and microstructure design for deriving a detailed insight into deformation mechanisms and structure-property correlations of bulk metallic glass composites. In general, metallic glasses as characteristic disordered solids without long-range translational periodicity but distinct short- and medium-range order are materials with outstanding strength and elastic properties that make them tantalizing for engineering applications. Yet the poor understanding of how their amorphous atomic arrangements control their broader mechanical properties (hardness, wear, fracture, etc.) impedes the ability to apply materials science principles in their design. Hence, uncovering the hierarchical structure that exists in metallic glasses across the nano- to microscale is of utmost importance. The improved deformation behavior of bulk metallic glass composites (BMGCs) compared to monolithic bulk glasses render these materials interesting for possible applications, since these materials can circumvent the otherwise limited ductility or the even often catastrophic failure of monolithic bulk metallic glasses. However, the details of the deformation mechanisms in such composites are still not fully clear. Here, we report on BMGCs containing metastable β-Ti dendrites, crystals with dislocation-mediated plasticity or shape memory crystals, revealing that the overall deformation behavior can be significantly altered by the deformation characteristics of the crystals and/or by cooperative shear events of shear bands in the glassy matrix and strain-induced ω-Ti bands in β-Ti dendrites. If the crystals deform via dislocations, the shear bands are narrow and getting mature. In comparison, the shear bands in shape memory BMGCs continuously broaden by following thick martensitic plates without maturing, and broad shear bands bifurcate, inducing the formation of more martensitic variants and promoting strain delocalization. The broadening and bifurcation cause shear band blunting, accounting for the superior plasticity and work-hardening capability of shape memory BMGCs. Altogether, these examples show how advanced materials design combined with detailed structure characterization techniques allows deep insights into the atomic structure and the underlying mechanisms determining physical and mechanical properties, thus providing guidelines for optimized alloy design and tailoring of properties.