Advanced Shape-memory Bulk Metallic Glass Composites

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Bulk metallic glass matrix composites (BMGCs) containing uniformly dispersed shape-memory crystals have a large potential for applications because they constitute advanced materials with high toughness and high strength. Within the proposed project, we will tackle some of the most important unresolved issues related to the optimization of composite microstructures and the resulting mechanical properties of shape-memory BMGCs. In doing so, the suggested work focuses on preparing and characterizing different CuZr-based glass-forming alloys. Our approach consists of a systematic combination of various state-of-the-art experimental techniques (e.g. in-situ deformation in a HRTEM, in-situ deformation in a high-energy X-ray beam) complemented by finite element modelling, which will allow us to answer three fundamental questions: (1) What is the influence of the chemical composition and the fabrication process on the nucleation and growth process of the shape-memory crystals (i.e. the thermodynamic, kinetic and structural aspects related to the formation of the B2 CuZr phase) and thus on the microstructure formation? (2) What is the contribution of the glassy phase, the crystalline phase and the crystal-glass interface (mismatch strains at the interface) to the overall deformation mechanism? (3) How does the deformation-induced martensitic transformation in the crystals affect the overall plastic deformation in terms of the shear-banding process in the glass and how does the crystal-glass interface, in turn, modify the martensitic transformation in the crystals? The physical mechanisms underlying irreversible deformation, especially the toughening mechanisms, associated with the transformation-induced plasticity in the crystals will be elucidated. The successful implementation of the project is expected to lead to a significant advance in the understanding of the deformation mechanisms in shape-memory BMGCs. As an additional result, we will develop guidelines how to design and therefore optimize novel, strong and ductile BMGCs with advanced properties, which bring practical engineering applications within reach.