Lecturer: Prof. Michael Atzmon
Affiliation: Department of Nuclear Engineering
and Radiological Sciences,
Department of Materials Science and Engineering
The University of Michigan
Abstract:
Metallic glasses exhibit high strength and
elastic limit, making them attractive
candidates for structural applications.
However, they pose a significant
challenge as they also exhibit work
softening, which results in strain
localization and macroscopic brittle
behavior. Unlike for crystalline materials,
the defects that accommodate plasticity in
metallic glasses are not well understood,
and there is no known mechanism of
imaging them. In order to explore the
deformation mechanisms, we performed
quasi-static anelastic relaxation
measurements for a metallic glass over
nearly eight orders of magnitude of time.
Relaxation-time spectra computed from
the data revealed an atomically quantized
hierarchy of shear transformation zones,
and yielded their size-density distribution.
This distribution agrees with a model we
propose, based on free-volume statistics.
A similar approach allowed us to obtain
consistent temperature-dependent results
from dynamic-mechanical data. Analysis
based on our experimental results yields
two major conclusions: 1) primary (α) and
secondary (β) relaxations in non-
molecular glasses originate from the same
mechanisms; 2) the temperature-time
superposition method can erroneously
yield a single activation energy.