Amorphous Silicates -- Time-Current Superposition and the Dynamics of Plastic Flow in the Glassy State

Abstract

Electron irradiation enables quantitative control over the plastic flow dynamics of silicate glasses, even far below the glass transition temperature. Through stress-relaxation experiments spanning ambient to near-glass-transition temperatures, we uncover a time-current equivalence that grants direct access to steady-state plastic flow over five decades in strain rate. This equivalence allows reconstruction of the intrinsic plastic-flow curve and quantitative assessment of the roles of network connectivity and temperature. Notably, the observed temperature dependence reveals a striking discrepancy with existing theoretical frameworks, highlighting the need for a comprehensive model of plastic flow dynamics in the glassy state.

Figures (3)

• Figure 1: a) Stress relaxation as a function of time measured at increasing electron current density (see panel c for legend), achieved by varying the SEM magnification and/or aperture. Relaxation accelerates systematically with increasing current density. b) Flow curves derived from the relaxation data in panel a). c) Master flow curve obtained by time-rescaling the partial flow curves shown in panel b). Inset: time-scaling factors as a function of current density, revealing an inverse relationship between current density and the characteristic timescale of plastic flow.
• Figure 2: Impact of temperature on the plastic flow of silica under electron irradiation: a) reference flow curves for various temperatures up to 873 K - stress has been normalized to temperature; b) time scaling factors as a function of current - the time scaling factors are independent of temperature; c) flow rule parameters $a$ and $b$as a function of temperature. The process seems largely athermal with little evolution of $a$ and $b$ below 500 K but but a significant decrease at higher temperatures.
• Figure 3: Impact of network depolymerization on the plastic flow of amorphous silicates under electron irradiation: a) master flow curves for SLS and ABS glasses; b) time scaling factors as a function of current density for SLS and ABS. As for silica, the relation is nearly inverse, but the exponents are slightly larger; c) SLS pillar morphologies after compression at constant strain rate under electron irradiation (left) and in the absence of irradiation (right). Shear bands are characteristic of the compression of ABS and SLS but are suppressed under irradiation.