In situ Transmission Electron Microscopy Investigation of Electroplasticity in Single Crystal Nickel

Abstract

In situ Transmission Electron Microscopy (in situ TEM) tensile tests of single crystal nickel were performed in order to correlate direct observations of nanostructural changes resulting from applied mechanical and electrical stimuli in an effort to provide clarity on the mechanisms of electroplasticity (EP). A dual-tensile geometry was tested with an electrical push-to-pull device (EPTP) and digital image correlation (DIC) was used to track the location of dislocation nucleation along the sample surface. By analyzing the change in sample geometry precisely we are able to directly track individual dislocation motion as a result of the combined electromechanical actuation. From our observations, the pulsed electrical current leads to a more uniform deformation as compared to purely mechanically triggered plasticity. When the sample is undergoing stable plastic deformation, the pulsed current delays the formation of a stress concentration and distributes the deformation more uniformly. Our analysis finds that enhancement of surface nucleation from the electron wind force is more likely than Joule heating to be the origin of the more uniform plasticity observed during electrical pulsing.

Keywords: in situ TEM, nanomechanical test, electroplasticity, primary dislocation, slip band, surface dislocation nucleation