Abstract
The atomistic mechanisms active during plastic deformation of nanocrystalline metals are still a subject of controversy. The recently developed approach of combining automated crystal orientation mapping (ACOM) and in situ straining inside a transmission electron microscope was applied to study the deformation of nanocrystalline PdxAu1−x thin films. This combination enables direct imaging of simultaneously occurring plastic deformation processes in one experiment, such as grain boundary motion, twin activity and grain rotation. Large-angle grain rotations with ≈39° and ≈60° occur and can be related to twin formation, twin migration and twin–twin interaction as a result of partial dislocation activity. Furthermore, plastic deformation in nanocrystalline thin films was found to be partially reversible upon rupture of the film. In conclusion, conventional deformation mechanisms are still active in nanocrystalline metals but with different weighting as compared with conventional materials with coarser grains.
Highlights
Nanocrystalline (NC) metals and alloys with grain size below 100 nm exhibit outstanding mechanical properties, in particular, superior hardness, strength and fatigue properties as compared to their coarse grained counterparts [1,2,3,4,5]
All presented automated crystal orientation mapping (ACOM)-scanning TEM (STEM) orientation maps are superimposed with the reliability values in black, which constitute a measure for the unambiguousness of the orientation determination during the orientation assignment to the diffraction pattern
Previous in situ X-ray diffraction studies revealed reversible diffraction peak broadening in a loading–unloading cycle in NC Ni, which indicates the suppression of a build-up of a residual dislocation network during deformation in the nanograins [30]
Summary
Nanocrystalline (NC) metals and alloys with grain size below 100 nm exhibit outstanding mechanical properties, in particular, superior hardness, strength and fatigue properties as compared to their coarse grained counterparts [1,2,3,4,5]. This combination enables direct imaging of simultaneously occurring plastic deformation processes in one experiment, such as grain boundary motion, twin activity and grain rotation.
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