The velocity of dislocations in pure iron monocrystals as a function of applied stress was measured by observing the change in length of dislocation slip bands after the application of a constant stress amplitude load pulse. Measurements covered a range of stresses from 10 to 500 Mdynes/cm2 and temperatures of 393, 295, 198, and 77°K.
The dislocation velocity at constant stress was found to be a sensitive function of temperature. However, the nature of the variation of the velocity with temperature was found to be inconsistent with theoretical formulations of thermally assisted dislocation motion. The nature of the disagreement between the experimental results and the thermal activation models is similar to that previously observed in niobium and Fe-3%Si . The decrease in dislocation velocity with decreasing temperature was also found to be too large to be attributed to hardening from the small amounts of impurities in the crystals.
The behavior of the dislocations as determined by this study was found to be consistent with predictions made from measurements of the macroscopic yield stress. However, the results of this study differ markedly from the behavior predicted from measurements of the strain rate sensitivity of the flow stress.
