Topic: High Strength and Ductile Bulk Metallic Glasses and Nanostructured Composites

Metallic glasses and nanostructured materials are well-known to have attractive mechanical properties that are often superior to the performance of conventional coarse-grained crystalline materials. As a result these metastable materials are attractive candidates for a variety of structural and functional applications. However, one major drawback that still limits such applications is the pronounced tendency of amorphous and nanostructured materials for shear localization, especially upon room temperature deformation under unconstrained conditions. Accordingly, finding ways to improve their plastic deformability and toughening behavior are an urgent task for further materials development.

To circumvent such limitations, over the last years concepts of creating heterogeneous materials with nanostructured or glassy matrix and different type and length-scale of second phases have been followed to control the mechanical properties by proper alloy and microstructure design. The recent developments along this line will be summarized and new results for different types of alloys in Ti-, Zr- and Cu-base systems will be presented to illustrate how the mechanical properties can be tuned by appropriate phase and microstructure control. This will cover selected examples for glassy/nanostructured alloys with ductile primary precipitates, simple nanoscale eutectic structures as well as bulk metallic glasses with ultrafine-scale structural inhomogeneities. In all these cases the details of the metastable phase formation are closely linked with optimized processing conditions required to form the desired microstructure. The possible mechanisms that govern the deformation behavior will be critically assessed and the microscopic processes will be linked with the overall plastic deformation and fracture of the material.

Special emphasis will be placed on the link between quenched-in structural inhomogeneities on different length-scale, localized changes in topological and chemical short-range order, dynamic nanocrystallization and mechanically-induced phase transitions and their impact on improving the macroscopic plasticity of the material and inducing work hardening. Along this line a correlation between the macroscopic deformation and fracture with the underlying mechanisms on the atomic scale will be proposed, that attempts to link the local stress-strain conditions with local variations in elastic properties.

Curriculuum Vitae -- JuergenEckert