Prof. Jürgen Eckert

Abstract:

Recent studies of glass-forming metallic systems have revealed intriguing complexity, e.g. unusual shifts in radial distribution functions with temperature change or upon mechanical loading in the elastic or plastic regime. Nearest neighbour distances and medium-range order structural arrangements appear to change, e.g. shorten upon heating or become larger with decreasing temperature. Concomitantly, temperature changes as well as static or dynamic mechanical loading within the nominally elastic regime can trigger significant changes in glass properties, which are directly correlated with local non-reversible configurational changes due to non-affine elastic or anelastic displacements. All these findings strongly suggest that the characteristics of the atomic structure decisively determine the properties of the glass and of nanostructured materials derived from glass-forming systems.

Residual stress engineering is widely used in the design of new advanced lightweight materials. For metallic glasses the attention has been on structural changes and rejuvenation processes. High energy scanning x-ray diffraction strain mapping reveals large elastic fluctuations in metallic glasses after deformed under triaxial compression. Transmission electron microscopy proves that structural rejuvenation under room temperature deformation relates to the shear band formation that closely correlates to the underlying distribution of elastic heterogeneities. Micro-indentation hardness mapping hints at an unsymmetrical hardening/softening after compression and further reveals the competing effects of stress and structure modulation. Molecular dynamics simulations provide an atomistic understanding of the correlation between shear banding and fluctuations in the local strain/stress heterogeneity. Thus, stress engineering and elastic heterogeneity together with structure modulation is a promising approach for designing metallic glasses with enhanced ductility and strain hardening ability.