Constitutive model for inhomogeneous flow in bulk metallic glasses
Alban Dubacha, Florian H. Dalla Torrea and Jörg F. Löfflera
aLaboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland
Received 3 July 2008; revised 20 October 2008; accepted 20 October 2008. Available online 27 November 2008.
Abstract
This study presents results on the mechanical properties of Zr-based bulk metallic glasses over a wide range of temperatures (77–673 K) and strain rates (3.3 × 10−5 − 0.2 s−1), and provides novel information on the kinetics of inhomogeneous deformation in metallic glasses. The disappearance of serrated flow, i.e. temporal homogenization, below a critical temperature and above a critical strain rate corresponds to a transition of the asymptotic strain rate sensitivity (SRS) from negative to positive values. Based on thermally activated shear processes a temperature and strain rate dependent deformation model is presented that includes a time-varying state variable which represents the local degree of relaxation in the shear band after a shear event has taken place. The model makes possible a theoretical description of the observed SRS and the spatio-temporal evolution of plastic deformation in metallic glasses.
Keywords: Bulk metallic glasses; Inhomogeneous deformation; Strain rate sensitivity; Deformation kinetics; Activation volume