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Updated: May 30, 2026

Determining the Mechanical Strength of Ultra-Fine-Grained Metals
Published on: November 22, 2021
Absolute concentration of free volume-type defects in ultrafine-grained Fe prepared by high-pressure torsion
Bernd Oberdorfer1, Bernd Lorenzoni, Katrin Unger
1Institut für Materialphysik, Technische Universität Graz, Petersgasse 16, A-8010 Graz, Austria.
Abstract:
A maximum excess volume ΔV/V ≈ 1.9 × 10(-3) in ultrafine-grained Fe prepared by high-pressure torsion is determined by measurements of the irreversible length change upon annealing employing a high-resolution differential dilatometer. Since dislocations and equilibrium-type grain boundaries cannot fully account for the observed released excess volume, the present study yields evidence for a high concentration of free volume-type defects inherent to nanophase materials, which is considered to be the main source of their particular properties, such as strongly enhanced diffusivities.
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