Toughness, extrinsic effects and Poisson's ratio of bulk metallic glasses

A range of bulk metallic glasses has been cast and their mode II fracture toughness has been estimated from the length scale of shear band vein patterns on fracture surfaces. As-cast rare-earth and Mg-based bulk metallic glasses invariably consist of oxide particles dispersed in a glassy matrix and the apparent brittleness of these alloys is partly extrinsic in nature, caused by these inclusions. The intrinsic toughness of these glasses is higher than previous reports suggest. An attempt has been made to correlate the toughness of a variety of glassy alloys, including La- and Mg-based systems, with their Poisson's ratio (nu). The findings show that mode II toughness increases with v, though gradually, instead of an abrupt transition occurring at a critical value of nu. Certain glassy alloys are profoundly brittle, irrespective of nu, and this seems to be related to alloy chemistry. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.