Dislocation Mobility in High Purity LiF from 100°K to 300°K

Abstract

Understanding of the dynamic plastic response of polycrystalline materials requires understanding of the stress and temperature dependence of dislocation mobility in single crystals. At low driving stresses dislocation mobility can be described by a thermal activation model, based on a mechanism of jerky glide of dislocations between obstacles. The average dislocation velocity increases with both stress and temperature. On the other hand, at sufficiently high stresses, such as those generated in plate impact experiments on high purity single crystals, the primary resistance to the motion of dislocations is that of the clear lattice. Under these conditions the dislocation mobility is usually regarded as described by a viscous-drag model of the form

$$ {}_\tau b = B{\bar v_d} $$

(1)

where τ is the resolved shear stress, b is the Burgers’ vector, B is the so-called drag coefficient and ${\bar v_d}$ is the average dislocation velocity. According to currently accepted models for dislocation-phonon interaction, the drag coefficient B is expected to be proportional to the absolute temperature at temperatures from, say, 0.1 _D to 1.0 _D is the Deye temperature of the crystal.

Based on results presented in a thesis submitted by the first author in partial fulfillment of the requirements for a Ph.D. degree at Brown University.