Nanostructured crystalline and glassy materials: a new state of matter by extreme plastic shear deformation
Hans-Jörg Fecht
Institut für Mikro- und Nanomaterialien, Universität Ulm
17:15 - 18:15 Tuesday 06 May 2008 TUG Recent results on the fundamentals of plastic deformation of fully dense nanocrystalline materials and metallic glasses will be presented. The first model system investigated is Pd (fcc) and several single-phase Pd alloys. The experiments focus on mechanical tests using new testing equipment for miniaturized specimens with different stress state conditions. The aim is to obtain a significantly improved database of materials behaviour for these alloys at a grain size between 10 and 30 nm, since this has previously only been explored sporadically, and to elucidate and describe the microscopic mechanisms that mediate the deformation.
Furthermore, by the same method of high pressure torsion it becomes possible to change and tune the volume of a material considerably. This method can therefore used to (i) fully densify a collection of metallic glass nanoparticles and (ii) modify the atomic structure of a metallic glass by the formation of a high density of primary and secondary shear bands. Recent computer simulations show some of the mechanisms of the redistribution and increase in free volume when certain defects are injected. A maximum increase in volume up to about 10% can be expected before the formation of nanovoids occurs. This new state of matter, so-called nanoglass, exhibits properties much different from the conventional crystalline or glassy state in terms of its thermodynamic, mechanical, magnetic, transport properties etc. These changes are enormous when compared with conventional crystalline and nanocrystalline materials and open possibilities for the design of new materials.
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