Dresden 2011 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 34: Nanomaterials I

MM 34.1: Talk

Thursday, March 17, 2011, 11:00–11:15, IFW B

Random structural inhomogeneities in the axial direction in high pressure torsion processed samples — •David Geist, Hans-Peter Karnthaler, and Christian Rentenberger — University of Vienna, Physics of Nanostructured Materials, Boltzmanngasse 5, 1090 Wien, Austria

High pressure torsion (HPT) is a widely used method of severe plastic deformation to produce bulk nanostructured materials. In this study, it is shown for the intermetallic compound Zr3Al by TEM and SEM methods that grain refinement happens in a random manner. This contradicts the commonly accepted HPT formula which predicts that grain refinement, prior to saturation, should have a radial dependence only. Unlike earlier findings of violations of the HPT formula, that showed systematic inhomogeneities along the axial direction due to material flow during the early stages of HPT deformation, this work presents a mostly random refinement behavior along both the radial and the axial direction. In this inhomogeneous structure, refined regions carry most of the deformation while coarse grained regions hardly get deformed. Local hardness measurements are able to explain this deformation behavior by revealing the refined structure being softer. To study in detail the interface regions between these structurally distinct sample volumes, some samples were surface treated prior to deformation, leading to a systematic localization of the refined regions at the sample surfaces. High resolution TEM of the interface region reveals twinned structures and high dislocation densities, that could arise by the large strain gradient present at the interfaces.