Mobility of Edge Dislocations in Silicon-Iron Crystals

Abstract

A method has been developed whereby the velocity of motion of fresh dislocations introduced into a crystal by scratching the surface may be measured as a function of stress. The velocities of unpinned edge dislocations in 3¼% silicon‐iron have been measured as a function of stress over a range of five orders of magnitude in velocity from 10⁻⁷ cm/sec to 10⁻² cm/sec. The velocity has been found to be very sensitive to the applied stress in this velocity range. Measurements of velocity as a function of stress have been made for four temperatures in the range 78°K to 373°K. It has been found that over this range of temperature the yield stress changes with temperature in the same way as the stress to produce a constant velocity of dislocation motion. From the result it is concluded that the rise in yield stress at low temperatures exhibited by this silicon iron is due primarily to an increase in the lattice resistance to dislocation motion and not to an increase in the Cottrell locking force. Preliminary experiments on pinned dislocations suggest that there may also be an effect of temperature on the strength of pinning by impurities which would be superimposed on the increase in lattice resistance with decreasing temperature.