Dislocation mobility in potassium and iron single crystals

Abstract

Dislocation velocities in potassium and iron single crystals were measured by the stress pulse method as a function of the resolved shear stress in the temperature region between room temperature and liquid helium temperature. The observed velocities ranged in value from about 10 m/s to 10 3 m/s, both in potassium and in iron. A linear relationship between the velocity and stress was observed at low stress levels. In potassium the velocity varied with the stress at a rate less than the linear at high stress and the extrapolated curves seem to approach the shear sound velocity. (Iron crystals were not tested at high enough stresses to observe a non-linear velocity - stress relationship). From the slope of the linear portion of the velocity- versus-stress curve a dislocation damping constant B was calculated. The value of B in potassium decreases with decreasing temperature from room temperature to 20°K. Below 20°K the value of B increases with decreasing temperature down to 4.2°K. In iron the value of B increases with decreasing temperature from room temperature to 4.2°K.