Structure, Properties and Relaxation of Shear Bands in Metallic Glasses

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TECHNICAL: Catastrophic failure at a single shear band has posed challenges to structural applications in metallic glasses. While much research effort is directed at preventing such a failure, the fundamental understanding of shear-band behavior is still incomplete. The goal of this work is to obtain a deeper understanding of the relationships between the structure and properties of shear bands, and the dependence of both on thermal relaxation. This goal will be achieved by a combination of targeted experiments and modeling. Shear bands will be formed under varying conditions, and their structure and thermal and mechanical properties will be characterized. Experimental techniques to be used include conventional and high-resolution transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, nanoindentation, spring-back measurements and conventional mechanical tests. Chemical disorder will be explored as a source of diffraction contrast in transmission electron microscopy. The use of a synchrotron x-ray nanoprobe for shear-band characterization will be explored. The high amount of free volume at shear bands offers an opportunity for studying the behavior of metallic glasses in a highly unrelaxed state. Experiments aimed at direct characterization of the local properties of shear bands will be performed. Deformation modes in samples containing shear bands will be explored for a range of strain rates. The high stability of bulk metallicglasses will allow an extensive study of the effect of relaxation on properties. One goal will be a determination, based on several properties of the extent to which the "memory" of shear bands can be erased by relaxation. Previous theoretical models will be applied and extended to analyze the results. NON-TECHNICAL: Metallic glasses have generated much scientific and technological interest due to their unique physical properties. Their high elastic limit and yield strength are attractive for structural applications, which have become a reality with the development of bulk synthesis. The broader impacts are scientific, technological and educational. The expected results will improve the fundamental understanding of the structure-property relationship in metallic glasses. They will contribute to the knowledge base for structural applications of metallic glasses. These studies will help educate and train graduate students. They will learn materials fundamentals, develop the ability to plan and conduct research, and will become proficient in state-of-the-art electron microscopy, x-ray diffraction and property characterization of structural materials. In addition, graduate students will learn to communicate their results to the scientific community orally and in writing