Activation volume details from nonlinear anelastic deformation of a metallic glass

Abstract

At high stress, the viscosity of a metallic glass is non-Newtonian, and therefore the rate of anelastic stress relaxation is not linear in the applied stress. In this regime, one can obtain information on the details of the activation volume that are not accessible in the linear regime. While bending in the nonlinear regime introduces a complicated stress state, it offers great stability for noninstrumented measurements over many orders of magnitude of time. We have developed a method of controlled sample bending to a strain of up to ∼0.0155 for Al86.8Ni3.7Y9.5 metallic glass. Significant nonlinearity of the anelastic strain in the stress was observed, which is mainly associated with the largest and slowest shear transformation zones involved not reaching mechanical equilibrium at the end of the constraining period. Combining nonlinear kinetics under constraint and zero bending moment after constraint removal, the volume of the largest shear transformation zones and the transformation shear strain were obtained independently for the inherent state—their most likely values are 4.8 × 10−28 m3 and 0.18, respectively.