Deformation mechanisms in metallic glasses are notably different from conventional metals due to the absence of long range order and defects such as dislocations and grain boundaries. In situ high energy, X-ray and neutron diffraction techniques have been primarily used to study these deformation mechanisms. However, these techniques can be applied only to bulk, macroscopic samples. Therefore, the deformation behavior of metallic glasses at the micro and nanoscale has remained relatively unexplored.
We have used a novel technique (developed by our collaborators at University of Vienna) based on selected area electron diffraction (SAD) to measure the 2D elastic strain tensor from sub-micrometer regions of nanoscale metallic glass films. In this technique, the atomic-level elastic strain is derived by analyzing the deformation induced anisotropic geometric changes in the first diffuse ring of the SAD patterns. By concurrently measuring the macroscopic stress and strain, we have revealed the presence of significant anelastic deformation in the films. In addition, we have also shown that the deformation causes permanent atomic-scale structural rearrangements, even in the absence of macroscopic plasticity.
Top: Change in the reciprocal lattice vector (q) with the azimuthal angle χ in the SAD pattern due to applied strain. The change in q can be used to calculate the strain along different directions.
Bottom: Changes in normalized full-width-at-half-maximum (FWHM), which is related to the spread of nearest neighbor distances, as a function of applied stress.
Related Publications
1. R. Sarkar, C. Ebner, I. Izadi, C. Rentenberger, and J. Rajagopalan, “Revealing anelasticity and structural rearrangements in nanoscale metallic glass films using in situ TEM diffraction,” Materials Research Letters, 5, 135-143, 2017 (pdf).
2. C. Ebner, R. Sarkar, J. Rajagopalan, and C. Rentenberger, “Local, atomic-level elastic strain measurements of metallic glass thin films by electron diffraction,” Ultramicroscopy 165, 51–58, 2016 (pdf).