Some of the broader impacts of our work include...

1. Structural basis for fracture toughness of metallic glassesTodd Hufnagel, Johns Hopkins University, DMR 0705517 Metallic glasses are potentially promising structural materials, combining the outstanding mechanical properties of metals with the processing flexibility of glasses. However, metallic glasses can be quite brittle. We seek to understand how the atomic-scale structure influences the fracture behavior of these novel materials. Developing a detailed picture of the structure of disordered materials remains a significant challenge. We are addressing this by combining x-ray and neutron scattering (top figure) with fluctuation electron microscopy (FEM) and computational models. FEM provides information about higher-order (3- and 4-body) atomic correlations, but incorporating these data into the models required the development of new, computationally efficient techniques for calculating FEM signals (middle figure). Our results on Pd-Ni-P metallic glasses (bottom) indicate that variable coherence FEM data do not provide significant constraints on the models that are not already present in the x-ray and neutron scattering data. This suggests that the frequently invoked "medium range order" is a consequence of atomic packing constraints. Above: Comparison of resonant x-ray and neutron scattering data from a Pd-Ni-P metallic glasswith a Reverse Monte Carlo model. Left: Schematic of calculation of FEM signal from atomic model. Below: Illustration of four-body correlation plots from models generated with and without FEM constraints.

2. Structural basis for fracture toughness of metallic glassesTodd Hufnagel, Johns Hopkins University, DMR-0705517 Some of the broader impacts of our work include... Education: One Ph.D. thesis has been completed, by Dr. Stephan Hruszkewycz, who has gone on to a post-doctoral research position at Argonne National Laboratory. A second Ph.D. project (by Uday Vempati) is now underway. Additionally, four undergraduates have participated in the research (right), including two students doing senior design projects. Graduate student Uday Vempati (left) and undergraduate Christopher Serrano discuss a photomicrograph of a metallic glass tensile specimen. Dissemination of results: To date we have published two papers in peer-reviewed journals, with another two in preparation. We have also given seven talks or seminars on this work, five of which were invited.