Nanocrystallization During Nanoindentation of a Bulk Amorphous Metal Alloy at Room Temperature
J.-J. Kim,1
Y. Choi,1
S. Suresh,1
A. S. Argon2
It is known that nanocrystallites can form in shear
bands produced during severe bending or high-energy ball milling of
thin ribbons of a metallic glass. We present direct experimental
evidence that highly confined and controlled local contact at the
ultrafine scale in the form of quasi-static nanoindentation of a bulk
glassy metal alloy at room temperature can also cause
nanocrystallization. Atomic force microscopy and transmission electron
microscopy show that nanocrystallites nucleate in and around shear
bands produced near indents and that they are the same as crystallites
formed during annealing without deformation at 783 kelvin. Analogous to
results from recent experiments with glassy polymers, our results are
reasoned to be a consequence of flow dilatation inside the bands and of
the attendant, radically enhanced, atomic diffusional mobility inside
actively deforming shear bands.
1 Department of Materials Science and
Engineering,
2 Department of Mechanical Engineering,
Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
*To whom correspondence should be addressed. E-mail:
ssuresh{at}mit.edu
