Ideal elastic, anelastic and viscoelastic deformation of a metallic glass

Abstract

The elastic, viscoelastic and anelastic components of the homogeneous strain response of the metallic glass Pd₈₂Si₁₈ to an applied stress have been examined. The elastic response is fully reversible, instantaneous and linear. The measured elastic modulus, E, and temperature dependence, d(ln E)/dT, are 84±8 GPa and (−3.2±0.6) × 10⁻⁴ C⁻¹, respectively. The viscoelastic flow is non-recoverable and, if the configuration remains constant, is characterized by a constant strain rate. This strain rate varies linearly with the stress, gtr, in the low stress regime (τ < 300 MPa), becoming non-linear for higher stresses. For isoconfigurational flow, the strain rate has an Arrhenius-type temperature dependence with an activation energy of - 200 ± 15 kJ mol⁻¹, independent of stress and thermal history. The magnitude of the strain rate is strongly dependent on the degree of structural relaxation and therefore on thermal history. During isothermal annealing the viscoelastic strain rate varies inversely with time. The anelastic response is a transient that, at 500 K, contributes to the flow for approximately fifty hours after a stress increase and is fully recovered upon stress reduction. A spectrum of exponential decays is required to model this flow component. The anelastic strain, τ _A, varies linearly with the magnitude of the stress change, Δτ, over the entire stress range tested: γ _A/gDAτ=(8.0±0.8)× 10⁻⁶ MPa⁻¹.