Fundamental studies of deformation physics in amorphous metals

Amorphous metals, or metallic glasses, are a unique new class of structural materials with interesting deformation mechanisms. Our group uses both experiment and simulations to study fundamental aspects of deformation in these alloys. Experimentally, we make extensive use of nanoindentation, where sudden displacement bursts have been observed in the force-displacement curves upon loading. Each burst results from a strain localization underneath the indenter in an individual shear band.  By studying how the serrations in these curves vary with glass composition, loading rate, and temperature, we have elucidated information about the deformation physics behind the process of shear banding.  Using these techniques, we have studied transitions between heterogeneous and homogeneous deformation regimes as well as the stresses required to initiate a shear band at a stress concentration. With simulations, we have explored the atomistic origins of pressure sensitive flow in metallic glass, and are currently exploring the process of the shear band formation.

See also the review articles:
Mechanical Behavior of Amorphous Alloys in Acta Materialia
and
Nanoindentation studies of materials from Materials Today

a)b)

Shear bands around a cylindrical indentation penetrate to a depth of more than twice the contact radius. a) Image of shear bands from cylindrical indentation [C Su, L Anand: Acta Materialia 2006;54:179] b) Stress field under a Hertzian contact. Contours of maximum shear stress (τ') and pressure-modified shear stress (τ' - αp' with α = 0.12) are shown on the right and left, respectively. The pressure modification reduces the maximum stress and shifts it slightly deeper into the material.

Published Articles:

Strength, plasticity and brittleness of bulk metallic glasses under compression: statistical and geometric effects
WU WF, LI Y, Schuh CA; PHILOSOPHICAL MAGAZINE 88 (1):71-89 JAN 2008 (PDF)

Initiation of a shear band near a stress concentration in metallic glass
Packard CE, Schuh CA; ACTA MATERIALIA 55 (16): 5348-5358 SEP 2007 (PDF)

New regime of homogeneous flow in the deformation map of metallic glasses: elevated temperature nanoindentation experiments and mechanistic modeling
Schuh CA, Lund AC, Nieh TG; ACTA MATERIALIA 52 (20): 5879-5891 DEC 2004 (PDF)

The Mohr-Coulomb criterion from unit shear processes in metallic glass
Lund AC, Schuh CA; INTERMETALLICS 12 (10-11): 1159-1165 OCT-NOV 2004 (PDF)

A survey of instrumented indentation studies on metallic glasses
Schuh CA, Nieh TG; JOURNAL OF MATERIALS RESEARCH 19 (1): 46-57 JAN 2004 (PDF)

Yield surface of a simulated metallic glass
Lund AC, Schuh CA; ACTA MATERIALIA 51 (18): 5399-5411 OCT 2003 (PDF)

The transition from localized to homogeneous plasticity during nanoindentation of an amorphous metal
Schuh CA, Argon AS, Nieh TG, Wadsworth J; PHILOSOPHICAL MAGAZINE 83 (22): 2585-2597 AUG 2003 (PDF)

Atomistic basis for the plastic yield criterion of metallic glass
Schuh CA, Lund AC; NATURE MATERIALS 2 (7): 449-452 JUL 2003 (PDF)

A nanoindentation study of serrated flow in bulk metallic glasses
Schuh CA, Nieh TG; ACTA MATERIALIA 51 (1): 87-99 JAN 2003 (PDF)