Control of dynamic recovery and strength by subgrain boundaries – insights from stress-change tests on CaF2single crystals
The deformation behavior of single crystals of CaF2 was investigated at homologous temperatures of 0.45 ± 0.05. Stress (σ) changes comprising reductions by a factor up to about 2 were done to separate the dislocation processes. In agreement with previous results for pure Al and LiF, it was found that the response to σ-reductions in the steady state of deformation starts with a period of declining deformation rate before the normal transient reaction with work softening sets in. This first period shrinks significantly when the σ-reduction tests are performed at lower strains, i.e. earlier in the primary transient. Correlation with results for the microstructural evolution during the primary transient allows one to conclude that the transient response with declining after σ-reductions is due to subgrain-boundary migration under concentrated stress. The results indicate that dislocation walls in the form of cell and subgrain boundaries control the accumulation of dislocations in strain hardening and that the...