Curved nanotwinned structure in Ni induced by dynamic compression

Abstract

Nanotwinned metals exhibit many interesting deformation behavior when compared to nanocrystalline materials with similar characteristic length scale. In this study, the deformation behavior of a nanotwinned Ni produced with a Ni-carbonyl chemical vapor deposition process was investigated via split Hopkinson pressure bar compression testing for strain rates ranging from 200 to 4100 s−1. This report will focus on the observation and analysis of an interesting microstructure formed as a result of the dynamic deformation; the collective curvature of the twin boundaries that makes up the nanotwinned structure. Furthermore, the curved twin boundaries tend to remain parallel to each other despite the introduction of curve. It is proposed that the formation of such a microstructure via dynamic deformation is likely a result of dislocation interactions with the twin boundaries forming steps made up of incoherent twin boundaries. A curvature can be formed with a large number of these steps formed on any single twin boundaries. The activation of this unique mechanism is dependent on the high strain rates, whereas the extent of operation is dependent on the extent of plastic deformation.