Geometry and kinetics of glide of screw dislocations in tungsten between 95K and 573K

In situ straining experiments were carried out in pure tungsten in order to study the geometry and kinetics of glide of dislocations as a function of stress and temperature. For tensile axes different from <110>, screw dislocations move by a combination of steady and jerky motion in planes which cannot be identified unambiguously. For a tensile axis close to <110>, however, screw dislocations have a much jerkier motion with jumps over large distances, in (112) planes exactly but only in the twinning direction, and in {123} planes. This involves a strong violation of the Schmid law, in agreement with slip line observations reported in the 60's by different authors. Jerky {112} slip is combined with a more classical steady motion in planes close to {110}, but the proportion of steady motion decreases rapidly to zero at decreasing temperature, which leads to a gradual transition between the two mechanisms. These results account for the specific mechanical properties measured in case of a <110> straining axis. They also bring new elements to understand the discrepancy between theoretical and experimental stress values at low temperatures. Indeed, like in Fe, local stress values as a function of temperature and dislocation velocity do not obey to the classical rules of thermodynamics, in agreement with possible quantum effects. (C) 2018 Published by Elsevier Ltd on behalf of Acta Materialia Inc.