M. Schaenen; J. Li; Q. Tang; M. Hassani
Ceramics International 51 (2025) 59811-59819
Glass offers high strength and finite plasticity owing to its well-known amorphous structure. While the plastic
behavior of glass has been extensively studied using Cooperative Shearing Model (CSM) theory, the effect of free
volume on the shear transformation zone (STZ) and strain rate sensitivity (SRS) remains elusive. Here, we
performed nanoindentation tests at strain rates ranging from 0.01 to 1 s-1 to investigate the change in STZ
parameters and SRS as a function of the reduction of free volume in a chemically strengthened/ion exchanged
(IOX) glass and its as-received counterpart. Our results reveal that the IOX glass exhibits a larger STZ volume,
activation energy, and barrier energy density, leading to a lower SRS than the as-received sample. Additionally,
as the strain rate increases, the STZ volume and activation energy decreases while the shear strength increases
due to the insufficient free volume in the STZ. We further discussed the physical origin of the SRS as a function of
the ratio of the change in STZ free volume over the change in total STZ volume.