Microstructural evolution upon thermomechanical processing of non-sag tungsten

The thermally activated detachment of dislocations from bubbles may explain the variable stress sensitivity of the stationary creep in a broad stress region. The models of this kind of creep predict that, on the one hand, there should be an optimum bubble size that depends markedly on the applied stress while, on the other hand, the length of the bubble rows should play a secondary role, as the creep rate is primarily governed by the size of the individual bubbles. Although the kinetics of the detachment of the grain boundaries from bubbles should govern the final microstructure of non-sag tungsten both in the stress relieved and in the recrystallized conditions, a recent model on the thermally activated detachment will be really effective, only if the size of the dispersoid is in the nanosized region. A simple method is also described for monitoring the relaxation of the long-range residual stresses in thin non-sag wires.