Dislocation Velocity in Single and Polycrystalline Silicon Iron

The stress dependence of screw dislocation velocity single and polycrystalline specimens of an iron-3.14% silicon alloy was measured by observation of slip band growth. An electrolytic etching technique was used to reveal dislocation intersections with the specimen surface, and slip bands were observed to form from fresh scratches and from grain boundaries as a result of pulse loading. Screw dislocation velocity on the {110} 〈111〉system in single crystals at room temperature followed the relation ν = (τ/τ_0)^n where n = 30.1. A plot of screw dislocation velocity vs. nominal resolved shear stress in individual grains of polycrystalline specimens shows considerable scatter which is attributed to the effects of stress variations due to elastic anisotropy. Observation of slip band growth in scratched and unscratched grains indicates that the stress required to activate grain boundary sources is greater than the stress required to propagate fresh dislocations.