Abstract
We have developed a novel type of nanoindentation creep experiment, called broadband nanoindentation creep (BNC), and used it to characterize the thermal activation of shear transformation zones (STZs) in three BMGs in the Zr-Cu-Al system. Using BNC, material hardness can be determined across a wide range of strain rates (10
–4 to 10 s
–1) in a single experiment at room temperature. This data can be used to characterize the kinetics of deformation, including the free energy function (ΔG) for thermally-activated deformation. We have found that the activation energy agrees with the theory of Johnson and Samwer, in which ΔG ∝ [(τ
c – τ)/τ
c]
3/2, where τ is the flow stress and τ
c is the flow stress at 0K. In the context of their model, we estimate that the volume of an STZ is ~ 100-300 atomic volumes and the activation energies for low-stress deformation are 5-10 eV. From these measurements, it is possible to reproduce the temperature dependence of the flow stress.
Keywords
Metallic glasses,
materials,
creep,
testing,
strains,
stresses,
deformations,
nanotechnology,
nanostructured materials,
measurement,
zirconium,
copper,
aluminum,
hardness,
shear,
temperature,
elasticity,
broadband nanoindentation creep,
BNC,
creep,
kinetics,
nanoindentation
Citation
Puthoff, J.B.; Cao, H.B.; Jakes, Joseph E.; Voyles, P.M.; Stone, D.S. 2009. Shear transformation zone activation during deformation in bulk metallic glasses characterized using a new indentation creep technique. Local structure and dynamics in amorphous systems [electronic resource]. Materials Research Society symposium proceedings ; v. 1152. Warrendale, Pa. : Materials Research Society, [2009] :[6] pages. ISBN: 9781605111247:1605111244
