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MM: Fachverband Metall- und Materialphysik

MM 28: Nanostructured Materials I

MM 28.3: Vortrag

Mittwoch, 24. März 2010, 10:45–11:00, H16

Absolute concentration of free volumes in nanophase metals prepared by high-pressure torsion — •Bernd Oberdorfer¹, Wolfgang Sprengel¹, Daria Setman², Michael Zehetbauer², Reinhard Pippan³, Werner Puff¹, and Roland Würschum¹ — ¹Inst. f. Materialphys., TU Graz, 8010 Graz, Austria — ²Phys. Nanostrukt. Mater., Fakultät f. Physik, Univ. Wien, Austria — ³Erich Schmid Institute of Materials Science., Leoben, Austria

This contribution is concerned with the yet unsettled question of absolute concentrations of free volumes in nanocrystalline metals. Despite indications for high concentrations of lattice vacancies and excess volumes in non-equilibrated grain boundaries in these materials, studies by direct and specific methods are scarce. Initial studies to determine the absolute concentration of defects in nanocrystalline metals by time-dependent dilatometry are presented. Bulk nanocrystalline Cu and Fe samples were prepared by high pressure torsion. Length-change measurements with a differential dilatometer show the irreversible annealing of excess free volume Δ V/V of up to ca. 3×10⁻³ (Fe) or 1×10⁻³ (Cu) upon heating. The annealing behaviour is analyzed by non-isothermal transformation kinetics. The relative contributions of the various types of defects (vacancy agglomerates, dislocations, grain boundaries) with respect to the total excess free volumes are discussed. The dilatometric measurements are compared with studies of positron lifetime spectroscopy and differential scanning calorimetry. Financial support by the FWF Austrian Science Fund is appreciated (project P21009-N20).