Papers by Author: Harald Rösner

Abstract: In this study we show that in-situ tensile tests performed in a transmission electron microscope (TEM) in combination with high-resolution TEM are feasible, and, that this method is appropriate to elucidate the deformation processes in nanocrystalline materials directly. First results on nanocrystalline Pd produced by repeated cold-rolling with intermediate folding of metal sheets are presented revealing that the material ruptured during the in-situ tensile tests along grain boundaries. Deformation twinning was observed in grains next to the crack indicating that the deformation processes must have originated from the grain boundaries.

Abstract: Deformation-induced nanocrystallization has been investigated in a marginally Al88Y7Fe5 glass forming alloy. Conventional calorimetry and microstructural analyses of materials that have been subjected to high pressure torsion straining (HPT) at room temperature indicate the development of an extremely high number density of small Al nanocrystals. The nanocrystals appear to be distributed homogeneously throughout the sample without any evidence of strong coarsening. Moreover, the comparison between nanocrystallization caused by the application of either HPT, cold-rolling or in-situ TEM tensile straining yielded the identification of the probable mechanisms underlying the formation of nanocrystals. These results form the basis for the development of advanced processing strategies for producing new nanostructures with high nanocrystal number densities which allow increased stability and improved performance.

Abstract: New opportunities for fabricating massive nanocrystalline materials in bulk quantities are required for facilitating the transition of nanocrystalline solids from laboratory samples to technologically relevant materials. Advanced options might be based on combining different nonequilibrium processing routes sequentially, such that an initially metastable state is continuously energized and successively driven farer away from thermodynamic equilibrium. The current paper presents recent results on the evolution of nanoscaled microstructures resulting from combinations of different plastic deformation treatments or of vitrification and severe plastic deformation.