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Tunable Tensile Ductility in Metallic Glasses


Metallic glasses
(MGs) are an exciting class of materials due to a suite of attractive
properties including high strength, large stretchability, high wear and corrosion resistance,
and excellent magnetic properties. However, adoption of MG in many applications
has been hindered by the fact that they are brittle: they can break apart very
suddenly, especially when put under tension. Ductility – the ability to softly
stretch without breaking – would be a better property to have.

A possible way to
make MG more ductile is to use extremely small specimen sizes. Typically, such
sub-micron specimens are produced using the focused ion beam (FIB) method.
However, in this process, unwanted ions can be implanted into the material, and
this may affect its behavior. We employed a novel nano-molding process to
produce pristine MG nanowires without using FIB. Thus, their properties are
unaffected by ion irradiation. We then performed tensile testing inside of a
scanning electron microscope to investigate whether subsequent exposure to ions
has an effect on the mechanical properties. The nanowires fail due in a brittle
manner when pulled in tension, as expected. After irradiation in the FIB, a
different glassy structure produced in the MGs, and the MG is significantly
less brittle.  Surprisingly, this
behavior can be reversed by then mildly heating the MG, thereby returning the
glass to its as-molded state. This shows that we can tune the ductility of MGs.

Representative stress-strain measurements, and the fracture morphologies for the

stress-strain measurements, and the fracture morphologies for the original, ion
irradiated, and irradiated and heated nanowires of MGs. The as-molded wires are
seen to fracture in a brittle manner, while the irradiated wires demonstrate tensile
ductility. Subsequently heating the nanowires brings back the brittleness.