Direct Measurement of Mobility of Edge and Screw Dislocations in 3% Silicon-Iron by High Voltage Transmission Electron Microscopy

A new method to investigate directly the dynamical properties of dislocations was developed by means of HVEM. The motions of edge and screw dislocations were observed in thick foil specimens of Fe-Si being stretched in a HVEM operated at 500 kV. The dislocation motions were recorded continuously on a video tape recorder (VTR) with the aid of an image intensifier and the corresponding stress-strain curve was also recorded simultaneously. Edge dislocations moved well below the yield stress and the frequency of their motions increased with increasing applied stress. Lüders band nucleated at upper yield point and propagated in transition from upper to lower yield points. The motions of screws were observed immediately after upper yield point, accompanying dislocation multiplication. Edge dislocations had much higher mobility than screws but both of them moved much faster in comparison with the observation by etch-pitting technique.