Room-temperature Flow At Shear Bands In A Metallic Glass Michael Atzmon, University of Michigan Ann Arbor, DMR 0605911. Graduate students: Adam Ganuza, Jong Doo Ju.
In A Metallic Glass
Michael Atzmon, University of Michigan Ann Arbor, DMR 0605911
Graduate students: Adam Ganuza, Jong Doo Ju
Background: Our earlier nanoindentation studies in Al86.8Ni3.7Y9.5suggested a possibility of room-temperature viscous flow at pre-existing shear bands, created by cold work. In order to further study this behavior, shear bands were created in a ribbon sample. The evolution of the associated surface offset under applied stress was studied ex situ by atomic force microscopy (AFM).
Low-rate indentation of a rolled sample results in deformation at pre-existing shear bands. No new shear bands are formed.
a) Significant flow is observed at shear bands at room temperature in this metallic glass which has a glass transition temperature near 280 °C.
b) The offset decreases, even though the applied stress is expected to drive an increase.
c) This trend is likely due to residual stress created when the shear bands are formed by creating a kink. The residual stress is greater than the applied stress. Speculation: the effect of applied stress is to increase atomic mobility, thus enhancing the creep rate.
AFM surface image
Using AFM, surface offsets at shear bands were determined pre-and post-bending (bottom left).
Bending duration: 170 h (A) and 144 h (B).
The offset change is displayed as a function of initial offset prior to bending (top right).
The flow at shear bands is being further investigated.
In separate experiments, room-temperature anelastic deformation is used as a probe of defect sites, their creation and destruction by thermomechanical means.
Surface profile before and after constraint.