Differentiation of Deformation Modes in Nanocrystalline Pd Films Inferred from Peak Asymmetry Evolution UsingIn SituX-Ray Diffraction

Abstract

Synchrotron-based in situ tensile testing was used to study the dominant deformation mechanisms of nanocrystalline Pd thin films on a compliant substrate. An x-ray diffraction peak profile analysis reveals an (hkl) independent deformation induced peak asymmetry. It is argued that the asymmetry is caused by a broad distribution of elastic strains among individual grains and the complexity of accommodation processes. The reversal of peak asymmetry manifests the transition from heterogeneous microplasticity to dislocation-based macroplasticity. Independently, stress-driven grain boundary migration is active.

Deformation-induced grain growth and twinning in nanocrystalline palladium thin films

“…This indicates that the applied stress was accommodated by grain boundary motion in addition to the observed twinning/detwinning. The observed grain growth is in line with a recent in-situ XRD study on the deformation behavior of similar sputter-deposited ncPd thin films [28], but is in contrast to measurements performed on electron beam evaporated Pd samples where no grain growth was reported up to 4% strain [29]. However, the same authors also compared the microstructure of electron-beam evaporated and magnetron sputtered samples [30] and found significantly higher initial twin densities in electron-beam evaporated Pd films.…”

“…On the experimental side, Lohmiller et al showed for comparable samples that the dislocation density begins to increase in the micro plastic regime starting from 0.3–0.4% applied strain [28,45]. A dislocation density of ρ = 3.5 · 10 −3 nm −2 was reported at 0% strain and 6 · 10 −3 nm −2 at 4% strain.…”

“…The difference suggests that grain boundary mediated deformation mechanisms have to be active to compensate for the remaining strain that does not come from dislocation/twin activity. Lohmiller et al has already reported other mechanisms, such as GB shear and slip, as well as GB migration resulting in grain growth [28,45]. …”

“…Additionally, similar samples were used for in-situ SXRD deformation experiments at the Material Science Beamline of the Swiss Light Source [28,45]. These samples were also subjected to tensile deformation at room temperature at a similar strain rate.…”

Mechanical stress and stress release channels in 10–350 nm palladium hydrogen thin films with different micro-structures

“…In Ref. [50] Lohmiller et al showed sliding to occur at lower strains than dislocation glide in tensile strained nanocrystalline Pd films, while it has not been observed in strained nanocrystalline Pd films with columnar structure in Refs. [6,31].…”