Sub-nanometer open volume regions in a bulk metallic glass investigated by positron annihilation

The size distribution of open volume regions in a Zr-based bulk metallic glass is investigated by positron annihilation lifetime spectroscopy. Three lifetime components are identified, indicating the presence of three distinct size ranges for open volume defects in the glass. The first two components compare favorably with literature values for bulk and vacancy annihilation in crystalline Zr, and are assigned to annihilation in the densely packed bulk and loosely packed flow defects within the glass. The third lifetime component corresponds to the annihilation of ortho-Positronium in a very low concentration of voids with radii 2.1-2.7 angstrom. The sizes of all three defects decrease with inhomogeneous deformation, while the concentrations of flow defects and voids increase. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.