Poly-glasses — A New Kind of Glasses with Microstructures Utilized in Crystalline Materials for more than 6000 Years
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Аннотация
Herbert Gleiter
Karlsruhe Institute of Technology (KIT), Germany
Most technological applications of crystalline materials are based on the modification of their microstructure (e.g. of their grain size and/or of the topology of different phases that may be present). It was this modification that marked the beginning of the metal age more than 6000 years ago and resulted in materials like polycrystalline Au, Cu, bronze, Fe-alloys and most of today’s materials.
In this presentation it is suggested that similar developments may be triggered today in the area of glasses by introducing (1) defects into glasses in the form of glass/glass interfaces. (Glasses with this microstructure will be called poly-glasses in analogy to poly-crystals). (2) By generating glasses consisting of regions with different chemical compositions, e.g. two chemically different metallic glasses. (Glasses of this kind will be called multi-phase poly-glasses).
Both kinds of poly-glasses were generated by the following two-step process. In the first step, small e.g. nanometer-sized glassy clusters — with identical chemical compositions — were produced (e.g. by inert gas condensation). These spheres were subsequently consolidated and sintered under high pressure and below the glass transition temperature (Tg) into a poly-glass. The resulting poly-glass was found to consist of glassy regions connected by glass/glass interfaces which differ in density and atomic structure from the adjacent glassy regions. In comparison to a melt-spun glass (with the same composition) poly-glasses were found to have new properties. For example, a ScFe (20at% Sc) poly-glass was (at 300 K) a strong ferromagnet, whereas the melt-spun form (same composition) was paramagnetic.
Another new aspect of poly-glasses is their microstructural stability. If they are annealed below Tg, the glass/glass interfaces delocalize so that the free volume that is initially localized in these interfaces, is smeared out laterally. An analogues process does not exist in poly-crystals.
The delocalization generates a new degree of freedom for modifying the structure and hence the property of poly-glasses.
Multi-phase poly-glasses were generated by high pressure sintering of mixtures of glassy clusters with different chemical compositions. The properties of these poly-glasses may be controlled by varying the chemical composition of the spheres, their size and/or their spatial arrangements as well as the degree of interfacial delocalization.
In addition to the poly-glasses discussed so far, the way to another family of poly-glasses may be opened by using mixtures of glassy as well as crystalline clusters.
