Synthesis and Structural Properties of New Metallic Phases Exhibiting Non-Crystallographic Symmetries

摘要

In carrying out research on aluminum-glasses (Al-glasses), several unusualresults are found: (1) Submillimeter dutile glassy ribbons are obtained. (2) Significant enhancement in the tensile strength is measured in Al-glass ribbons with Al nanocrystallites embedded in them. (3) Deformation induced crystallization within the shear bands is observed for the first time. (4) Strong Al-transition metal interaction is inferred from x-ray and neutron diffraction measurements. These results have added to our understanding of formation and microstructure-mechanical effect relationships of metal glasses, and also to the technological values of these materials. We have begun to apply our findings to the synthesis and studies of bulk metallic-glass and nanocrystalline alloys. Thus far, we have succeeded in making subcentimeter glasses based on rare-earths and magnesium-tin, nanocrystalline alloys based on refractory metals via conventional casting, and as well as, centimeter Al-glass button via consolidation of amorphous powders obtained by ball-milling. In collaboration with Professor T. Egami at U. Penn., a method for obtaining two-dimensional atomic pair distribution is developed to unravel the structure of decagonal crystals. The new method will be applied to study layered materials. Submillimeter aluminum-glass ribbons, Subcentimeter, Glassy and nanocrystalline alloys, Mechanical properties, Structural studies, Decagonal crystals.