Researchers at the California Institute of Technology and
the U.S. Department of Energy's (DOE) Lawrence Berkeley National
Laboratory have combined efforts to create a glass that is said to be
the strongest out of any known material.
Ritchie, study leader and a material scientist from the Lawrence Berkeley
National Laboratory, along with co-authors Marios Demetriou, Glenn Garrett,
Joseph Schramm, Maximilien Launey, Douglas Hofmann, and William Johnson of the
California Institute of Technology, have developed a glass that is tougher and stronger
materials have a non-crystalline, amorphous structure, which makes them strong
yet brittle. This type of structure allows cracks and strains to spread
throughout the material because the glass' amorphous structure cannot stop
crack propagation. To remedy this, the Lawrence Berkeley/California Tech team
designed what they called "DH3," which was a fabricated metallic
glass capable of preventing cracks from spreading through the use of a second
crystalline phase of the metal. While this method prevented the spread of
cracks, these researchers wanted to take this research to the next level and
make it stronger.
Lawrence Berkeley/California Tech team came together once again to develop this
new glass, which is a damage-tolerant metallic glass made of microalloys of
palladium, which has a high bulk-to-shear stiffness ratio. The difference
between this new
glass and DH3 is that their new creation also promotes extensive
plasticity "through the formation of multiple shear bands before the bands
turn into cracks."
results mark the first use of a new strategy for metallic glass fabrication and
we believe we can use it to make glass that will be even stronger and more
tough," said Ritchie. "Because of the high bulk-to-shear modulus
ratio of palladium-containing material, the energy needed to form shear bands
is much lower than the energy required to turn these shear bands into cracks.
The result is that glass undergoes extensive plasticity in response to stress,
allowing it to bend rather than crack."
added that it is important to make a metallic glass with at least five elements
in order to quench the material, which means to cool the material. The first
samples of the metallic glass consisted of microalloys of palladium with
phosphorous, germanium, silicon and
silver. This increases the thickness of the glass rods, but the size is limited
to its need to rapidly quench the liquid metals for its final structure. When
it comes time to quench the liquid metals, it doesn't know which crystal
structure to form, so it automatically forms an amorphous structure.
game now is to try and extend this approach of inducing extensive plasticity
prior to fracture to other metallic glasses through changes in
composition," said Ritchie. "The addition of the palladium provides
our amorphous material with an unusual capacity for extensive plastic shielding
ahead of an open crack. This promotes a fracture toughness comparable to those
of the toughest materials known. The rare combination of toughness and
strength, or damage tolerance, extends beyond the benchmark ranges established
by the toughest and strongest
study was published in Nature Materials.