Shear transformation zone dynamics model for metallic glasses incorporating free volume as a state variable

Abstract

A meso--scale model, shear transformation zone dynamics (STZ dynamics), is employed to investigate the connections between structure and deformation of metallic glasses. The present STZ dynamics model is adapted to incorporate a structure--related state variable, and evolves via two competing processes: STZ activation that creates free volume vs. diffusive rearrangement that annihilates it. The dynamical competition between these two processes gives rise to an equilibrium excess free volume that can be connected to flow viscosity via the phenomenological Vogel--Fulcher--Tammann relation in relaxed structures near the glass transformation temperature. On the other hand, the excess free volume allows glasses to deform at low temperatures via shear localization into shear bands, even in presence of internal stress distributions that arise upon cooling after processing.

On the Modelling of the Transient Flow Behavior of Metallic Glasses: Analogy with Portevin-Le Chatelier Effect

“…Almost of the adjustable model parameters obtained are physically meaningful and comparable with those found in the literature. Q STZ , V a and E are close to that obtained in references [5,27,29,30]. The value of γ 0 , ν 0 , α 0 is in agreement with similar published results [32].…”

Cryogenic-temperature-induced transition from shear to dilatational failure in metallic glasses

“…Mechanical failure of metallic glasses continues to fascinate researchers [1][2][3][4][5], since dislocations, grain boundaries, crystallographic planes, etc., are not defined in this class of non-crystalline materials [6][7][8][9]. Instead, the shear transformation zone (STZ), i.e.…”

Midinfrared Absorption Measurements of Nitrous Oxide in Ammonium Dinitramide Monopropellant Thruster

“…γ 0 ∼ 0.1 is the unit strain at which STZs transform on average [22,34,46]. The above considerations yield a reasonable characteristic shear rate on the order of 10 10 −10 12 s −1 , which is commonly assumed in the literature [22,34,50]. Our MD predictsγ 0 = 1.2 × 10 10 s…”